Dr.  Lilienthal, 

230  W.  25th  St.,  New  York. 


THE  PROPERTY  OF 

ieal  Collep  sf  tie  Pacific. 


MEDICAL 


Cfe 


OF 


PHYSIOLOGY, 


BY 


WILLIAM  SENHOUSE  KIRKES,  M.D. 


EDITED    BY 


W.  MORRANT  BAKER,  F.R.C.S., 

LECTURER  ON  PHYSIOLOGY,  AND 

ASSISTANT  SURGEON  TO  ST.  BARTHOLOMEW'S  HOSPITAL  ;  SURGEON  TO 
THE  EVELINA  HOSPITAL  FOR  SICK  CHILDREN. 


WITH  TWO  HUNDRED  AND  FORTY-EIGHT  ILLUSTRATIONS. 


A  NEW  AMERICAN  FROM  THE  EIGHTH  ENLARGED 
ENGLISH  EDITION. 


HENRY     C.     L  E  A. 

1873. 


SHERMAN   &   CO.,   PRINTKES, 


PREFACE  TO  THE  EIGHTH  EDITION.' 


THE  Eighth  Edition  is  the  result  of  an  increased 
demand  for  this  work,  involving  the  necessity  for  a  re- 
print at  an  earlier  period  after  the  publication  of  the 
Seventh  Edition  than  was  anticipated.  The  opportunity 
has  been  seized  for  making  corrections  and  additions  where 
they  appeared  to  be  most  needed ;  but  the  present  issue 
must  be  regarded  as,  in  great  part,  a  reprint  of  the  Edition 
of  1869. 

W.  MORRANT  BAKER. 

THE  COLLEGE, 

ST.  BARTHOLOMEW'S  HOSPITAL, 
October,  1872. 


13547 


CONTENTS. 


CHAPTER  I. 

PAGE 

THE   GENERAL   AND   DISTINCTIVE  CHARACTERS   OF    LIVING 

BEINGS, 13 


CHAPTER  II. 

CHEMICAL  COMPOSITION  OF  THE  HUMAN  BODY,     ...  18 

CHAPTER  III. 

STRUCTURAL  COMPOSITION  OF  THE  HUMAN  BODY,.        .        .  26 

CHAPTER  IV. 

STRUCTURE  OF  THE  ELEMENTARY  TISSUES,     ....  34 

Epithelium, 34 

Areolar,  Cellular,  or  Connective  Tissue,      ....  38 

Adipose  Tissue, 40 

Pigment,       ..........  42 

Cartilage,               43 

Bones  and  Teeth, .46 

CHAPTER  V. 

THE  BLOOD, .55 

Quantity  of  Blood, 56 

Coagulation  of  the  Blood,    .......  58 

Conditions  affecting  Coagulation, 62 

1* 


VI  CONTENTS. 

PAGE 

Chemical  Composition  of  the  Blood,  .....  64 

The  Blood-Corpuscles,  or  Blood-cells,  .....  65 

Chemical  Composition  of  Ked  Blood-cells,  ....  68 

Blood-crystals, 69 

The  White  Corpuscles, 71 

The  Serum, 72 

Variations  in  the  Principal  Constituents  of  the  Liquor  San- 

guinis,    ..........  73 

Variations  in  Healthy  Blood  under  Different  Circumstances,  76 
Variations  in  the  Composition  of  the  Blood  in  Different 

Parts  of  the  Body, 77 

Gases  contained  in  the  Blood,  ......  81 

Development  of  the  Blood, 81 

Uses  of  the  Blood,  .  85 

Uses  of  the  various  Constituents  of  the  Blood,  .  .  .85 


CHAPTEK  VI. 

CIRCULATION  OF  THE  BLOOD, 88 

The  Systemic,  Pulmonary,  and  Portal  Circulations,   .         .       89 

THE  HEART, 91 

Structure  of  the  Valves  of  the  Heart, 92 

The  Action  of  the  Heart, 96 

Function  of  the  Valves  of  the  Heart, 99 

Sounds  of  the  Heart, 105 

Impulse  of  the  Heart,  ........     107 

Frequency  and  Force  of  the  Heart's  Action,  .  .  .  108 
Cause  of  the  Rhythmic  Action  of  the  Heart,  .  .  .111 
Effects  of  the  Heart's  Action,  .  .  .  .  .  .114 

THE  ARTERIES, 115 

Structure  of  the  Arteries, 115 

The  Pulse, •  .  .      .         .         .123 

Sphygmograph, 124 

Force  of  the  Blood  in  the  Arteries, 129 

Velocity  of  the  Blood  in  the  Arteries,          .         .         .         .131 

THE  CAPILLARIES, 131 

The  Structure  and  Arrangement  of  Capillaries,  .  .  .  132 
Circulation  in  the  Capillaries, 135 


CONTENTS.  Vll 

PAGE 

THE  VEINS, 141 

Structure, 141 

Agents  concerned  in  the  Circulation  of  the  Blood,       .         .  145 

Velocity  of  Blood  in  the  Veins, 147 

Velocity  of  the  Circulation, 147 

PECULIARITIES  OF  THE  CIRCULATION  IN  DIFFERENT  PARTS,  150 

Cerebral  Circulation, 150 

Erectile  Structures, 152 


CHAPTEE  VII. 

RESPIRATION, «         ,  155 

Position  and  Structure  of  the  Lungs,  ;  155 

Mechanism  of  Eespiration,   .......  161 

Respiratory  Movements,       ...;...  162 

Kespiratory  Khythm, 165 

Kespiratory  Movements  of  Glottis, 166 

Quantity  of  Air  respired,      .......  166 

Movements  of  the  Blood  in  Respiratory  Orgaiis, .         .         .  172 

Changes  of  the  Air  in  Respiration,        .....  173 

Changes  produced  in  the  Blood  by  Respiration,  .         .         .  179 

Mechanism  of  various  Respiratory  Actions,          .         .         .  180 

Influence  of  the  Nervous  System  in  Respiration,  .         .         .  185 

Effects  of  the  Suspension  and  Arrest  of  Respiration,    .         .  186 


CHAPTER  VIII. 

ANIMAL  HEAT,   .   .     .         .         .         .         .         .         .         .         .  189 

Variations  in  Temperature,  .......  190 

Sources  and  Mode  of  Production  of  Heat  in  the  Body,         .  192 

Regulation  of  Temperature,  .......  194 

Influence  of  Nervous  System,       ......  198 


CHAPTER  IX. 

DIGESTION, 199 

Food, 199 

Starvation, .         .  203 


Vlll  CONTENTS. 

PAGE 

PASSAGE  OF  FOOD  THROUGH  THE  ALIMENTARY  CANAL,    .        .  207 

The  Salivary  Glands  and  the  Saliva,     .....  209 

Passage  of  Food  into  the  Stomach, 213 

DIGESTION  OF  FOOD  IN  THE  STOMACH, 214 

Structure  of  the  Stomach, 214 

Secretion  and  Properties  of  the  Gastric  Fluid,      .         .         .  219 

Changes  of  the  Food  in  the  Stomach, 225 

Movements  of  the  Stomach, .......  231 

Influence  of  the  Nervous  System  on  Gastric  Digestion,       .  234 

Digestion  of  the  Stomach  after  Death,          ....  236 

DIGESTION  IN  THE  INTESTINES,  .......  238 

Structure  and  Secretion  of  the  Small  Intestines,  .         .         .  238 

Valvulse  Conniventes,  .         .         .         .         .         .         .         .  240 

Glands  of  the  Small  Intestine, 240 

The  Villi, 246 

Structure  of  the  Large  Intestine, ......  248 

The  Pancreas  and  its  Secretion,    ......  250 

Structure  of  the  Liver,         .......  252 

Functions  of  the  Liver,         .......  259 

The  Bile, 259 

Glycogenic  Function  of  the  Liver,        .....  267 
Summary  of  the   Changes  which  take   place  in  the  Food 

during  its  Passage  through  the  small  Intestine,    .         .  270 

Summary  of  the  Process  of  Digestion  in  the  large  Intestine,  272 

Gases  contained  in  the  Stomach  and  Intestines,  .         .         .  274 

Movements  of  the  Intestines,         ......  275 

CHAPTER  X. 

ABSORPTION,        ..........  277 

Structure  and  Office  of  the  Lacteal  and  Lymphatic  Vessels, 

and  Glands, 277 

Lymphatic  Glands, .283 

Properties  of  Lyrnph  and  Chyle,         .....  286 

Absorption  by  the  Lacteal  Vessels,      .....  290 

Absorption  by  the  Lymphatics,  ......  291 

Absorption  by  Bloodvessels,          ......  293 

CHAPTER  XL 

NUTRITION  AND  GROWTH,         .......  299 

Nutrition, 299 

Growth, .  311 


CONTENTS.  IX 
CHAPTER  XII. 

PAGE 

SECRETION, 313 

Secreting  Membranes,  ........  314 

Serous  Membranes, 315 

Mucous  Membranes, 316 

Secreting  Glands,          ........  319 

Process  of  Secretion, 321 

•» 

CHAPTER  XIII. 

VASCULAR  GLANDS,  OR  GLANDS  WITHOUT  DUCTS,    .        .        .  325 

Structure  of  the  Spleen, 327 

Functions  of  the  Vascular  Glands,       .....  329 

CHAPTER  XIV. 

THE  SKIN  AND  ITS  SECRETIONS, 332 

Structure  of  the  Skin, 333 

Structure  of  Hair  and  Nails,         ......  340 

Excretion  by  the  Skin, 344 

Absorption  by  the  Skin,       .......  347 

CHAPTER  XV.  ^ 

THE  KIDNEYS  AND  THEIR  SECRETION, 349 

Structure  of  the  Kidneys,     .......  349 

Secretion  of  Urine,        ........  354 

The  Urine ;  its  General  Properties,     .         .         .         .         .  356 

Chemical  Composition  of  the  Urine,    .         .         .         .     -  .  357 

CHAPTER  XVI. 

THE  NERVOUS  SYSTEM,      ........  367 

Elementary  Structures  of  the  Nervous  System,  .         .         .  368 

Functions  of  Nerve-fibres,    .         .         .         .         .         .         .  376 

Functions  of  Nerve-centres,          ......  382 

CEREBRO-SPINAL  NERVOUS   SYSTEM,        .....  386 

Spinal  Cord  and  its  Nerves, 386 

Functions  of  the  Spinal  Cord, 392 


X  CONTENTS. 

PAGE 

THE  MEDULLA  OBLONGATA, 402 

Its  Structure, 402 

Distribution  of  the  Fibres  of  the  Medulla  Oblongata,         .  404 

Functions  of  the  Medulla  Oblongata, 405 

STRUCTURE  AND  PHYSIOLOGY  OF  THE  PONS  VAROLII,  CRURA 
CEREBRI,  CORPORA  QUADRIGEMINA,  CORPORA  GENIC- 

ULATA,  OPTIC  THALAMI,  AND  CORPORA  STRIATA,  .        .  409 

PonsVarolii, 409 

Crura  Cerebri, 409 

Corpora  Quadrigemina,         .......  411 

The  Sensory  Ganglia, 413 

STRUCTURE  AND  PHYSIOLOGY  OF  THE  CEREBELLUM,        .        .  414 
STRUCTURE  AND  PHYSIOLOGY  OF  THE  CEREBRUM,     .        .        .419 

PHYSIOLOGY  OF  THE  CEREBRAL  AND  SPINAL  NERVES,      .        .  424 
Physiology  of  the  Third,  Fourth,  and  Sixth  Cerebral  or 

Cranial  Nerves, 425 

Physiology  of  the  Fifth  or  Trigeminal  Nerve,     .         .         .  428 

Physiology  of  the  Facial  Nerve, 433 

Physiology  of  the  Glosso-pharyngeal  Nerve,       .         .         .  435 

Physiology  of  the  Pneumogastric  Nerve,     ....  438 

Physiology  of  the  Spinal  Accessory  Nerve,          .         .         .  443 

Physiology  of  the  IJypoglossal  Nerve,          ....  444 

Physiology  of  the  Spinal  Nerves, 444 

PHYSIOLOGY  OF  THE  SYMPATHETIC  NERVE,    ....  445 


CHAPTER  XVII. 

CAUSES  AND  PHENOMENA  OF  MOTION,     .....  454 

Ciliary  Motion,     .........  454 

Muscular  Motion,          ........  456 

Muscular  Tissue, 456 

Properties  of  Muscular  Tissue,     ......  461 

Action  of  the  Voluntary  Muscles, 467 

Action  of  the  Involuntary  Muscles,     .....  473 

Source  of  Muscular  Action,  473 


CONTENTS.  XI 


CHAPTER  XVIII. 

PAGE 

Or  VOICE  AND  SPEECH, 474 

Mode  of  Production  of  the  Human  Voice,  ....  474 

The  Larynx, 476 

Application  of  the  Voice  in  Singing  and  Speaking,     .         .  483 

SPEECH,  486 


CHAPTER  XIX. 

THE  SENSES, 489 

THE  SENSE  OF  SMELL, 494 

THE  SENSE  OF  SIGHT, 499 

Structure  of  the  Eye, 499 

Phenomena  of  Vision, 507 

Reciprocal  Action  of  different  parts  of  the  Retina,  .         .  519 

Simultaneous  Action  of  the  two  Eyes,     .         .         .      '  .  521 

THE  SENSE  OF  HEARING,        .......  527 

Anatomy  of  the  Organ  of  Hearing,      .....  527 

Physiology  of  Hearing,         .......  534 

Functions  of  the  External  Ear. 535 

Functions  of  the  Middle  Ear;  the  Tympanum,  Ossicula,  and 

Fenestrae, •  536 

Functions  of  the  Internal  Ear 541 

Sensibility  of  the  Auditory  Nerve,       .....  543 

THE  SENSE  OF  TASTE, 547 

THE  SENSE  OF  TOUCH, 554 


CHAPTER  XX. 

GENERATION  AND  DEVELOPMENT,     ......  559 

Generative  Organs  of  the  Female, 560 

Unimpregnated  Ovum,         .......  563 

Discharge  of  the  Ovum,        .......  567 

Corpus  Luteum, 570 


Xll  CONTENTS. 

PAGE 

IMPREGNATION  OF  THE  OVUM, 573 

Male  Sexual  Functions, 573 

DEVELOPMENT, 578 

Changes  of  the  Ovum  previous  to  the  Formation  of  the 

Embryo, 578 

Changes  of  the  Ovum  within  the  Uterus,     ....  581 

The  Umbilical  Vesicle, 582 

The  Amnion  and  Allantois, ........  585 

The  Chorion, 588 

Changes  of  the  Mucous  Membrane  of  the  Uterus  and  For- 
mation of  the  Placenta, 589 

DEVELOPMENT  OF  ORGANS, 593 

Development  of  the  Vertebral  Column  and  Cranium,         .  594 

Development  of  the  Face  and  Visceral  Arches,  .         .         .  595 

Development  of  the  Extremities,          .....  596 

Development  of  the  Vascular  System,          ....  597 
Circulation  of  Blood  in  the  Foetus,       .         .         .         .         .601 

Development  of  the  Nervous  System, .....  603 

Development  of  the  Organs  of  Sense, 603 

Development  of  the  Alimentary  Canal,       ....  606 
Development  of  the  Respiratory  Apparatus,        .         .         .  608 
The  Wolffian  Bodies,  Urinary  Apparatus,  and  Sexual  Or- 
gans,         609 

THE  MAMMARY  GLANDS, 613 

LIST  OF  WORKS  REFERRED  TO, 617 

INDEX,        .  625 


HANDBOOK  OF  PHYSIOLOGY. 


CHAPTER  I. 

ON   THE   GENERAL   AND   DISTINCTIVE   CHARACTERS    OF 
LIVING    BEINGS. 

HUMAN  PHYSIOLOGY  is  the  science  which  treats  of  the  life 
of  man — of  the  way  in  which  he  lives,  and  moves,  and  has  his 
being.  It  teaches  how  man  is  begotten  and  born ;  how  he 
attains  maturity ;  and  how  he  dies. 

Having,  then,  man  as  the  object  of  its  study,  it  is  unneces- 
sary to  speak  here  of  the  laws  of  life  in  general,  and  the  means 
by  which  they  are  carried  out,  further  than  is  requisite  for  the 
more  clear  understanding  of  those  of  the  life  of  man  in  par- 
ticular. Yet  it  would  be  impossible  to  understand  rightly  the 
working  of  a  complex  machine  without  some  knowledge  of  its 
motive  power  in  the  simplest  form ;  and  it  may  be  well  to  see 
first  what  are  the  so-called  essentials  of  life — those,  namely, 
which  are  manifested  by  all  living  beings  alike,  by  the  lowest 
vegetable  and  the  highest  animal,  before  proceeding  to  the  con- 
sideration of  the  structure  and  endowments  of  the  organs  and 
tissues  belonging  to  man. 

The  essentials  of  life  are  these, — birth,  growth  and  develop- 
ment, decline  and  death ;  and  an  idea  of  what  life  is,  will  be 
best  gained  by  sketching  these  events,  each  in  succession,  and 
their  relations  one  to  another. 

The  term,  birth,  when  employed  in  this  general  sense  of  one 
of  the  conditions  essential  to  life,  without  reference  to  any  par- 
ticular kind  of  living  being,  may  be  taken  to  mean,  separation 
from  a  parent,  with  a  greater  or  less  power  of  independent  ex- 
istence as  a  living  being. 

Taken  thus,  the  term,  although  not  defining  any  particular 
stage  in  development,  serves  well  enough  for  the  expression  of 
the  fact,  to  which  no  exception  has  yet  been  proved  to  exist, 
that  the  capacity  for  life  in  all  living  beings  is  got  by  in- 
heritance. 


14  GROWTH. 

Growth,  or  inherent  power  of  increasing  in  size,  although 
essential  to  our  idea  of  life,  is  not  a  property  of  living  beings 
only.  A  crystal  of  sugar  or  of  common  salt,  or  of  any  other 
substance,  if  placed  under  appropriate  conditions  for  obtaining 
fresh  material,  will  grow  in  a  fashion  as  definitely  character- 
istic and  as  easily  to  be  foretold  as  that  of  a  living  creature. 
It  is,  therefore,  necessary  to  explain  the  distinctions  which  exist 
in  this  respect  between  living  and  lifeless  structures ;  for  the 
manner  of  growth  in  the  two  cases  is  widely  different. 

First,  the  growth  of  a  crystal,  to  use  the  same  example  as 
before,  takes  place  merely  by  additions  to  its  outside ;  the  new 
matter  is  laid  on  particle  by  particle,  and  layer  by  layer,  and, 
when  once  laid  on,  it  remains  unchanged.  The  growth  is  here 
said  to  be  superficial.  In  a  living  structure,  on  the  other  hand, 
as,  for  example,  a  brain  or  a  muscle,  where  growth  occurs,  it 
is  by  addition  of  new  matter,  not  to  the  surface  only,  but 
throughout  every  part  of  the  mass ;  the  growth  is  not  super- 
ficial, but  interstitial.  In  the  second  place,  all  living  structures 
are  subject  to  constant  decay ;  and  life  consists,  not  as  once 
supposed,  in  the  power  of  preventing  this  never-ceasing  decay, 
but  rather  in  making  up  for  the  loss  attendant  on  it  by  never- 
ceasing  repair.  Thus,  a  man's  body  is  not  composed  of  ex- 
actly the  same  particles  day  after  day,  although  to  all  intents 
he  remains  the  same  individual.  Almost  every  part  is  changed 
by  degrees;  but  the  change  is  so  gradual,  and  the  renewal  of 
that  which  is  lost  so  exact,  that  no  difference  may  be  noticed, 
except  at  long  intervals  of  time.  A  lifeless  structure,  as  a 
crystal,  is  subject  to  no  such  laws ;  neither  decay  nor  repair  is 
a  necessary  condition  of  its  existence.  That  which  is  true  of 
structures  which  never  had  to  do  with  life  is  true  also  with  re- 
spect to  those  which,  though  they  are  formed  by  living  parts, 
are  not  themselves  alive.  Thus,  an  oyster-shell  is  formed  by 
the  living  animal  which  it  incloses,  but  it  is  a£  lifeless  as  any 
other  mass  of  saline  matter;  and  in  accordance  with  this  cir- 
cumstance its  growth  takes  place  not  inter  stitially,  but  layer  by 
layer,  and  it  is  not  subject  to  the  constant  decay  and  recon- 
struction which  belong  to  the  living.  The  hair  and  nails  are 
examples  of  the  same  fact. 

Thirdly.  In  connection  with  the  growth  of  lifeless  masses 
there  is  no  alteration  in  composition  or  properties  of  the  ma- 
terial which  is  taken  up  and  added  to  the  previously  existing 
mass.  For  example,  when  a  crystal  of  common  salt  grows  on 
being  placed  in  a  fluid  which  contains  the  same  material,  the 
properties  of  the  salt  are  not  changed  by  being  taken  out  of  the 
liquid  by  the  crystal  and  added  to  its  surface  in  a  solid  form. 
But  the  case  is  essentially  different  from  this  in  living  beings, 


DEVELOPMENT.  15 

both  animal  and  vegetable.  A  plant,  like  a  crystal,  can  only 
grow  when  fresh  material  is  presented  to  it ;  and  this  is  ab- 
sorbed by  its  leaves  and  roots ;  and  animals  for  the  same  pur- 
pose of  getting  new  matter  for  growth  and  nutrition,  take  food 
into  their  stomachs.  But  in  both  these  cases  the  materials  are 
much  altered  before  they  are  finally  assimilated  by  the  struc- 
tures they  are  destined  to  nourish. 

Fourthly.  The  growth  of  all  living  things  has  a  definite 
limit,  and  the  law  which  governs  this  limitation  of  increase  in 
size  is  so  invariable  that  we  should  be  as  much  astonished  to 
find  an  individual  plant  or  animal  without  limit  as  to  growth 
as  without  limit  to  life. 

Development  is  as  constant  an  accompaniment  of  life  as 
growth.  The  term  is  used  to  indicate  that  change  to  which,  be- 
fore maturity,  all  living  parts  are  constantly  subject,  and  by 
which  they  are  made  more  and  more  capable  of  performing 
their  several  functions.  For  example,  a  full-grown  man  is  not 
simply  a  magnified  child  ;  his  tissues  and  organs  have  not  only 
grown,  or  increased  in  size,  they  have  also  developed,  or  become 
better  in  quality. 

No  very  accurate  limit  can  be  drawn  between  the  end  of  de- 
velopment and  the  beginning  of  decline  ;  and  the  two  processes 
may  be  often  seen  together  in  the  same  individual.  But  after 
a  time  all  parts  alike  share  in  the  tendency  to  degeneration, 
and  this  is  at  length  succeeded  by  death. 

The  decline  of  living  beings  is  as  definite  in  its  occurrence 
as  growth  or  development.  Death — not  by  disease  or  injury — 
so  far  from  being  a  violent  interruption  of  the  course  of  life,  is 
but  the  fulfilment  of  a  purpose  in  view  from  the  commence- 
ment. 

It  has  been  already  said  that  the  essential  features  of  life 
are  the  same  in  all  living  things ;  in  other  words,  in  the  mem- 
bers of  both  the  animal  and  vegetable  kingdoms.  It  may  be 
well  now  to  notice  briefly  the  distinctions  which  exist  between 
the  members  of  these  two  kingdoms.  It  may  seem,  indeed,  a 
strange  notion  that  it  is  possible  to  confound  vegetables  with 
animals,  but  it  is  true  with  respect  to  the  lowest  of  them  in 
which  but  little  is  manifested  beyond  the  essentials  of  life, 
which  are  the  same  in  both. 

I.  Perhaps  the  most  essential  distinction  is  the  presence  or 
absence  of  power  to  live  upon  inorganic  material;  in  other 
words,  to  act  chemically  on  carbonic  acid,  ammonia,  and  water, 
so  as  to  make  use  of  their  component  elements  as  food.  Indeed 
one  ought  probably  to  say  that  a  question  concerning  the  capa- 
bility of  the  lower  kinds  of  animal  to  live  in  this  way  cannot 
be  entertained;  and  that  such  a  manner  pf  life  should  decide 


16  ANIMALS   CONTRASTED 

at  once  in  favor  of  a  vegetable  nature,  whatever  might  be  the 
attributes  which  seem  to  point  to  an  opposite  conclusion.  The 
power  of  living  upon  organic  matter  would  seem  to  be  less  de- 
cisive of  an  animal  nature,  for  some  fungi  appear  to  derive  sup- 
port almost  entirely  from  this  source. 

II.  There  is,  commonly,  a  marked  difference  in   general 
chemical  composition  between  vegetables  and  animals,  even  in 
their  lowest  forms ;  for  while  the  former  consist  mainly  of  a 
substance  containing  carbon,  hydrogen,  and  oxygen  only,  ar- 
ranged so  as  to  form  a  compound  closely  allied  to  starch,  and 
called  cellulose,  the  latter  are  commonly  composed  in  great 
part  of  the  three  elements  just  named,  together  with  a  fourth, 
nitrogen;  the  proximate  principles  formed  from  these  being 
identical,  or  nearly  so,  with  albumen.    It  must  not  be  supposed, 
however,  that  either  of  these  typical  compounds  alone,  with 
its  allies,  is  confined  to  one  kingdom  of  nature.     Nitrogenous 
or  albuminous  compounds  are  freely  produced  by  vegetable 
structures,  although  they  form  an  infinitely  smaller  proportion 
of  the  whole  organism  than  cellulose  or  starch.     And  while 
the  presence  of  the  latter  in  animals  is  much  more  rare  than 
is  that  of  the  former  in  vegetables,  there  are  many  animals  in 
which  traces  of  it  may  be  discovered,  and  some,  the  Ascidians, 
in  which  it  is  found  in  considerable  quantity. 

III.  Inherent  power  of  movement  is  a  quality  which  we  so 
commonly  consider  an  essential  indication  of  animal  nature, 
that  it  is  difficult  at  first  to  conceive  it  existing  in  any  other. 
The  capability  of  simple  motion  is  now  known,  however,  to 
exist  in  so  many  vegetable  forms,  that  it  can  no  longer  be  held 
as  ail  essential  distinction   between  them  and  animals,  and 
ceases  to  be  a  mark  by  which  the  one  can  be  distinguished 
from  the  other.     Thus  the  zoospores  of  many  of  the  Crypto- 
gamia  exhibit  movements  of  a  like  kind  to  those  seen  in  animal- 
cules ;  and  even  among  the  higher  orders  of  plants,  many  ex- 
hibit such  motion,  either  at  regular  times,  or  on  the  application 
of  external  irritation,  as  might  lead  one,  were  this  fact  taken 
by  itself,  to  regard  them  as  sentient  beings.     Inherent  power 
of  movement,  then,  although  especially  characteristic  of  ani- 
mal nature,  is,  when  taken  by  itself,  no  proof  of  it.     Of  course, 
if  the  movement  were  such  as  to  indicate  any  kind  of  purpose, 
whether  of  getting  food  or  any  other,  the  case  would  be  differ- 
ent, and  we  should  justly  call  a  being  exhibiting  such  motion, 
an  animal.     But  low  down  in  the  scale  of  life,  where  alone 
there  exists  any  difficulty  in  distinguishing  the  two  classes, 
movements,  although  almost  always  more  lively,  are  scarcely 
or  not  at  all  more  purposive  in  one  than  the  other ;  and  even 
if  we  decide  on  the  animal  nature  of  a  being,  it  by  no  means 


WITH    VEGETABLES.  17 

follows  that  we  are  bound  to  acknowledge  the  presence  of  sen- 
sation or  volition  in  the  slightest  degree.  There  may  be  at 
least  no  evidence  of  its  possessing  a  trace  of  those  tissues,  ner- 
vous and  muscular,  by  which,  in  the  higher  members  of  the 
animal  kingdom,  these  qualities  are  manifested.  Probably 
there  is  no  more  of  either  of  them  in  the  lowest  animals  than 
in  vegetables.  In  both,  movement  is  eifected  by  the  same 
means — ciliary  action,  and  hence  the  greater  value,  for  pur- 
poses of  classification,  of  the  power  to  live  on  this  or  that  kind 
of  food — on  organic  or  inorganic  matter.  As  the  main  purpose 
of  the  lowest  members  of  the  vegetable  kingdom  is  doubtless  to 
bring  to  organic  shape  the  elements  of  the  inorganic  world 
around,  so  the  function  of  the  lowest  animals  is,  in  like  man- 
ner, to  act  on  degenerating  organic  matter — "to  arrest  the 
fugitive  organized  particles,  and  turn  them  back  into  the  as- 
cending stream  of  animal  life."  And,  because  sensation  and 
volition  are  accompaniments  of  life  in  somewhat  higher  animal 
forms,  it  is  needless  to  suppose  that  these  qualities  exist  under 
circumstances  in  which,  as  we  may  believe,  they  could  be  of 
no  service.  It  is  as  needless  as  to  dogmatize  on  the  opposite 
side,  and  say  that  no  feeling  or  voluntary  movement  is  possible 
without  the  presence  of  those  tissues  which  we  call  nervous  and 
muscular. 

IV.  The  presence  of  a  stomach  is  a  very  general  mark  by 
which  an  animal  can  be  distinguished  from  a  vegetable.  But 
the  lowest  animals  are  surrounded  by  material  that  they  can 
take  as  food,  as  a  plant  is  surrounded  by  an  atmosphere  that 
it  can  use  in  like  manner.  And  every  part  of  their  body 
being  adapted  to  absorb  and  digest,  they  have  no  need  of  a 
special  receptacle  for  nutrient  matter,  and  accordingly  have 
no  stomach.  This  distinction  then  is  not  a  cardinal  one. 

It  would  be  tedious  as  well  as  unnecessary  to  enumerate  the 
chief  distinctions  between  the  more  highly  developed  animals 
and  vegetables.  They  are  sufficiently  apparent.  It  is  neces- 
sary to  compare,  side  by  side,  the  lowest  members  of  the  two 
kingdoms,  in  order  to  understand  rightly  how  faint  are  the 
boundaries  between  them. 


18       CHEMICAL   COMPOSITION   OF    HUMAN    BODY. 


CHAPTER  II. 

CHEMICAL   COMPOSITION   OF   THE   HUMAN   BODY. 

THE  following  Elementary  Substances  may  be  obtained  by 
chemical  analysis  from  the  human  body :  Oxygen,  Hydrogen, 
Nitrogen,  Carbon,  Sulphur,  Phosphorus,  Silicon,  Chlorine, 
Fluorine,  Potassium,  Sodium,  Calcium,  Magnesium,  Iron,  and, 
probably  as  accidental  constituents,  Manganesium,  Alumin- 
ium, Copper,  and  Lead.  Thus,  of  the  sixty-three  or  more 
elements  of  which  all  known  matter  is  composed,  more  than 
one  fourth  are  present  in  the  human  body. 

Only  one  or  two  elements,  and  in  very  minute  amount,  are 
present  in  the  body  uncombined  with  others  ;  and  even  these 
are  present  much  more  abundantly  in  various  states  of  combi- 
nation. The  most  simple  compounds  formed  by  union  in 
various  proportions  of  these  elements  are  termed  proximate 
principles ;  while  the  latter  are  classified  as  the  organic  and  the 
inorganic  proximate  principles. 

The  term  organic  was  once  applied  exclusively  to  those 
substances  which  were  thought  to  be  beyond  the  compass  of 
synthetical  chemistry  and  to  be  formed  only  by  organized  or 
living  beings,  animal  or  vegetable ;  these  being  called  organ- 
ized, inasmuch  as  they  are  characterized  by  the  possession  of 
different  parts  called  organs.  But  with  advancing  knowledge, 
both  distinctions  have  disappeared ;  and  while  the  title  of 
Mving  organism  is  applied  to  numbers  of  living  things,  having 
no  trace  of  organs  in  the  old  sense  of  the  term,  and  in  some, 
so  far  as  can  be  now  seen,  in  no  other  sense,  the  term  organic 
has  long  ceased  to  be  applied  to  substances  formed  only  by 
living  tissues.  In  other  words,  substances,  once  thought  to  be 
formed  only  by  living  tissues,  are  still  termed  organic,  al- 
though they  can  be  now  made  in  the  laboratory.  The  term, 
indeed,  in  its  old  meaning,  becomes  year  by  year  applicable 
to  fewer  substances,  as  the  chemist  adds  to  his  conquests  over 
inorganic  elements  and  compounds,  and  moulds  them  to  more 
complex  forms. 

Although  a  large  number  of  so-called  organic  compounds 
have  long  ceased  to  be  peculiar  in  being  formed  only  by  living 
tissues,  the  terms  organic  and  inorganic  are  still  commonly 
used  to  denote  distinct  classes  of  chemical  substances,  and  the 
classification  of  the  matters  of  which  the  human  body  is  com- 


CHEMICAL   COMPOSITION   OF   HUMAN   BODY.       19 

posed  into  the  organic  and  the  inorganic  is  convenient,  and 
will  be  here  employed. 

No  very  accurate  line  of  separation  can  be  drawn  between 
organic  and  inorganic  substances,  but  there  are  certain  pecu- 
liarities belonging  to  the  former  which  may  be  here  briefly 
noted. 

1.  Organic  compounds  are  composed  of  a  larger  number  of 
Elements  than  are  present  in  the  more  common  kinds  of  inor- 
ganic matter.     Thus,  albumen,  fibrin,  and  gelatin,  the  most 
abundant  substances  of  this  class,  in  the  more  highly  organized 
tissues  of  animals,  are  composed  of  five  elements, — carbon,  hy- 
drogen, oxygen,  nitrogen,  and  sulphur.     The  most  abundant 
inorganic  substance,  water,  has  but  two  elements,  hydrogen 
and  oxygen. 

2.  Not  only  are  a  large  number  of  elements  usually  com- 
bined in  an  organic  compound,  but  a  large  number  of  equiva- 
lents or  atoms  of  each  of  the  elements  are  united  to  form  an 
equivalent  or  atom  of  the  compound.     In  the  case  of  carbon- 
ate of  ammonium,  as  an  example  among  inorganic  substances, 
one  equivalent  of  carbonic  acid  is  united  with  two  of  ammo- 
nium ;  the  equivalent  or  atom  of  carbonic  acid  consists  of  one 
of  carbon  with  two  of  oxygen ;  and  that  of  ammonium  of  one 
of  nitrogen  with  three  of  hydrogen.     But  in  an  equivalent  or 
atom  of  fibrin,  or  of  albumen,  there  are  of  the  same  elements, 
respectively,  72,  22,  18,  and  112  equivalents.     And,  together 
with  this  union  of  large  numbers  of  equivalents  in  the  organic 
compound,  it  is  further  observable,  that  the  several  numbers 
stand  in  no  simple  arithmetical  relation  one  with  another,  as 
the  numbers  of  equivalents  combining  in  an  inorganic  com- 
pound do. 

With  these  peculiarities  in  the  chemical  composition  of  or- 
ganic bodies  we  may  connect  two  other  consequent  facts ;  first, 
the  large  number  of  different  compounds  that  are  formed  out 
of  comparatively  few  elements ;  secondly,  their  great  proneuess 
to  decomposition.  For  it  is  a  general  rule,  that  the  greater 
the  number  of  equivalents  or  atoms  of  an  element  that  enter 
into  the  formation  of  an  atom  of  a  compound,  the  less  is  the 
stability  of  that  compound.  Thus,  for  example,  among  the 
various  oxides  of  lead  and  other  metals,  the  least  stable  in 
composition  are  those  in  which  each  equivalent  has  the  largest 
number  of  equivalents  of  oxygen.  So,  water,  composed  of  one 
equivalent  of  oxygen  and  two  of  hydrogen,  is  not  changed  by 
any  slight  force ;  but  peroxide  of  hydrogen,  which  has  two 
equivalents  of  oxygen  to  two  of  hydrogen,  is  among  the  sub- 
stances most  easily  decomposed. 

The  instability,  on  this  ground,  belonging  to  organic  com- 


20      CHEMICAL   COMPOSITION   OF   HUMAN   BODY. 

pounds,  is,  in  those  which  are  most  abundant  in  the  highly 
organized  tissues  of  animals,  augmented,  1st,  by  their  contain- 
ing nitrogen,  which,  among  all  the  elements,  may  be  called  the 
least  decided  in  its  affinities,  and  that  which  maintains  with 
least  tenacity  its  combinations  with  other  elements;  and  2dly, 
by  the  quantity  of  water  which,  in  their  natural  state,  is  com- 
bined with  them,  and  the  presence  of  which  furnishes  a  most 
favorable  condition  for  the  decomposition  of  nitrogenous  com- 
pounds. Such,  indeed,  is  the  instability  of  animal  compounds, 
arising  from  these  several  peculiarities  in  their  constitution, 
that,  in  dead  and  moist  animal  matter,  no  more  is  requisite 
for  the  occurrence  of  decomposition  than  the  presence  of  at- 
mospheric air  and  a  moderate  temperature  ;  conditions  so  com- 
monly present,  that  the  decomposition  of  dead  animal  bodies 
appears  to  be,  and  is  generally  called,  spontaneous.  The  modes 
of  such  decomposition  vary  according  to  the  nature  of  the  origi- 
nal compound,  the  temperature,  the  access  of  oxygen,  the  pres- 
ence of  microscopic  organisms,  and  other  circumstances,  and 
constitute  the  several  processes  of  decay  and  putrefaction ;  in 
the  results  of  which  processes  the  only  general  rule  seems  to 
be,  that  the  several  elements  of  the  original  compound  finally 
unite  to  form  those  substances,  whose  composition  is,  under 
the  circumstances,  most  stable. 

The  organic  compounds  existing  in  the  human  body  may 
be  arranged  in  two  classes,  namely,  the  azotized,  or  nitrogenous, 
and  the  non-azotized,  or  non-nitrogenous  principles. 

The  non-azotized  principles  include  the  several  fatty,  oily, 
or  oleaginous  substances,  as  olein,  stearin,  cholesterin,  and 
others.  In  the  same  category  of  non-nitrogenous  substances 
may  be  included  lactic  and  formic  acids,  animal  glucose,  sugar 
of  milk,  &c. 

The  oily  or  fatty  matter  which,  inclosed  in  minute  cells, 
forms  the  essential  part  of  the  adipose  or  fatty  tissue  of  the 
human  body  (p.  40),  and  which  is  mingled  in  minute  particles 
in  many  other  tissues  and  fluids,  consists  of  a  mixture  of  stearin, 
palmitin,  and  olein.  The  mixture  forms  a  clear  yellow  oil,  of 
which  different  specimens  congeal  at  from  45°  to  35°. 

Cholesterin,  a  fatty  matter  which  melts  at  293°  F.,  and  is, 
therefore,  always  solid  at  the  natural  temperature  of  the  body, 
may  be  obtained  in  small  quantity  from  blood,  bile,  and  ner- 
vous matter.  It  occurs  abundantly  in  many  biliary  calculi ; 
the  pure  white  crystalline  specimens  of  these  concretions  being 
formed  of  it  almost  exclusively.  Minute  rhomboidal  scale- 
like  crystals  of  it  are  also  often  found  in  morbid  secretions,  as 
in  cysts,  the  puriform  matter  of  softening  and  ulcerating 
tumors,  &c.  It  is  soluble  in  ether  and  boiling  alcohol ;  but 


GELATINOUS    SUBSTANCES.  21 

alkalies  do  Dot  change  it;  it  is  one  of  those  fatty  substances 
which  are  not  saponifiable. 

The  azotized  or  nitrogenous  principles  in  the  human  body 
include  what  may  be  called  the  proper  gelatinous  and  albu- 
minous substances,  besides  others  of  less  definite  rank  and 
composition,  as  pepsin  and  ptyalin,  horny  matter  or  keratin, 
many  coloring  and  extractive  matters,  &c. 

The  gelatinous  substances  are  contained  in  several  of  the 
tissues,  especially  those  which  serve  a  passive  mechanical 
office  in  the  economy ;  as  the  cellular,  or  fibro-cellular  tissue 
in  all  parts  of  the  body,  the  tendons,  ligaments,  and  other 
fibrous  tissues,  the  cartilages  and  bones,  the  skin  and  serous 
membranes.  These,  when  boiled  in  water,  yield  a  material, 
the  solution  of  which  remains  liquid  while  it  is  hot,  but  be- 
comes solid  and  jelly-like  on  cooling. 

Two  varieties  of  these  substances  are  described,  gelatin  and 
chondrin,  the  latter  being  derived  from  cartilages,  the  former 
from  all  the  other  tissues  enumerated  above,  and  in  its  purest 
state,  from  isinglass,  which  is  the  swimming-bladder  of  the 
sturgeon,  and  which,  with  the  exception  of  about  7  per  cent, 
of  its  weight,  is  wholly  reducible  into  gelatin.  The  most  char- 
acteristic property  of  gelatin  is  that  already  mentioned,  of  its 
solution  being  liquid  when  warm,  and  solidifying  or  setting 
when  it  cools.  The  temperature  at  which  it  becomes  solid,  the 
proportion  of  gelatin  which  must  be  in  solution,  and  the  firm- 
ness of  the  jelly  when  formed,  are  various,  according  to  the 
source,  the  quantity,  and  the  quality  of  the  gelatin;  but,  as  a 
general  rule,  one  part  of  dry  gelatin  dissolved  in  100  of  water, 
will  become  solid  when  cooled  to  60°.  The  solidified  jelly 
may  be  again  made  liquid  by  heating  it,  and  the  transitions 
from  the  solid  to  the  liquid  state  by  the  alternate  abstraction 
and  addition  of  heat,  may  be  repeated  several  times ;  but  at 
length  the  gelatin  is  so  far  altered,  and,  apparently,  oxidized 
by  the  process,  that  it  no  longer  becomes  solid  on  cooling. 
Gelatin  in  solutions  too  weak  to  solidify  when  cold,  is  dis- 
tinguished by  being  precipitable  with  alcohol,  ether,  tannic 
acid,  and  bichloride  of  mercury,  and  not  precipitable  with  the 
ferrocyanide  of  potassium.  The  most  delicate  and  striking  of 
these  tests  is  the  tannic  acid,  which  is  conveniently  supplied 
in  an  infusion  of  oak-bark  or  gall-nuts;  it  will  detect  one  part 
of  gelatin  in  5000  of  water ;  and  if  the  solution  of  gelatin  be 
strong  it  forms  a  singularly  dense  and  heavy  precipitate,  which 
has  been  named  tanno-gelatin,  and  is  completely  insoluble  in 
water. 

Chondrin,  the   kind   of  gelatin  obtained   from  cartilages, 
agrees  with  gelatin  in  most  of  its  characters,  but  its  solution 


22      CHEMICAL   COMPOSITION   OF    HUMAN    BODY. 

solidifies  on  cooling  much  less  firmly,  and,  unlike  gelatin,  it  is 
precipitable  with  acetic  and  the  mineral  and  other  acids,  and 
with  alum,  persulphate  of  iron,  and  acetate  of  lead. 

Albuminous  substances,  or  proteids,  as  they  are  sometimes 
called,  exist  abundantly  in  the  human  body.  The  chief  among 
them  are  albumen,  fibrin,  casein,  syntonin,  myosin,and  globulin. 

Albumen  exists  in  most  of  the  tissues  of  the  body,  but  es- 
pecially in  the  nervous,  in  the  lymph,  chyle,  and  blood,  and 
in  many  morbid  fluids,  as  the  serous  secretions  of  dropsy,  pus, 
and  others.  In  the  human  body  it  is  most  abundant,  and 
most  nearly  pure,  in  the  serum  of  the  blood.  In  all  the  forms 
in  which  it  naturally  occurs,  it  is  combined  with  about  six  per 
cent,  of  fatty  matter,  phosphate  of  lime,  chloride  of  sodium, 
and  other  saline  substances.  Its  most  characteristic  property 
is,  that  both  in  solution  and  in  the  half-solid  state  in  which  it 
exists  in  white  of  egg,  it  is  coagulated  by  heat,  and  in  thus 
becoming  solid,  becomes  insoluble  in  water.  The  temperature 
required  for  the  coagulation  of  albumen  is  the  higher  the  less 
the  proportion  of  albumen  in  the  solution  submitted  to  heat. 
Serum  and  such  strong  solutions  will  begin  to  coagulate  at 
from  150°  to  170°,  and  these,  when  the  heat  is  maintained, 
become  almost  solid  and  opaque.  But  weak  solutions  require 
a  much  higher  temperature,  even  that  of  boiling,  for  their 
coagulation,  and  either  only  become  milky  or  opaline,  or  pro- 
duce flocculi  which  are  precipitated. 

Albumen,  in  the  state  in  which  it  naturally  occurs,  appears 
to  be  but  little  soluble  in  pure  water,  but  is  soluble  in  water 
containing  a  small  proportion  of  alkali.  In  such  solutions  it  is 
probably  combined  chemically  with  the  alkali ;  it  is  precip- 
itated from  them  by  alcohol,  nitric,  and  other  mineral  acids, 
by  ferrocyanide  of  potassium  (if  before  or  after  adding  it  the 
alkali  combined  with  the  albumen  be  neutralized),  by  bi- 
chloride of  mercury,  acetate  of  lead,  and  most  metallic  salts. 

Coagulated  albumen,  i.  e.,  albumen  made  solid  with  heat,  is 
soluble  in  solutions  of  caustic  alkali,  and  in  acetic  acid  if  it  be 
long  digested  or  boiled  with  it.  With  the  aid  of  heat,  also, 
strong  hydrochloric  acid  dissolves  albumen  previously  coag- 
ulated, and  the  solution  has  a  beautiful  purple  or  blue  color. 

Fibrin  is  found  most  abundantly  in  the  blood  and  the  more 
perfect  portions  of  the  lymph  and  chyle.  It  is  very  doubtful, 
however,  whether  fibrin,  as  such,  exists  in  these  fluids — whether, 
that  is  to  say,  it  is  not  itself  formed  at  the  moment  of  coagula- 
tion. (See  chapter  on  the  Blood.) 

If  a  common  clot  of  blood  be  pressed  in  fine  linen  while  a 
stream  of  water  flows  upon  it,  the  whole  of  the  blood-color  is 
gradually  removed,  and  strings  and  various  pieces  remain  of 


CASEIN — SYNTONIN  —  MYOSIN. 


23 


a  soft,  yet  tough,  elastic,  and  opaque-white  substance,  which 
consist  of  fibrin,  impure,  with  a  mixture  of  fatty  matter,  lymph- 
corpuscles,  shreds  of  the  membranes  of  red  blood-corpuscles, 
and  some  saline  substances.  Fibrin  somewhat  purer  than  this 
may  be  obtained  by  stirring  blood  while  it  coagulates,  and 
collecting  the  shreds  that  attach  themselves  to  the  instrument, 
or  by  retarding  the  coagulation,  and,  while  the  red  blood- 
corpuscles  sink,  collecting  the  fibrin  unmixed  with  them.  But 
in  neither  of  these  cases  is  the  fibrin  perfectly  pure. 

Chemically,  fibrin  and  albumen  can  scarcely  be  distin- 
guished ;  the  only  difference  apparently  being  that  fibrin  con- 
tains 1.5  more  oxygen  in  every  100  parts  than  albumen  does. 
Mr.  A.  H.  Smee  has,  indeed,  apparently  converted  albumen 
into  fibrin,  by  exposing  a  solution  to  the  prolonged  influence 
of  oxygen.  Nearly  all  the  changes,  produced  by  various 
agents,  in  coagulated  albumen,  may  be  repeated  with  coag- 
ulated fibrin,  with  no  greater  differences  of  result  than  may 
be  reasonably  ascribed  to  the  differences  in  the  mechanical 
properties  of  the  two  substances.  Of  such  differences  the  prin- 
cipal are,  that  fibrin  immersed  in  acetic  acid  swells  up  and 
becomes  transparent  like  gelatin,  while  albumen  undergoes 
no  such  apparent  change ;  and  that  deutoxide  of  hydrogen  is 
decomposed  when  in  contact  with  coagulated  fibrin,  but  not 
with  albumen. 

Casein,  which  is  said  to  be  albumen  in  combination  with 
soda,  exists  largely  in  milk,  and  forms  one  of  its  most  im- 
portant constituents. 

Syntonin  is  obtained  from  muscular  tissue,  both  of  the  striated 
and  organic  kind.  It  differs  from  ordinary  fibrin  in  several 
particulars,  especially  in  being  less  soluble  in  nitrate  and  car- 
bonate of  potash,  and  more  soluble  in  dilute  hydrochloric  acid. 

Myosin  is  the  substance  which  spontaneously  coagulates  in 
the  juice  of  muscle.  It  is  closely  allied  to  syntonin  ;  indeed, 
in  the  act  of  solution  in  dilute  acids,  it  is  converted  into  it. 

The  percentage  composition  of  albumen,  fibrin,  gelatin,  and 
chondrin,  is  thus  given  by  Mulder : 


Albumen. 

Fibrin. 

Gelatin. 

Chondrin. 

Carbon,      .... 

53.5 

527 

50.40 

49.97 

Hydrogen, 
Nitrogen,  .     . 

7.0 
15.5 

6.9 
15.4 

6.64 
18.34 

6.63 
14.44 

Oxygen,     .     . 
Sulphur,    .     . 

22.0 
1.6 

23.5 
1.2 

1    24.26 

\    28.58 
/      0.38 

Phosphorus,   . 

0.4 

0.3 

100.0 

100.0 

100.00 

100.00 

24      CHEMICAL   COMPOSITION    OF    HUMAN   BODY. 

Horny  Matter. — The  substance  of  the  horny  tissues,  includ- 
ing the  hair  and  nails  (with  whalebone,  hoofs,  and  horns), 
consists  of  an  albuminous  substance,  with  larger  proportions 
of  sulphur  than  albumen  and  fibrin  contain.  Hair  contains 
10  per  cent,  and  nails  6  to  8  per  cent,  of  sulphur. 

The  horny  substances,  to  which  Simon  applied  the  name  of 
keratin,  are  insoluble  in  water,  alcohol,  or  ether;  soluble  in 
caustic  alkalies,  and  sulphuric,  nitric,  and  hydrochloric  acids; 
and  not  precipitable  from  the  solution  in  acids  by  ferrocyanide 
of  potassium. 

Mucus,  in  some  of  its  forms,  is  related  to  these  horny  sub- 
stances, consisting,  in  great  part,  of  epithelium  detached  from 
the  surface  of  mucous  membrane,  and  floating  in  a  peculiar 
clear  and  viscid  fluid.  But  under  the  name  of  mucus,  several 
various  substances  are  included  of  which  some  are  morbid 
albuminous  secretions  containing  mucus  and  pus-corpuscles, 
and  others  consist  of  the  fluid  secretion  variously  altered,  con- 
centrated, or  diluted.  Mucus  contains  an  albuminous  sub- 
stance, termed  mucin.  It  differs  from  albumen  chiefly  in  not 
containing  sulphur. 

Pepsin  and  other  albuminous  ferments,  as  they  are  sometimes 
called,  will  be  described  in  connection  with  the  secretions  of 
which  they  are  the  active  principles.  And  the  various  color- 
ing matters,  as  of  the  blood,  bile,  &c.,  will  be  also  considered 
with  the  fluids  or  tissues  to  which  they  belong. 

Besides  the  above-mentioned  organic  nitrogenous  compounds, 
other  substances  are  formed  in  the  living  body,  chiefly  by  de- 
composition of  nitrogenous  materials  of  the  food  and  of  the 
tissues,  which  must  be  reckoned  rather  as  temporary  constitu- 
ents than  essential  component  parts  of  the  body;  although 
from  the  continual  change,  which  is  a  necessary  condition  of 
life,  they  are  always  to  be  found  in  greater  or  less  amount. 
Examples  of  these  are  urea,  uric  and  hippuric  acids,  creatin, 
creatinin,  leucin,  and  many  others. 

Such  are  the  chief  organic  substances  of  which  the  human 
body  is  composed.  It  must  not  be  supposed,  however,  that 
they  exist  naturally  in  a  state  approaching  that  of  chemical 
purity.  All  the  fluids  and  tissues  of  the  body  appear  to  con- 
sist, chemically  speaking,  of  mixtures  of  several  of  these  prin- 
ciples, together  with  saline  matters.  Thus,  for  example,  a 
piece  of  muscular  flesh  would  yield  fibrin,  albumen,  gelatin, 
fatty  matters,  salts  of  soda,  potash,  lime,  magnesia,  iron,  and 
other  substances,  such  as  creatin,  which  appear  passing  from 
the  organic  towards  the  inorganic  state.  This  mixture  of  sub- 
stances may  be  explained  in  some  measure  by  the  existence  of 
many  different  structures  or  tissues  in  the  muscles ;  the  gelatin 


WATER  —  POTASH  —  SODA.  25 

may  be  referred  principally  to  the  cellular  tissue  between  the 
fibres,  the  fatty  matter  to  the  adipose  tissue  in  the  same  posi- 
tion, and  part  of  the  albumen  to  the  blood  and  the  fluid  by 
which  the  tissue  is  kept  moist.  But,  beyond  these  general 
statements,  little  can  be  said  of  the  mode  in  which  the  chemi- 
cal compounds  are  united  to  form  an  organized  structure;  or 
of  how,  in  any  organic  body,  the  several  incidental  substances 
are  combined  with  those  which  are  essential. 

The  inorganic  matters  which  exist  as  such  in  the  human 
body  are  numerous. 

Water  forms  a  large  proportion,  probably  more  than  two- 
thirds  of  the  weight  of  the  whole  body. 

Phosphorus  occurs  in  combination, — as  in  the  neutral  phos- 
phate of  sodium  in  the  blood  and  saliva,  the  acid  phosphates 
of  the  muscles  and  urine,  the  basic  phosphates  of  calcium  and 
magnesium  in  the  bones  and  teeth. 

Sulphur  is  present  chiefly  in  the  sulphocyanide  of  potassium 
of  the  saliva,  and  in  the  sulphates  of  the  urine  and  sweat. 

A  very  small  quantity  of  silica  exists,  according  to  Berze- 
lius,  in  the  urine,  and,  according  to  others,  in  the  blood. 
Traces  of  it  have  also  been  found  in  bones,  in  hair,  and  in 
some  other  parts  of  the  body. 

Chlorine  is  abundant  in  combination  with  sodium,  potas- 
sium, and  other  bases  in  all  parts,  fluid  as  well  as  solid,  of  the 
body.  A  minute  quantity  of  fluorine  in  combination  with 
calcium  has  been  found  in  the  bones,  teeth,  and  urine. 

Potassium  and  sodium  are  constituents  of  the  blood  and  all 
the  fluids,  in  various  quantities  and  proportions.  They  exist 
in  the  form  of  chlorides,  sulphates,  and  phosphates,  and  prob- 
ably, also,  in  combination  with  albumen,  or  certain  organic 
acids.  Liebig,  in  his  work  on  the  Chemistry  of  Food,  has 
shown  that  the  juice  expressed  from  muscular  flesh  always 
contains  a  much  larger  proportion  of  potash-salts  than  of  soda- 
salts;  while  in  the  blood  and  other  fluids,  except  the  milk,  the 
latter  salts  always  preponderate  over  the  former ;  so  that,  for 
example,  for  every  100  parts  of  soda-salts  in  the  blood  of  the 
chicken,  ox,  and  horse,  there  are  only  40.8,  5.9,  and  9.5  parts 
of  potash-salts ;  but  for  every  100  parts  of  soda-salts  in  their 
muscles,  there  are  381,  279,  and  285  parts  of  potash-salts. 

The  salts  of  calcium  are  by  far  the  most  abundant  of  the 
earthy  salts  found  in  the  human  body.  They  exist  in  the 
lymph,  chyle,  and  blood,  in  combination  with  phosphoric  acid, 
the  phosphate  of  calcium  being  probably  held  in  solution  by 
the  presence  of  phosphate  of  sodium.  Perhaps  no  tissue  is 
wholly  void  of  phosphate  of  calcium;  but  its  especial  seats  are 
the  bones  and  teeth,  in  which,  together  with  carbonate  and 


26    STRUCTURAL  COMPOSITION  OF   HUMAN   BODY. 

fluoride  of  calcium,  it  is  deposited  in  minute  granules,  in  a 
peculiar  compound,  named  bone-earth,  containing  51.55  parts 
of  lime,  arid  48.45  of  phosphoric  acid.  Phosphate  of  calcium, 
probably  the  neutral  phosphate,  is  also  found  in  the  saliva, 
milk,  bile,  and  most  other  secretions,  and  acid  phosphate  in 
the  urine,  and,  according  to  Blondlot,  in  the  gastric  fluid. 

Magnesium  appears  to  be  always  associated  with  calcium, 
but  its  proportion  is  much  smaller,  except  in  the  juice  ex- 
pressed from  muscles,  in  the  ashes  of  which  magnesia  prepon- 
derates over  lime. 

The  especial  place  of  iron  is  in  the  haemoglobin,  the  color- 
ing-matter of  the  blood,  of  which  a  further  account  will  be 
given  with  the  chemistry  of  the  blood.  Peroxide  of  iron  is 
found,  in  very  small  quantities,  in  the  ashes  of  bones,  muscles, 
and  many  tissues,  and  in  lymph  and  chyle,  albumen  of  serum, 
fibrin,  bile,  and  other  fluids ;  and  a  salt  of  iron,  probably  a 
phosphate,  exists  in  considerable  quantity  in  the  hair,  black 
pigment,  and  other  deeply  colored  epithelial  or  horny  sub- 
stances. 

Aluminium,  Manganese,  Copper,  and  Lead. — It  seems  most 
likely  that  in  the  human  body,  copper,  manganesium,  alumin- 
ium, and  lead  are  merely  accidental  elements,  which,  being 
taken  in  minute  quantities  with  the  food,  and  not  excreted  at 
once  with  the  faeces,  are  absorbed  and  deposited  in  some  tissue 
or  organ,  of  which,  however,  they  form  no  necessary  part.  In 
the  same  manner,  arsenic,  being  absorbed,  may  be  deposited 
in  the  liver  and  other  parts. 


CHAPTER  III. 

STRUCTURAL   COMPOSITION   OF   THE    HUMAN   BODY. 

IN  the  investigation  of  the  structural  composition  of  the 
human  body,  it  will  be  well  to  consider  in  the  first  place,  what 
are  the  simplest  anatomical  elements  which  enter  into  its  for- 
mation, and  then  proceed  to  examine  those  more  complicated 
tissues  which  are  produced  by  their  union. 

It  may  be  premised,  that  in  all  the  living  parts  of  all  living 
things,  animal  and  vegetable,  there  is  invariably  to  be  dis- 
covered, entering  into  the  formation  of  their  anatomical  ele- 
ments, a  greater  or  less  amount  of  a  substance,  which,  in 
chemical  composition  and  general  characters,  is  indistiuguish- 


PROTOPLASM.  27 

able  from  albumen.  As  it  exists  in  a  living  tissue  or  organ,  it 
differs  essentially  from  mere  albumen  in  the  fact  of  its  possess- 
ing the  power  of  growth,  development,  and  the  like ;  but  in 
chemical  composition  it  is  identical  with  it. 

This  albuminous  substance  has  received  various  names  ac- 
cording to  the  structures  in  which  it  has  been  found,  and  the 
theory  of  its  nature  and  uses  which  may  have  presented  itself 
most  strongly  to  the  minds  of  its  observers.  In  the  bodies  of 
the  lowest  animals,  as  the  Rhizopoda  or  Gregarinida,  of  which 
it  forms  the  greater  portion,  it  has  been  called  "sarcode,"  from 
its  chemical  resemblance  to  the  flesh  of  the  higher  animals. 
When  discovered  in  vegetable  cells,  and  supposed  to  be  the 
prime  agent  in  their  construction,  it  was  termed  "protoplasm." 
As  the  presumed  formative  matter  in  animal  tissues  it  was 
called  "  blastema ;"  and,  with  the  belief  that  wherever  found, 
it  alone  of  all  matters  has  to  do  with  generation  and  nutrition, 
Dr.  Beale  has  surnamed  it  "  germinal  matter." 

So  far  as  can  be  discovered,  there  is  no  difference  in  chemical 
composition  between  the  protoplasm  of  one  part  or  organism 
and  that  of  another.  The  movements  which  can  be  seen  in 
certain  vegetable  cells  apparently  belong  to  a  substance  which 
is  identical  in  composition  with  that  which  constitutes  the 
greater  portion  of  the  bodies  of  the  lowest  animals,  and  which 
is  present  in  greater  or  less  quantity  in  all  the  living  parts  of 
the  highest.  So  much  appears  to  be  a  fact ; — that  in  all  living 
parts  there  exists  an  albuminous  substance,  in  which  in  favor- 
able cases  for  observation  in  vegetable  and  the  lower  animal 
organisms,  there  can  be  noticed  certain  phenomena  which  are 
not  to  be  accounted  for  by  physical  impressions  from  without, 
but  are  the  result  of  inherent  properties  we  call  vital.  For 
example,  if  a  hair  of  the  Tradescantia  Virginica,  or  of  many 
other  plants,  be  examined  under  the  microscope,  there  is  seen 
in  each  individual  cell  a  movement  of  the  protoplasmic  con- 
tents in  a  certain  definite  direction  around  the  interior  of  the 
cell.  Each  cell  is  a  closed  sac  or  bag,  and  its  contents  are 
therefore  quite  cut  off  from  the  direct  influence  of  any  motive 
power  from  without.  The  motion  of  the  particles,  moreover, 
in  a  circuit  around  the  interior  of  the  cell,  precludes  the  notion 
of  its  being  due  to  any  other  than  those  molecular  changes 
which  we  call  vital.  Again,  in  the  lowest  animals,  whose 
bodies  resemble  more  than  anything  else  a  minute  mass  of 
jelly,  and  which  appear  to  be  made  up  almost  solely  of  this 
albuminous  protoplasm,  there  are  movements  in  correspondence 
with  the  needs  of  the  organism,  whether  with  respect  to  seiz- 
ing food  or  any  other  purpose,  which  are  unaccountable  accord- 
ing to  any  known  physical  laws,  and  can  only  be  called  vital. 


28   STRUCTURAL  COMPOSITION  OF  HUMAN   BODY. 

In  many,  too,  there  is  a  kind  of  molecular  current,  exactly 
resembling  that  which  is  seen  in  a  vegetable  cell. 

In  the  higher  animals,  phenomena  such  as  these  are  so  sub- 
ordinate to  the  more  complex  manifestations  of  life  that  they 
are  apt  to  be  overlooked  ;  but  they  exist  nevertheless.  The 
mere  nutrition  of  each  part  of  the  body  in  man  or  in  the 
higher  animals,  is  performed  after  a  fashion  which  is  strictly 
analogous  to  that  which  holds  good  in  the  case  of  a  vegetable 
cell,  or  a  rhizopod  ;  or,  in  other  words,  the  life  of  each  anatomi- 
cal element  in  a  complex  structure,  like  the  human  body,  re- 
sembles very  closely  the  life  of  what  in  the  lowest  organisms 
constitutes  the  whole  being.  For  example,  the  thin  scaly 
covering  or  epidermis,  which  forms  the  outer  part  of  a  man's 
skin,  is  made  up  of  minute  cells,  which,  when  living,  are  com- 
posed in  part  of  protoplasm,  and  which  are  continually  wear- 
ing away  and  being  replaced  by  new  similar  elements  from 
beneath  ;  and  this  process  of  quick  waste  and  repair  could  only 
take  place  under  the  very  complex  conditions  of  nutrition 
which  exist  in  man.  One  working  part  of  the  organism  of  an 
animal  is  so  inextricably  interwoven  with  that  of  another, 
that  any  want  or  defect  in  one,  is  soon  or  immediately  felt  by 
the  whole ;  and  the  epidermis,  which  only  subserves  a  mechani- 
cal function,  would  be  altered  very  soon  by  any  defect  in  the 
more  essential  parts  concerned  in  circulation,  respiration,  &c. 
But  if  we  take  simply  the  life  history  of  one  of  the  small  cells 
which  constitute  the  epidermis,  we  find  that  it  absorbs  nour- 
ishment from  the  parts  around,  grows,  and  develops  in  a 
manner  analogous  to  that  which  belongs  to  a  cell  which  con- 
stitutes part  of  a  vegetable  structure,  or  even  a  cell  which 
by  itself  forms  an  independent  being. 

Remembering,  however,  the  invariable  presence  of  a  living 
albuminous  matter  or  protoplasm  of  apparently  identical  com- 
position in  all  living  tissues,  animal  and  vegetable,  we  must 
not  forget  that  its  relations  to  the  parts  with  which  it  is  in- 
corporated are  still  very  doubtfully  known ;  and  all  theories 
concerning  it  must  be  considered  only  tentative  and  of  uncer- 
tain stability. 

Among  the  anatomical  elements  of  the  human  body,  some 
appear,  even  with  the  help  of  the  best  microscopic  apparatus, 
perfectly  uniform  and  simple :  they  show  no  trace  of  struc- 
ture, i.  e.,  of  being  composed  of  definitely  arranged  dissimilar 
parts.  These  are  named  simple,  structureless,  or  amorphous 
substances.  Such  is  the  simple  membrane  which  forms  the 
walls  of  most  primary  cells,  of  the  finest  gland-ducts,  and  of 
the  sarcolemma  of  muscular  fibre ;  and  such  is  the  membrane 
enveloping  the  vitreous  humor  of  the  eye.  Such  also,  having 


NUCLEI.  29 

a  dimly  granular  appearance,  but  no  really  granular  struc- 
ture, is  the  intercellular  substance  of  the  so-called  hyaline  car- 
tilage. 

In  the  parts  which  present  determinate  structure,  certain 
primary  forms  may  be  distinguished,  which,  by  their  various 
modifications  and  modes  of  combination  make  up  the  tissues 
and  organs  of  the  body.  Such  are,  1.  Granules  or  molecules, 
the  simplest  and  minutest  of  the  primary  forms.  They  are 
particles  of  various  sizes,  from  immeasurable  minuteness  to  the 
10,000th  of  an  inch  in  diameter ;  of  various  and  generally  un- 
certain composition,  but  usually  so  affecting  light  transmitted 
through  them,  that  at  different  focal  distances  their  centre,  or 
margin,  or  whole  substance,  appears  black.  From  this  char- 
acter, as  well  as  from  their  low  specific  gravity  (for  in  micro- 
scopic examinations  they  always  appear  lighter  than  water), 
and  from  their  solubility  in  ether  when  they  can  be  favorably 
tested,  it  is  probable  that  most  granules  are  formed  of  fatty  or 
oily  matter  ;  or,  since  they  do  not  coalesce  as  minute  drops 
of  'oil  would,  that  they  are  particles  of  oil  coated  over  with 
albumen  deposited  on  them  from  the  fluid  in  which  they  float. 
In  any  fluid  that  is  not  too  viscid,  they  exhibit  the  phenome- 
non of  molecular  motion,  shaking  and  vibrating  incessantly, 
and  sometimes  moving  through  the  fluid,  probably,  in  great 
measure,  under  the  influence  of  external  vibration. 

Granules  may  be  either  free,  as  in  milk,  chyle,  milky  serum, 
yolk-substance,  and  most  tissues  containing  cells  with  granules ; 
or  inclosed,  as  are  the  granules  in  nerve-corpuscles,  gland-cells, 
and  epithelium-cells,  the  pigment  granules  in  the  pigmentum 
nigrum  and  medullary  substance  of  the  hair ;  or  imbedded,  as 
are  the  granules  of  phosphate  and  carbonate  of  lime,  in  bones 
and  teeth. 

2.  Nuclei,  or  cytoblasts  (Fig.  1,  6),  appear  to  be  the  simplest 
elementary  structures,  next  to  granules.  They  were  thus 
named  in  accordance  with  the  hypothesis  that  they  are  always 
connected  with  cells,  or  tissues  formed  from  cells,  and  that  in 
the  development  of  these,  each  nucleus  is  the  germ  or  centre 
around  which  the  cell  is  formed.  The  hypothesis  is  only  par- 
tially true,  but  the  terms  based  on  it  are  too  familiarly  ac- 
cepted to  make  it  advisable  to  change  them  till  some  more 
exact  and  comprehensive  theory  is  formed. 

Of  the  corpuscles  called  nuclei  some  are  minute  cellules  or 
vesicles,  with  walls  formed  of  simple  membrane,  inclosing 
often  one  or  more  particles,  like  minute  granules,  called  nu- 
cleoli  (Fig,  1,  c).  Other  nuclei,  again,  appear  to  be  simply 
small  masses  of  protoplasm,  with  no  trace  of  vesicular  struc- 
ture. 


30   STRUCTURAL  COMPOSITION  OF   HUMAN  BODY. 

One  of  the  most  general  characters  of  the  nucleus,  and  the 
most  useful  in  microscopic  examinations,  is,  that  it  is  neither 
dissolved  nor  made  transparent  by  acetic  acid,  but  acquires, 
when  that  fluid  is  in  contact  with  it,  a  darker  and  more  dis- 
tinct outline.  It  is  commonly,  too,  the  part  of  the  mature 
cell  which  is  capable  of  being  stained  by  an  ammoniacal  solu- 
tion of  carmine — the  test,  it  may  be  remarked,  by  which,  ac- 
cording to  Dr.  Beale,  protoplasm  or  germinal  matter  may  be 
always  known. 

Nuclei  may  be  either  free  or  attached.  Free  nuclei  are  such 
as  either  float  in  fluid,  like  those  in  some  of  the  secretions, 
which  appear  to  be  derived  from  the  secreting  cells  of  the 
glands,  or  lie  loosely  imbedded  in  solid  substance,  as  in  the 
gray  matter  of  the  brain  and  spinal  cord,  and  most  abun- 
dantly in  some  quickly-growing  tumors.  Attached  nuclei  are 
either  closely  imbedded  in  homogeneous  pellucid  substance, 
as  in  rudimental  cellular  tissue ;  or  are  fixed  on  the  surface  of 
fibres,  as  on  those  of  organic  muscle  and  organic  nerve-fibres ; 
or  are  inclosed  in  cells,  or  in  tissues  formed  by  the  extension 
or  junction  of  cells.  Nuclei  inclosed  in  cells  appear  to  be  at- 
tached to  the  inner  surface  of  the  cell-wall,  projecting  into  the 
cavity.  Their  position  in  relation  to  the  centre  or  axis  of  the 
cell  is  uncertain  ;  often  when  the  cell  lies  on  a  flat  or  broad 
surface,  they  appear  central,  as  in  blood-corpuscles,  epithelium- 
cells,  whether  tessellated  or  cylindrical ;  but,  perhaps,  more 
often  their  position  has  no  regular  relation  to  the  centre  of 
the  cell.  In  most  instances,  each  cell  contains  only  a  single 
nucleus;  but  in  cartilage,  especially  when  it  is  growing  or 
ossifying,  two  or  more  nuclei  in  each  cell  are  common ;  and 
the  development  of  new  cells  is  often  effected  by  a  division  or 
multiplication  of  nuclei  in  the  cavity  of  a  parent  cell ;  as  in 
the  primary  blood-cells  of  the  embryo,  in  the  germinal  vesicle, 
and  others. 

When  cells  extend  and  coalesce,  so  that  their  walls  form 
tubes  or  sheaths,  the  nuclei  commonly  remain  attached  to  the 
inner  surface  of  the  wall.  Thus  they  are  seen  imbedded  in 
the  walls  of  the  minutest  capillary  bloodvessels  of,  for  exam- 
ple,' the  retina  and  brain ;  in  the  sarcolemma  of  transversely 
striated  muscular  fibres ;  and  in  minute  gland-tubes. 

Nuclei  are  most  commonly  oval  or  round,  and  do  not  gen- 
erally conform  themselves  to  the  diverse  shapes  which  the 
cells  assume ;  they  are  altogether  less  variable  elements,  even 
in  regard  to  size,  than  the  cells  are,  of  which  fact  one  may  see 
a  good  example  in  the  uniformity  of  the  nuclei  in  cells  so  mul- 
tiform as  those  of  epithelium.  But  sometimes  they  appear  to 
be  developed  into  filaments,  elongating  themselves  and  becom- 


CELLS.  31 

ing  solid,  and  uniting  end  to  end  for  greater  length,  or  by  lat- 
eral branches  to  form  a  network.  So,  according  to  Henle,  are 
formed  the  filaments  of  the  striated  and  fenestrated  coats  of 
arteries ;  and  according  to  Beale,  the  so-called  connective-tis- 
sue corpuscles  are  to  be  considered  branched  nuclei,  formed 
of  protoplasm  or  germinal  matter. 

3.  Cells. — The  word  "  cell "  of  course  implies  strictly  a  hollow 
body,  and  the  term  was  a  sufficiently  good  one  when  all  so- 
called  cells  were  considered  to  be  small  bags  with  a  membra- 
nous envelope,  and  more  or  less  liquid  contents.  Many  bodies, 
however,  which  are  still  called  cells  do  not  answer  to  this  de- 
scription, and  the  term,  therefore,  if  taken  in  its  literal  signifi- 
cation, is  very  apt  to  lead  astray,  and,  indeed,  very  frequently 
does  so.  It  is  too  widely  used,  however,  to  be  given  up,  at 
least  for  the  present,  and  we  must  therefore  consider  the  term 
to  indicate,  either  a  membranous  closed,  bag  with  more  or  less 
liquid  contents,  and  almost  always  a  nucleus  ;  or  a  small  semi- 
solid  mass  of  protoplasm,  with  no  more  definite  boundary-wall 
than  such  as  has  been  formed  by  a  condensation  of  its  outer 
layers,  but  with,  most  commonly,  a  small  granular  substance 
in  the  centre,  called,  as  in  the  first  place,  a  nucleus.  In  both 
cases  the  nucleus  may  contain  a  nucleolus.  Fat-cells  (Fig.  11) 
are  examples  of  the  first  kind  of  cells ;  white  blood-corpuscles 
(Fig.  26)  of  the  second. 

The  cell-wall,  when  there  is  one,  never  presents  any  appear- 
ance of  structure :  it  appears  sometimes  to  be  an  albuminous 
substance ;  sometimes  a  horny  matter,  as  in  thick  and  dried 
cuticle.  In  almost  all  cases  (the  dry  cells  of  horny  tissue, 
perhaps,  alone  excepted)  the  cell-wall  is  made  transparent  by 
acetic  acid,  which  also  penetrates  into  the  interior  and  distends 
it,  so  that  it  can  hardly  be  discerned.  But  in  such  cases  the 
cell-wall  is  usually  not  dissolved ;  it  may  be  brought  into 
view  again  by  merely  neutralizing  the  acid  with  soda  or 
potash. 

The  simplest  shape  of  cells,  and  that  which  is  probably  the 
normal  shape  of  the  primary  cell,  is  oval  or  spheroidal,  as  in 
cartilage-cells  and  lymph-corpuscles ;  but  in  many  instances 
they  are  flattened  and  discoid,  as  in  the  red  blood-corpuscles 
(Fig.  26) ;  or  scale-like,  as  in  the  epidermis  and  tessellated 
epithelium  (Fig.  2).  By  mutual  pressure  they  may  become 
many-sided,  as  are  most  of  the  pigment-cells  of  the  choroidal 
pigmentum  nigrum  (Fig.  12),  and  those  in  close-textured 
adipose  tissue ;  they  may  assume  a  conical  or  cylindriform  or 
prismatic  shape,  as  in  the  varieties  of  cylinder-epithelium 
(Fig.  4) ;  or  be  caudate,  as  in  certain  bodies  in  the  spleen ; 
they  may  send  out  exceedingly  fine  processes  in  the  form  of 


32   STRUCTURAL  COMPOSITION  OF   HUMAN   BODY. 

vibratile  cilia  (Fig.  6),  or  larger  processes,  with  which  they 
become  stellate,  or  variously  caudate,  as  in  some  of  the  rami- 
fied pigment-cells  of  the  choroid  coat  of  the  eye  (Fig.  13). 

The  contents  of  all  living  cells,  including  the  nucleus,  are 
formed  in  a  greater  or  less  degree  of  protoplasm — less  as  the 
cell  grows  older.  But,  besides,  cells  contain  matters  almost 
infinitely  various,  according  to  the  position,  office,  and  age  of 
the  cell.  In  adipose  tissue  they  are  the  oily  matter  of  the  fat ; 
in  gland-cells,  the  contents  are  the  proper  substance  of  the 
secretion,  bile,  semen,  &c.,  as  the  case  may  be ;  in  pigment-cells 
they  are  the  pigment-granules  that  give  the  color ;  and  in  the 
numerous  instances  in  which  the  cell-contents  can  be  neither 
seen  because  they  are  pellucid,  nor  tested  because  of  their 
minute  quantity,  they  are  yet,  probably,  peculiar  in  each  tissue, 
and  constitute  the  greater  part  of  the  proper  substance  of  each. 
Commonly,  when  the  contents  are  pellucid,  they  contain  gran- 
ules which  float  in  them ;  and  when  water  is  added,  and  the 
contents  are  diluted,  the  granules  display  an  active  molecular 
movement  within  the  cavity  of  the  cell.  Such  a  movement 
may  be  seen  by  adding  water  to  mucus,  or  granulation-corpus- 
cles, or  to  those  of  lymph.  In  a  few  cases,  the  whole  cavity 
of  the  cell  is  filled  with  granules :  it  is  so  in  yolk-cells  and 
milk-corpuscles,  in  the  large  diseased  corpuscles  often  found 
among  the  products  of  inflammation,  and  in  some  cells  when 
they  are  the  seat  of  extreme  fatty  degeneration.  All  cells 
containing  abundant  granules  appear  to  be  either  lowly  organ- 
ized, as  for  nutriment,  e.  g.,  yolk-cells,  or  degenerate,  e.  g., 
granule-cells  of  inflammation,  or  of  mucus.  The  peculiar  con- 
tents of  cells  may  be  often  observed  to  accumulate  first  around 
or  directly  over  the  nuclei,  as  in  the  cells-  of  black  pigment,  in 
those  of  melanotic  tumors,  and  in  those  of  the  liver  during  the 
retention  of  bile. 

Intercellular  substance  is  the  material  in  which,  in  certain 
tissues,  the  cells  are  imbedded.  Its  quantity  is  very  variable. 
In  the  finer  epithelia,  especially  the  columnar  epithelium  on 
the  mucous  membrane  of  the  intestines,  it  can  be  just  seen  fill- 
ing the  interstices  of  the  close-set  cells ;  here  it  has  no  appear- 
ance of  structure.  In  cartilage  and  bone,  it  forms  a  large 
portion  of  the  whole  substance  of  the  tissue,  and  is  either  hom- 
ogenous and  finely  granular  (Fig.  14),  or  osseous,  or,  as  in 
fibro-cartilage,  resembles  fine  fibrous  tissue  (Fig.  15).  In  some 
cases  the  cells  are  very  loosely  connected  with  the  intercellular 
substance,  and  may  be  nearly  separated  from  it,  as  in  fibro-car- 
tilage; but  in  some  their  walls  seem  amalgamated  with  it. 

The  foregoing  may  be  regarded  as  the  simplest  and  the  near- 
est to  the  primary  forms  assumed  in  the  organization  of  animal 


TUBULES.  33 

matter;  as  the  states  into  which  this  passes  in  becoming  a  solid 
tissue  living  or  capable  of  life.  By  the  further  development 
of  tissue  thus  far  organized,  higher  or  secondary  forms  are  pro- 
duced, which  it  will  be  sufficient  in  this  place  merely  to  enu- 
merate. Such  are, 

4.  Filaments,  or  Fibrils. — Threads  of  exceeding  fineness,  from 
770-J  Q0th  of  an  inch  upwards.     Such  filaments  are  cylindriform, 
as  are  those  of  the  striated  muscular  and  the  fibro-cellular  or 
areolar  tissue  (Fig.  8) ;  or  flattened,  as  are  those  of  the  organic 
muscles.     Filaments  usually  lie  in  parallel  fasciculi,  as  in  mus- 
cular and  tendinous  tissues ;  but  in  some  instances  are  matted 
or  reticular  with  branches  and  intercommunication,  as  are  the 
filaments  of  the  middle  coat,  and  of  the  longitudinally-fibrous 
coat  of  arteries ;  and,  in  other  instances,  are  spirally  wound,  or 
very  tortuous,  as  in  the  common  fibro-cellular  tissue  (Fig.  9). 

5.  Fibres  in  the  instances  to  which  the  name  is  commonly 
applied  are  larger  than  filaments  or  fibrils,  but  are  by  no  es- 
sential general  character  distinguished  from  them.'    The  flat- 
tened band-like  fibres  of  the  coarser  varieties  of  organic  muscle 
or  elastic  tissue  (Fig.  10)  are  the  simplest  examples  of  this 
form" ;  the  toothed  fibres  of  the  crystalline  lens  are  more  com- 
plex; and  more  compound,  so  as  hardly  to  permit  of  being 
classed  as  elementary  forms,  are  the  striated  muscular  fibres, 
which  consist  of  bundles  of  filaments  inclosed  in  separate  mem- 
branous sheaths,  and  the  cerebro-spinal  nerve-fibres,  in  which 
similar  sheaths  inclose  apparently  two  varieties  of  nerve-sub- 
stance. 

6.  Tubules  are  formed  of  simple  or  structureless  membrane, 
such  as  the  investing  sheaths  of  striated  muscular  and  cerebro- 
spinal  nerve-fibres,  and  the  basement-membrane  or  proper  wall 
of  the  fine  ducts  of  secreting  glands;  or  they  may  be  formed, 
as  in  the  case  of  the  minute  capillary  lymph  and  bloodvessels, 
by  the  apposition,  edge  to  edge,  in  a  single  layer,  of  variously 
shaped  flattened  cells  (Fig.  48). 

With  these  simple  materials,  the  various  parts  of  the  body 
are  built  up;  the  more  elementary  tissues  being,  so  to  speak, 
first  compounded  of  them ;  while  these  again  are  variously 
mixed  and  interwoven  to  form  more  intricate  combinations. 
Thus  are  constructed  epithelium  and  its  modifications,  con- 
nective tissue,  fat,  cartilage,  bone,  the  fibres  of  muscle  and 
nerve,  &c. ;  and  these  again,  with  the  more  simple  structures 
before  mentioned,  are  used  as  materials  wherewith  to  form  ar- 
teries, veins,  and  lymphatics,  secreting  and  vascular  glands, 
lungs,  heart,  liver,  and  other  parts  of  the  body. 


34 


ELEMENTARY    TISSUES. 


CHAPTER  IV.1 


STRUCTURE   OF   THE   ELEMENTARY   TISSUES. 

Epithelium. 

ONE  of  the  simplest  of  the  elementary  structures  of  which 
the  human  body  is  made  up,  is  that  which  has  received  the 
name  of  Epithelium.  Composed  of  nucleated  cells  which  are 
arranged  most  commonly  in  the  form  of  a  continuous  mem- 
brane, it  lines  the  free  surfaces  both  of  the  inside  and  outside 
of  the  body,  and  its  varieties,  with  one  exception,  have  been 
named  after  the  shapes  which  the  individual  cells  in  different 
parts  assume.  Classified  thus,  Epithelium  presents  itself  under 
four  principal  forms,  the  characters  of  each  of  which  are  dis- 
tinct enough  in  well-marked  examples;  but  when,  as  frequently 
happens,  a  continuous  surface  possesses  at  different  parts  two 
or  more  different  epithelia,  there  is  a  very  gradual  transition 
from  one  to  the  other. 

1.  The  first  and  most  common  variety  is  the  squamous  or 
tessellated  epithelium  (Figs.  1  and  2)  which  is  composed  of  flat, 


FIG.  1. 


FIG.  2. 


FIG.  1.  Fragment  of  epithelium  from  a  serous  membrane  (peritoneum) ;  magnified 
410  diameters,  a,  cell;  b,  nucleus;  c,  nucleoli  (Henle). 

FIG.  2.  Epithelium  scales  from  the  inside  of  the  mouth ;  magnified  260  diameters 
(Henle). 

oval,  roundish,  or  polygonal  nucleated  cells,  of  various  size, 
arranged  in  one,  or  in  many  superposed  layers.     Arranged  in 

1  The  following  chapter,  containing  aw  outline-description  of  the 
elementary  tissues,  has  been  inserted  for  the  convenience  of  students. 
For  a  much  fuller  and  better  account,  the  reader  may  be  referred  to 
Dr.  Sharpey's  admirable  descriptions  in  Quain's  Anatomy. 


EPITHELIUM. 


35 


several  superposed  layers  this  form  of  epithelium  covers  the 
skin,  where  it  is  called  the  Epidermis,  and  is  spread  over  the 
mouth,  pharynx,  and  oesophagus,  the  conjunctiva  covering  the 
eye,  the  vagina,  and  entrance  of  the  urethra  in  both  sexes; 
while,  as  a  single  layer  the  same  kind  of  epithelium  lines  the 
interior  of  most  of  the  serous  and  synovial  sacs,  and  of  the 
heart,  bloodvessels,  and  lymphvessels. 

2.  Another  variety  of  epithelium  named  spheroidal,  from 
the  usually  more  or  less  rounded  outline  of  the  cells  composing 
it  (d,  Fig.  3),  is  found  chiefly  lining  the  interior  of  the  ducts 
of  the  compound  glands,  and  more  or  less  completely  filling 
the  small  sacculations  or  acini,  in  which  they  terminate.  It 
commonly  indeed  occupies  the  true  secreting  parts  of  all 
glands,  and  hence  is  sometimes  called  glandular  epithelium 


The  gastric  glands  of  the  human  stomach  (magnified),  a,  deep  part  of  a  pyloric 
gastric  gland  (from  Kolliker);  the  cylindrical  epithelium  is  traceable  to  the  cseeal 
extremities,  b  and  c,  cardiac  gastric  glands  (from  Allen  Thomson);  ft,  vertical  sec- 
tion of  a  small  portion  of  the  mucous  membrane  with  the  glands  magnified  30  diame- 
ters; c,  deeper  portion  of  one  of  the  glands,  magnified  Go  diameters,  showing  a  slight 
division  of  the  tubes,  and  a  sacculated  appearance  produced  by  the  large  glandular 
cells  within  them ;  d,  cellular  elements  of  the  cardiac  glands  magnified  230  diameters. 

(b,  c,  and  d,  Fig.  3).  Often,  from  mutual  pressure,  the  cells 
acquire  a  polygonal  outline.  From  the  fact,  however,  of  the 
term  spheroidal  epithelium  being  a  generic  one  for  almost  all 
gland-cells,  the  shapes  and  sizes  of  the  cells  composing  this 
variety  of  epithelium  are,  as  might  be  expected,  very  diverse 
in  different  parts  of  the  body. 

3.  The  third  variety  is  the  cylindrical  or  columnar  epithelium 
(Figs.  4  and  5),  which  extends  from  the  cardiac  orifice  of  the 


36 


ELEMENTARY    TISSUES. 


stomach  along  the  whole  of  the  digestive  canal  to  the  anus, 
and  lines  the  principal  gland-ducts  which  open  upon  the  mucous 


FIG.  4. 


Cylindrical  epithelium  from  intestinal  villus  of  a  rabbit;  magnified  300  diameters 
(from  Kolliker). 

surface  of  this  tract,  sometimes  throughout  their  whole  extent 
(a.  Fig.  3),  but  in  some  cases  only  at  the  part  nearest  to  the 
orifice  (b  and  c).  It  is  also  found  in  the  gall-bladder  and  in 
the  greater  portion  of  the  urethra,  and  in  some  other  parts,  as 
the  duct  of  the  parotid  gland  and  of  the  testicle.  It  is  com- 
posed of  oblong  cells  closely  packed,  and  placed  perpendicu- 
larly to  the  surface  they  cover,  their  deeper  or  attached  ex- 
tremities being  most  commonly  smaller  than  those  which  are 
free.  Each  of  such  cells  incloses,  at  nearly  mid  distance  be- 
tween its  base  and  apex,  a  flat  nucleus  with  nucleoli  (B,  Fig.  5) ; 


FIG.  5. 


Cylinders  of  the  intestinal  epithelium  (after  Henle) :  B,  from  the  jejunum ;  c,  cyl- 
inders of  the  intestinal  epithelium  as  seen  when  looking  on  their  free  extremities ; 
D,  ditto,  as  seen  on  a  transverse  section  of  a  villus. 

the  nuclei  being  arranged  at  such  heights  in  contiguous  cells 
as  not  to  interfere  with  each  other  by  mutual  pressure. 

4.  In  the  fourth  variety  of  epithelium  cells,  usually  cylin- 
drical, but  occasionally  of  some  other  shape,  are  provided  at 
their  free  extremities  with  several  fine  pellucid  pliant  processes 
or  cilia  (Figs.  6  and  7).  This  form  of  epithelium  lines  the 
whole  respiratory  tract  of  mucous  membrane  and  its  prolonga- 


EPITHELIUM. 


tions.  It  occurs  also  in  some  parts  of  the  generative  apparatus ; 
in  the  male,  lining  the  vasa  efferentia  of  the  testicle,  and  their 
prolongations  as  far  as  the  lower  end  of  the  epididymis;  and 


FIG.  6. 


FIG.  7. 


FIG.  6.  Spheroidal  ciliated  cells  from  the  mouth  of  the  frog ;  magnified  300  diameters 
(Sharpoy). 

FIG.  7.  Columnar  ciliated  epithelium  cells  from  the  human  nasal  membrane ; 
magnified  300  diameters  (Sharpey). 

in  the  female  commencing  about  the  middle  of  the  neck  of  the 
uterus,  and  extending  to  the  fimbriated  extremities  of  the 
Fallopian  tubes,  and  for  a  short  distance  along  the  peritoneal 
surface  of  the  latter.  A  tessellated  epithelium,  with  scales 
partly  covered  with  cilia,  lines,  in  great  part,  the  interior  of 
the  cerebral  ventricles,  and  of  the  minute  central  canal  of  the 
spinal  cord. 

If  a  portion  of  ciliary  mucous  membrane  from  a  living  or 
recently  dead  animal  be  moistened  and  examined  with  a  micro- 
scope, the  cilia  are  observed  to  be  in  constant  motion,  moving 
continually  backwards  and  forwards,  and  alternately  rising 
and  falling  with  a  lashing  or  fanning  movement.  The  ap- 
pearance is  not  unlike  that  of  the  waves  in  a  field  of  wheat, 
or  swiftly  running  and  rippling  water.  The  general  result  of 
their  movements  is  to  produce  a  continuous  current  in  a  de- 
terminate direction,  and  this  direction  is  invariably  the  same 
on  the  same  surface,  being  usually  in  the  case  of  a  cavity 
towards  its  external  orifice. 

Uses  of  Epithelium. — The  various  kinds  of  epithelium  serve 
one  general  purpose,  namely,  that  of  protecting,  and  at  the 
same  time  rendering  smooth,  the  surfaces  on  which  they  are 
placed.  But  each,  also,  discharges  a  special  office  in  relation 
to  the  particular  function  of  the  membrane  on  which  it  is 
placed. 

In  mucous  and  synovial  membranes  it  is  highly  probable 
that  the  epithelium  cells,  whatever  be  their  forms  and  what- 
ever their  other  functions,  are  the  organs  in  which  by  a  regular 
process  of  elaboration  and  secretion,  such  as  will  be  afterwards 


38 


ELEMENTARY    TISSUES. 


described,  mucus  and  synovial  fluid  are  formed  and  discharged. 
(See  chapter  on  Secretion.) 

Ciliated  epithelium  has  another  superadded  function.  By 
means  of  the  current  set  up  by  its  cilia  in  the  air  or  fluid  in 
contact  with  them,  it  is  enabled  to  propel  the  fluids  or  minute 
particles  of  solid  matter,  which  come  within  the  range  of  its 
influence,  and  aid  in  their  expulsion  from  the  body.  In  the 
respiratory  tract  of  mucous  membrane  the  current  set  up  in 
the  air  may  also  assist  in  the  diffusion  and  change  of  gases,  on 
which  the  due  aeration  of  the  blood  depends.  In  the  Fallopian 
tube  the  direction  of  the  current  excited  by  the  cilia  is  towards 
the  cavity  of  the  uterus,  and  may  thus  be  of  service  in  aiding 
the  progress  of  the  ovum.  Of  the  purposes  served  by  the  cilia 
which  line  the  ventricles  of  the  brain  nothing  is  known. 

The  nature  of  ciliary  motion  and  the  circumstances  by  which 
it  is  influenced  will  be  considered  hereafter.  (See  chapter  on 
Motion.) 

Epithelium  is  devoid  of  bloodvessels  and  lymphatics.  The 
cells  composing  it  are  nourished  by  absorption  of  nutrient 
matter  from  the  tissues  on  which  they  rest ;  and  as  they  grow 
old  they  are  cast  off  and  replaced  by  new  cells  from  beneath. 

Areolar,  Cellular,  or  Connective  Tissue. 

This  tissue,  which  has  received  various  names  according  to 
the  qualities  which  seemed  most  important  to  the  authors  who 

FIG.  8. 


Filaments  of  areolar  tissue,  in  larger  and  smaller  bundles,  as  seen  under  a  magni- 
fying power  of  400  diameters  (Sharpey). 


AREOLAR    TISSUE. 


39 


have  described  it,  is  met  with  in  some  form  or  other  in  every 
region  of  the  body;  the  areolar  tissue  of  one  district  being, 
directly  or  indirectly,  continuous  with  that  of  all  others.  In 
most  parts  of  the  body  this  structure  contains  fat,  but  the 
quantity  of  the  latter  is  very  variable,  and  in  some  few  re- 
gions it  is  absent  altogether  (p.  40).  Probably  no  nerves  are 
distributed  to  areolar  tissue  itself,  although  they  pass  through 
it  to  other  structures  ;  and  although  bloodvessels  are  supplied 
to  it,  yet  they  are  sparing  in  quantity,  if  we  except  those  des- 
tined for  the  fat  which  is  held  in  its  meshes. 

Under  the  microscope  areolar  tissue  seems  composed  of  a 
meshwork  of  fine  fibres  of  two  kinds.  The  first,  which  makes 
up  the  greater  part  of  the  tissue,  is  formed  of  very  fine  white 
structureless  fibres,  arranged  closely  in  bands  and  bundles,  of 
wavelike  appearance  when  not  stretched  out,  and  crossing 
and  intersecting  in  all  directions  (Fig,  8).  The  second  kind, 
or  the  yellow  elastic  fibre  (Fig,  10),  has  a  much  sharper  and 


FIG.  9. 


Magnified  view  of  areolar  tissues  (from  different  parts)  treated  with  acetic  acid. 
The  white  filaments  are  no  longer  seen,  and  the  yellow  or  elastic  fibres  with  the 
nuclei  come  into  view.  At  c,  elastic  fibres  wind  round  a  bundle  of  white  fibres, 
which,  by  the  effect  of  the  acid,  is  swollen  out  between  the  turns.  Some  connective- 
tissue  corpuscles  are  indistinctly  represented  in  c  (Sharpey). 

darker  outline,  and  is  not  arranged  in  bundles,  but  intimately 
mingled  with  the  first  variety,  as  more  or  less  separate  and 
well-defined  fibres,  which  twist  among  and  around  the  bundles 
of  white  filaments  (Fig.  9).  Sometimes  the  yellow  fibres 
divide  at  their  ends  and  anastomose  with  each  other  by 
means  of  the  branches.  Among  the  fibrous  parts  of  areolar 
or  connective-tissue  are  little  nuclear  bodies  of  various  shapes, 


40 


ELEMENTARY    TISSUES. 


FIG.  10. 


called  connective-tissue  corpuscles  (Fig.  9,  c),  some  of  which  are 
prolonged  at  various  points  of  their  outline  into  small  pro- 
cesses which  meet  and  join  others  like  them  proceeding  from 
their  neighbors. 

The  chief  functions  of  areolar  tissue  seem  to  consist  in  the 
investment  and  mechanical  support  of  various  parts,  and  as  a 

connecting  bond  between  such 
structures  as  may  need  it.  The 
connective-tissue  corpuscles, 
which,  according  to  Beale,  are 
small  branched  particles  of  ger- 
minal matter  or  protoplasm, 
probably  minister  to  the  nutri- 
tion of  the  texture  in  which  they 
are  seated. 

In  various  parts  of  the  body, 
each  of  the  two  constituents  of 
areolar  tissue  which  have  been 
just  mentioned,  may  exist  sepa- 
rately, or  nearly  so.  Thus  ten- 
dons, fasciae,  and  the  like  more 
or  less  inelastic  structures,  are 
formed  almost  exclusively  of 
the  white  fibrous  tissue,  arranged 


Elastic  fibres  from  the  ligamenta 
subflava,  magnified  about  200  diame- 
ters (Sharpey). 


according    to    the  purpose   re- 


quired, either  in  parallel  bun- 
dles or  membranous  meshes  ; 
while  the  yellow  elastic  fibres 
are  found  to  make  up  almost  alone  such  elastic  structures  as 
the  vocal  cords,  the  ligamenta  subflava,  &c.,  and  to  enter 
largely  into  the  composition  of  the  bloodvessels,  the  trachea, 
the  lungs,  and  many  other  parts  of  the  body. 


Adipose  Tissue. 

In  almost  all  regions  of  the  human  body  a  larger  or  smaller 
quantity  of  adipose  or  fatty  tissue  is  present ;  the  chief  excep- 
tions being  the  subcutaneous  tissue  of  the  eyelids,  penis  and 
scrotum,  the  nymphse,  and  the  cavity  of  the  cranium.  Adipose 
tissue  is  also  absent  from  the  substance  of  many  organs,  as  the 
lungs,  liver,  and  others. 

Fatty  matter,  not  in  the  form  of  a  distinct  tissue,  is  also 
widely  present  in  the  body,  as  the  fat  of  the  liver  and  brain, 
of  the  blood  and  chyle,  &c. 

Adipose  tissue  is  almost  always  found  seated  in  areolar 
tissue,  and  forms  in  its  meshes  little  masses  of  unequal  size 


AREOLAR    TISSUE. 


41 


and  irregular  shape,  to  which  the  term  lobules  is  commonly 
applied.  Under  the  microscope  it  is  found  to  consist  essentially 


FIG.  11. 


A  small  cluster  of  fat-cells ;  magnified  150  diameters  (Sharpey). 

of  little  vesicles  or  cells  about  ^J0tn  or  TOO^  °f  an  illcn  m 
diameter,  each  composed  of  a  structureless  and  colorless  mem- 
brane or  bag,  filled  with  fatty  matter,  which  is  liquid  during 
life,  but  in  part  solidified  after  death.  A  nucleus  is  always 
present  in  some  part  or  other  of  the  cell-wall ;  but  in  the  ordi- 
nary condition  of  the  cell  it  is  not  easily  or  always  visible. 
The  ultimate  cells  are  held  together  by  capillary  bloodvessels  ; 
while  the  little  clusters  thus  formed  are  grouped  into  small 
masses,  and  held  so,  in  most  cases,  by  areolar  tissue.  The  only 
matter  contained  in  the  cells  is  composed  chiefly  of  the  com- 
pounds of  fatty  acids  with  glycerin,  which  are  named  olein, 
stearin,  and  palmitin. 

It  is  doubtful  whether  lymphatics  or  nerves  are  supplied 
to  fat,  although  both  pass  through  it  on  their  way  to  other 
structures. 

Among  the  uses  of  fat,  these  seem  to  be  the  chief: 

1.  It  serves  as  a  store  of  combustible  matter  which  may  be 
reabsorbed  into  the  blood  when  occasion  requires,  and  being 
burnt,  may  help  to  preserve  the  heat  of  the  body. 

2.  That  part  of  the  fat  which  is  situate  beneath  the  skin 
must,  by  its  want  of  conducting  power,  assist  in  preventing 
undue  waste  of  the  heat  of  the  body  by  escape  from  the  sur- 
face. 

3.  As  a  packing  material,  fat  serves  very  admirably  to  fill 
up  spaces,  to  form  a  soft  and  yielding  yet  elastic  material 
wherewith  to  wrap  tender  and  delicate  structures,  or  form  a 
bed  with  like  qualities  on  which  such  structures  may  lie  unen- 
dangered  by  pressure.    As  good  examples  of  situations  in  which 


42  ELEMENTARY    TISSUES. 

fat  serves  such  purposes  may  be  mentioned  the  palms  of  the 
hands,  and  soles  of  the  feet,  and  the  orbits. 

4.  In  the  long  bones,  fatty  tissue,  in  the  form  known  as 
marrow,  serves  to  fill  up  the  medullary  canal,  and  to  support 
the  small  bloodvessels  which  are  distributed  from  it  to  the 
inner  part  of  the  substance  of  the  bone. 

Pigment. 

In  various  parts  of  the  body  there  exists  a  considerable 
quantity  of  dark  pigmentary  matter,  e.  g.,  in  the  choroid  coat 
of  the  eye,  at  the  back  of  the  iris,  in  the  skin,  &c.  In  all  these 
cases  the  dark  color  is  due  to  the  presence  of  so-called  pigment- 
cells. 

Pigment-cells  are  for  the  most  part  polyhedral  (Fig.  12)  or 
spheroidal,  although  sometimes  they  have  irregular  processes, 
as  shown  in  Fig.  13.  The  cell-wall  itself  is  colorless, — the 
dark  tint  being  produced  by  small  dark  granules  heaped  closely 
together,  and  more  or  less  concealing  the  nucleus,  itself  color- 

FIG.  12.  FIG.  1?. 


FIG.  12.  Pigment-cells  from  the  choroid;  magnified  370  diameters  (Henle).  A, 
cells  still  cohering,  seen  on  their  surface ;  6,  nucleus  indistinctly  seen.  In  the  other 
cells  the  nucleus  is  concealed  by  the  pigment-granules. 

FIG.  13.  Ramified  pigment-cells,  from  the  tissue  of  the  choroid  coat  of  the  eye  ; 
magnified  350  diameters  (after  Kolliker).  a,  cells  with  pigment ;  6,  colorless  fusi- 
form cells. 

less,  which  each  cell  contains.  The  dark  tint  of  the  skin,  in 
those  of  dark  complexion  and  in  the  colored  races,  is  seated 
chiefly  in  the  epidermis,  and  depends  on  the  presence  of  pig- 
ment-cells, which,  except  in  the  presence  of  the  dark  granules 
in  their  interior,  closely  resemble  the  colorless  cells  with  which 
they  are  mingled.  The  pigment-cells  are  situate  chiefly  in  the 


CARTILAGE.  43 

deep  layer  of  the  epidermis,  or  the  so-called  rete  mucosum.  (See 
chapter  on  the  Skin.) 

The  pigmentary  matter  is  a  very  insoluble  compound  of 
carbon,  hydrogen,  nitrogen,  and  oxygen,  —  the  carbon  largely 
predominating  ;  besides,  there  is  a  small  quantity  of  saline 
matter. 

The  uses  of  pigment  in  most  parts  of  the  body  are  not  clear. 
In  the  eyeball  it  is  evidently  intended  for  the  absorption  of 
superfluous  rays  of  light. 

Cartilage. 

Cartilage  or  gristle  exists  in  different  forms  in  the  human 
body,  and  has  been  classified  under  two  chief  heads,  namely, 
temporary  and  permanent  cartilage  ;  the  former  term  being  ap- 
plied to  that  kind  of  cartilage  which,  in  the  foetus  and  in 
young  subjects,  is  destined  to  be  converted  into  bone.  The 
varieties  of  permanent  cartilage  have  been  arranged  in  three 
classes,  namely,  the  cellular,  the  hyaline,  and  the  fibrous  carti- 
lages, —  the  last-named,  being  again  capable  of  subdivision  into 
two  kinds,  namely,  elastic  or  yellow  cartilage,  and  the  so-called 
fibro-cartilage. 

Elastic  cartilage,  however,  contains  fibres,  and  fibro-carti- 
lage is  more  or  less  elastic  ;  it  will  be  well,  therefore,  for  dis- 
tinction's sake  to  term  those  two  kinds  white  fibro-cartilage 
and  yellow  fibro-cartilage  respectively. 

The  accompanying  table  represents  the  classification  of  the 
varieties  of  cartilage  : 

1.  Temporary. 

f  A    Cellular. 

r  White  fibro-cartilage. 
C.  Fibrous.  fibro.cartilage. 


All  kinds  of  cartilage  are  composed  of  cells  imbedded  in  a 
substance  called  the  matrix  :  and  the  apparent  differences  of 
structure  met  with  in  the  various  kinds  of  cartilage  are  more 
due  to  differences  in  the  character  of  the  matrix  than  of  the 
cells.  Among  the  latter,  however,  there  is  also  considerable 
diversity  of  form  and  size. 

With  the  exception  of  the  articular  variety,  cartilage  is  in- 
vested by  a  thin  but  tough  and  firm  fibrous  membrane  called 
the  perichrondrium.  On  the  surface  of  the  articular  cartilage 
of  the  foetus,  the  perichondrium  is  represented  by  a  film  of 
epithelium  ;  but  this  is  gradually  worn  away  up  to  the  margin 
of  the  articular  surfaces,  when  by  use  the  parts  begin  to  suffer 
friction. 


44 


ELEMENTARY    TISSUES. 


FIG.  14. 


1.  Cellular  cartilage  may  be  readily  obtained  from  the  ex- 
ternal ear  of  rats,  mice,  or  other  small  mammals.  It  is  com- 
posed almost  entirely  of  cells  (hence  its  name),  with  little  or  no 
matrix.  The  latter,  when  present,  consists  of  very  fine  fibres, 
which  twine  about  the  cells  in  various  directions  and  inclose 

them  in  a  kind  of  network. 
The  cells  are  packed  very 
closely  together, — so  much  so 
that  it  is  not  easy  in  all  cases 
to  make  out  the  fine  fibres 
often  encircling  them. 

Cellular  cartilage  is  found 
in  the  human  subject,  only 
in  early  foetal  life,  when  it 
constitutes  the  Chorda  dorsalis. 
(See  chapter  on  Generation.) 
2.  Hyaline  cartilage  is  met 
with  largely  in  the  human 
body, — investing  the  articular 
ends  of  bones,  and  forming 
the  costal  cartilages,  the  nasal 
cartilages,  and  those  of  the 
larynx,  with  the  exception  of 
the  epiglottis  and  cornicula 
laryngis.  Like  other  carti- 
lages it  is  composed  of  cells 
imbedded  in  a  matrix  (Fig.  14). 
The  cells,  which  contain  a  nucleus  with  nucleoli,  are  irregu- 
lar in  shape,  and  generally  grouped  together  in  patches.  The 
patches  are  of  various  shapes  and  sizes,  and  placed  at  unequal 
distances  apart.  They  generally  appear  flattened  near  the  free 
surface  of  the  mass  of  cartilage  in  which  they  are  placed,  and 
more  or  less  perpendicular  to  the  surface  in  the  more  deeply 
seated  portions. 

The  matrix  in  which  they  are  imbedded  has  a  dimly  granu- 
lar appearance,  like  that  of  ground-glass. 

In  the  hyaline  cartilage  of  the  ribs,  the  cells  are  mostly 
larger  than  in  the  articular  variety,  and  there  is  a  tendency  to 
the  development  of  fibres  in  the  matrix.  The  costal  cartilages 
also  frequently  become  ossified  in  old  age,  as  also  do  some  of 
those  of  the  larynx. 

Temporary  cartilage  closely  resembles  the  ordinary  hyaline 
kind ;  the  cells,  however,  are  not  grouped  together  after  the 
fashion  just  described,  but  are  more  uniformly  distributed 
throughout  the  matrix. 

Articular  hyaline  cartilage  is  reckoned  among  the  so-called 


A  thin  layer  peeled  off  from  the  sur- 
face of  the  cartilage  of  the  head  of  the 
humerus,  showing  flattened  groups  of 
cells.  The  shrunken  cell-bodies  are  dis- 
tinctly seen,  but  the  limits  of  the  capsu- 
lar  cavities,  where  they  adjoin  one 
another,  are  but  faintly  indicated.  Mag- 
nified 400  diameters  (after  Sharpey). 


CARTILAGE.  45 

non-vascular  structures,  no  bloodvessels  being  supplied  directly 
to  its  own  substance;  it  is  nourished  by  those  of  the  bone  be- 
neath. When  hyaline  cartilage  is  in  thicker  masses,  as  in  the 
case  of  the  cartilages  of  the  ribs,  a  few  bloodvessels  traverse 
its  substance.  The  distinction,  however,  between  all  so-called 
vascular  and  non-vascular  parts,  is  at  the  best  a  very  artificial 
one.  (See  chapter  on  Nutrition.) 

Nerves  are  probably  not  supplied  to  any  variety  of  cartilage. 

Fibrous  cartilage,  as  before  mentioned,  occurs  under  two 
chief  forms,  the  yellow  and  the  white  fibre-cartilage. 

Yellow  fibro-cartilage  is  found  in  the  external  ear,  in  the 
epiglottis  and  cornicula  laryngis,  and  in  the  eyelid.  The  cells 
are  rounded  or  oval,  with  well-marked  nuclei  and  nucleoli. 
The  matrix  in  which  they  are  seated  is  composed  almost  en- 
tirely of  fine  fibres,  which  form  an  intricate  interlacement 
about  the  cells,  and  in  their  general  characters  are  allied  to 
the  yellow  variety  of  fibrous  tissue  (Fig.  15). 

White  fibro-cartilage,  which  is  much  more  widely  distributed 
throughout  the  body  than  the  foregoing  kind,  is  composed  like 
it,  of  cells  and  a  matrix ;  the 
latter,  however,  being  made  up  Fl°- 15- 

almost  entirely  of  fibres  close- 
ly resembling  those  of  white 
fibrous  tissue. 

In  this  kind  of  fibro-carti- 
lage it  is  not  unusual  to  find  a 
great  part  of  its  mass  composed 
almost  exclusively  of  fibres,  and 
deserving  the  name  of  cartilage 
only  from  the  fact  that  in 
another  portion,  continuous 
with  it,  cartilage-cells  may  be 

nrettv  freelv  distributed  Sectlou  of  the  e^loiiis'  magnified  380 

pretty  I    .Ciy  a  ea.  diameters  (Dr.  Baly). 

Ihe  different   situations   in 

which  white  fibro-cartilage  is  formed  have  given  rise  to  the 
following  classification : 

1.  Interarticular  fibro-cartilage,  e.  g.,  the  semilunar  carti- 
lages of  the  knee-joint. 

2.  Circumferential  or  marginal,  as  on  the  edges  of  the  ace- 
tabulum  and  glenoid  cavity  of  the  scapula. 

3.  Connecting,  e.  g.,  the  intervertebral  fibro-cartilages. 

4.  Fibro-cartilage  is  found  in  the  sheaths  of  tendons,  and 
sometimes  in  their  substance.     In   the   latter   situation,  the 
nodule  of  fibro-cartilage  is  called  a  sesamoid  fibro-cartilage,  of 
which  a  specimen  may  be  found  in  the  tenclon  of  the  tibialis 


46  ELEMENTARY    TISSUES. 

posticus,  iii  the  sole  of  the  foot,  and  usually  in  the  neighboring 
tendon  of  the  peroneus  longus. 

The  uses  of  cartilage  are  the  following :  in  the  joints,  to 
form  smooth  surfaces  ibr  easy  friction,  and  to  act  as  a  buffer, 
in  shocks ;  to  bind  bones  together,  yet  to  allow  a  certain  degree 
of  movement,  as  between  the  vertebrae ;  to  form  a  firm  frame- 
work and  protection,  yet  without  undue  stiffness  or  weight,  as 
in  the  larynx  and  chest-walls ;  to  deepen  joint-cavities,  as  in 
the  acetabulum,  yet  not  so  as  to  restrict  the  movements  of  the 
bones ;  to  be,  where  such  qualities  are  required,  firm,  tough, 
flexible,  elastic,  and  strong. 

Structure  of  Bones  and  Teeth. 

Bone  is  composed  of  earthy  and  animal  matter  in  the  pro- 
portion of  about  67  per  cent,  of  the  former  to  33  per  cent,  of 
the  latter.  The  earthy  matter  is  composed  chiefly  of  phos- 
phate of  lime,  but  besides  there  is  a  small  quantity,  about  11 
of  the  67  per  cent.,  of  carbonate  of  lime,  with  minute  quantities 
of  some  other  salts.  The  animal  matter  is  resolved  into  gela- 
tin by  boiling.  The  earthy  and  animal  constituents  of  bone 
are  so  intimately  blended  and  incorporated  the  one  with  the 
other,  that  it  is  only  by  chemical  action,  as,  for  instance,  by 
heat  in  one  case,  and  by  the  action  of  acids  in  another,  that 
they  can  be  separated.  Their  close  union,  too,  is  further 
shown  by  the  fact  that  when  by  acids  the  earthy  matter  is  dis- 
solved out,  or,  on  the  other  hand,  when  the  animal  part  is 
burnt  out,  the  general  shape  of  the  bone  is  alike  preserved. 

To  the  naked  eye  there  appear  two  kinds  of  structure  in 
different  bones,  and  in  different  parts  of  the  same  bone, 
namely,  the  dense  or  compact,  and  the  cancellous  tissue.  Thus, 
in  making  a  longitudinal  section  of  a  long  bone,  as  the  hume- 
rus  or  femur,  the  articular  extremities  are  found  capped  on 
their  surface  by  a  thin  shell  of  compact  bone,  while  their  in- 
terior is  made  up  of  the  spongy  or  cancellous  tissue.  The  shaft, 
on  the  other  hand,  is  formed  almost  entirely  of  a  thick  layer 
of  the  compact  bone,  and  this  surrounds  a  central  canal,  the 
medullary  cavity — so  called  from  its  containing  the  medulla  or 
marrow  (p.  42).  In  the  flat  bones,  as  the  parietal  bone  or  the 
scapula,  one  layer  of  the  cancellous  structure  lies  between  two 
layers  of  the  compact  tissue,  and  in  the  short  and  irregular 
bones,  as  those  of  the  carpus  and  tarsus,  the  cancellous  tissue 
alone  fills  the  interior,  while  a  thin  shell  of  compact  bone 
forms  the  outside.  The  spaces  in  the  cancellous  tissue  are 
filled  by  a  species  of  marrow,  which  differs  considerably  from 


B  O  N  E. 


47 


that  of  the  shaft  of  the  long  bones.     It  is  more  fluid,  and  of  a 
reddish  color,  and  contains  very  few  fat-cells. 

The  surfaces  of  bones,  except  the  parts  covered  with  articu- 
lar cartilage,  are  clothed  by  a  tough  fibrous  membrane,  the 
periosteum ;  and  it  is  from  the  bloodvessels  which  are  distrib- 
uted first  in  this  membrane,  that  the  bones,  especially  their 


FIG.  16. 


Transverse  section  of  compact  tissue  (of  humerus)  magnified  about  150  diameters. 
Three  of  the  Haversian  canals  are  seen,  with  their  concentric  rings;  also  the  cor- 
puscles or  lacunae,  with  the  canaliculi  extending  from  them  across  the  direction  of 
the  lamellae.  The  Haversian  apertures  had  got  filled  with  debris  in  grinding  down 
the  section,  and  therefore  appear  black  in  the  figure,  which  represents  the  object  as 
viewed  with  transmitted  light  (after  Sharpey). 

more  compact  tissue,  are  in  great  part  supplied  with  nourish- 
ment— minute  branches  from  the  peri  osteal  vessels  entering 
the  little  foramina  on  the  surface  of  the  bone,  and  finding 
their  way  to  the  Haversian  canals,  to  be  immediately  de- 
scribed. The  long  bones  are  supplied  also  by  a  proper  nutri- 
ent artery,  which,  entering  at  some  part  of  the  shaft  so  as  to 
reach  the  medullary  canal,  breaks  up  into  branches  for  the 
supply  of  the  marrow,  from  which  again  small  vessels  are  dis- 
tributed to  the  interior  of  the  bone.  Other  small  bloodvessels 
pierce  the  articular  extremities  for  the  supply  of  the  cancellous 
tissue. 

Notwithstanding  the  differences  of  arrangement  just  men- 


48  ELEMENTARY    TISSUES. 

tioned,  the  structure  of  all  bone  is  found,  under  the  microscope, 
to  be  essentially  the  same.  Examined  with  a  rather  high  power 
its  substance  is  found  occupied  by  a  multitude  of  little  spaces, 
called  lacunae,  with  very  minute  canals  or  canaliculi,  as  they 
are  termed,  leading  from  them,  and  anastomosing  with  similar 
little  prolongations  from  other  lacunae  (Fig.  16).  In  very  thin 
layers  of  bone,  no  other  canals  than  these  may  be  visible ;  but 
on  making  a  transverse  section  of  the  compact  tissue,  e.  g.,  of 
a  long  bone,  as  the  humerus  or  ulna,  the  arrangement  shown 
in  Fig.  16  can  be  seen.  The  bone  seems  mapped  out  into  small 
circular  districts,  at  or  about  the  centre  of  each  of  which  is  a 
hole,  and  around  this  an  appearance  as  of  concentric  layers  ; 
the  lacunce  and  canaliculi  following  the  same  concentric  plan 
of  distribution  around  the  small  hole  in  the  centre,  with 
which,  indeed,  they  communicate.  On  making  a  longitudinal 
section,  the  central  holes  are  found  to  be  simply  the  cut  ex- 
tremities of  small  canals  which  run  lengthwise  through  the 
bone  (Fig.  17),  and  are  called  Haversian  canals,  after  the 
name  of  the  physician,  Cloptou  Havers,  who  first  accurately 
described  them. 

The  Haversian  canals,  the  average  diameter  of  which  is 
of  an  inch,  contain  bloodvessels,  and  by  means  of  them  blo 
is  conveyed  to  all,  even  the  densest  parts  of  the  bone ;  the  mi- 
nute canaliculi  and  lacunae  absorbing  nutrient  matter  from  the 
Haversian  bloodvessels,  and  conveying  it  still  more  intimately 
to  the  very  substance  of  the  bone  which  they  traverse.  The 
bloodvessels  enter  the  Haversian  canals  both  from  without,  by 
traversing  the  small  holes  which  exist  on  the  surface  of  all 
bones  beneath  the  periosteum,  and  from  within  by  means  of 
small  channels  which  extend  from  the  medullary  cavity,  or 
from  the  cancellous  tissue.  According  to  Todd  and  Bowman, 
the  arteries  and  veins  usually  occupy  separate  canals,  and  the 
veins,  which  are  the  larger,  often  present,  at  irregular  intervals, 
small  pouch-like  dilatations  (Fig.  17). 

The  lacunce  are  occupied  by  nucleated  cells,  or,  as  Dr.  Beale 
expresses  it,  minute  portions  of  protoplasm  or  germinal  matter; 
and  there  is  every  reason  to  believe  that  the  lacunar  cells  are 
homologous  with  the  corpuscles  of  the  connective  tissue,  each 
little  particle  of  protoplasm  ministering  to  the  nutrition  of  the 
bone  immediately  surrounding  it,  and  one  lacunar  particle 
communicating  with  another,  and  with  its  surrounding  district, 
and  with  the  bloodvessels  of  the  Haversian  canals,  by  means 
of  the  minute  streams  of  fluid  nutrient  matter  which  occupy 
the  canaliculi. 

Besides  the  concentric  lamellce  of  bone-tissue  which  surround 
the  Haversian  canal  in  the  shaft  of  a  long  bone,  are  others,  es- 


BONE. 


49 


pecially  near  the  circumference,  which  surround  the  whole 
bone,  and  are  arranged  concentrically  with  regard  to  the 
medullary  canal. 

The  ultimate  structure  of  the  lamellae  appears  to  be  reticular. 
If  a  thin  film  be  peeled  off  the  surface  of  a  bone  from  which 


FIG.  17. 


FIG.  18. 


FIG.  17.  Haversian  canals,  seen  in  a  longitudinal  section  of  the  compact  tissue  of 
the  shaft  of  one  of  the  long  bones.  1.  Arterial  canal ;  2.  Venous  canal ;  3.  Dilatation 
of  another  venous  canal. 

FIG.  18.  Thin  layer  peeled  off  from  a  softened  bone,  as  it  appears  under  a  magni- 
fying power  of  400.  This  figure,  which  is  intended  to  represent  the  reticular  struc- 
ture of  a  lamella,  gives  a  better  idea  of  the  object  when  held  rather  farther  off  than 
usual  from  the  eye  (from  Sharpey). 

the  earthy  matter  has  been  removed  by  acid,  and  examined 
with  a  high  power  of  the  microscope,  it  will  be  found  composed, 
according  to  Sharpey,  of  a  finely  reticular  structure,  formed 
apparently  of  very  slender  fibres  decussating  obliquely,  but 
coalescing  at  the  points  of  intersection,  as  if  here  the  fibres  were 
fused  rather  than  woven  together  (Fig.  18). 

In  many  places  these  reticular  lamellae  are  perforated  by 
tapering  fibres,  resembling  in  character  the  ordinary  white  or 
rarely  the  elastic  fibrous  tissue,  which  bolt  the  neighboring 
lamellae  together,  and  may  be  drawn  out  when  the  latter  are 
torn  asunder  (Fig.  19). 

Bone  is  developed  after  two  different  fashions.     In  one,  the 


50 


ELEMENTARY    TISSUES. 


tissue  in  which  the  earthy  matter  is  laid  down  is  a  membrane, 
composed  mainly  of  fibres  and  granular  cells,  like  imperfectly 
developed  connective-tissues.  Of  this  kind  of  ossification  in 
membrane,  the  flat  bones  of  the  skull  are  examples.  In  the 
other,  and  much  more  common  case,  of  which  a  long  bone  may 
be  cited  as  an  instance,  the  ossification  takes  place  in  car- 
tilage. 

In  most  bones  ossification  begins  at  more  than  one  point ; 
and  from  these  centres  of  ossification,  as  they  are  called,  the 
process  of  deposition  of  calcareous  matter  advances  in  all 
directions.  Bones  grow  by  constant  development  of  the  car- 
tilage or  membrane  between  these  centres  of  ossification,  until 
by  the  process  of  calcification  advancing  at  a  quicker  rate  than 
the  development  of  the  softer  structures,  the  bone  becomes  im- 


FlG.  19. 


Lamellae  torn  off  from  a  decalcified  human  parietal  bone  at  some  depth  from  the 
surface,  a,  a  lamella,  showing  reticular  fibres ;  ft,  b,  darker  part,  where  several 
lamellae  are  superposed  ;  c,  c,  perforating  fibres.  Apertures  through  which  perfor- 
ating fibres  had  passed,  are  seen  especially  ill  the  lower  part,  a,  a,  of  the  figure. 
Magnitude  as  seen  under  a  power  of  200,  but  not  drawn  to  a  scale  (from  a  drawing 
by  Dr.  Allen  Thomson). 

pregnated  throughout  with  calcareous  matter,  and  can  grow 
no  more.  In  the  long  bones  the  main  centres  of  ossification 
are  seated  at  the  middle  of  the  shaft,  and  at  each  of  the  ex- 
tremities. Increase  of  the  length  of  bones,  therefore,  occurs  at 


TEETH.  51 

the  part  which  intervenes  between  the  ossifying  centre  in  the 
shaft  and  that  at  each  extremity ;  while  increase  in  thickness 
takes  place  by  the  formation  of  layers  of  osseous  tissue  beneath 
the  periosteum.  The  former  is  an  example  of  ossification  in 
cartilage ;  the  latter  of  ossification  in  membrane. 

Teeth. — A  tooth  is  generally  described  as  possessing  a  crown, 
neck,  and  fang  or  fangs.  The  crown  is  the  portion  which  pro- 
jects beyond  the  level  of  the  gum.  The  neck  is  that  constricted 
portion  just  below  the  crown,  which  is  embraced  by  the  free 
edges  of  the  gum,  and  the  fang  includes  all  below  this. 

On  making  a  longitudinal  section  through  the  centre  of  a 
tooth  (Figs.  20  and  21),  it  is  found  to  be  principally  composed 
of  a  hard  matter,  dentine  or  ivory ;  while  in  the  centre  this 
dentine  is  hollowed  out  into  a  cavity  resembling  in  general 
shape  the  outline  of  the  tooth,  and  called  the  pulp-cavity,  from 
its  containing  a  very  vascular  and  sensitive  little  mass  com- 
posed of  connective  tissue,  bloodvessels  and  nerves,  which  is 
called  the  tooth-pulp.  The  pulp  is  continuous  below,  through 
an  opening  at  the  end  of  the  fang,  with  the  mucous  membrane 
of  the  gum.  Capping  that  part  of  the  dentine  which  projects 


FIG.  20. 


Sections  of  an  Incisor  and  Molar  Tooth.— The  longitudinal  sections  show  the  whole 
of  the  pulp-cavity  in  the  incisor  and  molar  teeth,  its  extension  upwards  within  the 
crown,  and  its  prolongation  downwards  into  the  fangs,  with  the  small  aperture  at 
the  point  of  each;  these  and  the  cross-section  show  the  relation  of  the  dentine  and 
enamel. 

beyond  the  level  of  the  gum,  is  a  layer  of  very  hard  calcareous 
matter,  the  enamel,  while  sheathing  the  portion  of  dentine  which 
is  beneath  the  level  of  the  gum,  is  a  layer  of  true  bone,  called  the 
cement  or  crusta  petrosa.  At  the  neck  of  the  tooth  the  cement 
is  exceedingly  thin,  but  it  gradually  becomes  thicker  as  it  ap- 
proaches and  covers  the  lower  end  or  apex  of  the  fang. 

Dentine  or  ivory  in  chemical  composition  closely  resembles 


52 


ELEMENTARY    TISSUES. 


FIG.  21. 


bone.  It  contains,  however,  rather  less  animal  matter ;  the 

proportion  in  100  parts  being 
about  28  of  animal  matter  to 
72  of  earthy.  The  former,  like 
the  animal  matter  of  bone,  may 
be  resolved  into  gelatin  by  boil- 
ing. The  earthy  matter  is  made 
up  chiefly  of  phosphate  of  lime, 
with  a  small  portion  of  the  car- 
bonate, and  traces  of  some  other 
salts. 

Under  the  microscope,  den- 
tine is  seen  to  be  finely  chan- 
nelled by  a  multitude  of  fine 
tubes,  which,  by  their  inner 
ends,  communicate  with  the 
pulp-cavity,  and  by  their  outer 
extremities  come  into  contact 
with  the  under  part  of  the  en- 
amel and  cement,  and  some- 
times even  penetrate  them  for 
a  greater  or  less  distance.  In 
their  course  from  the  pulp-cavity 
to  the  surface  of  the  dentine, 
these  minute  tubes  form  gentle 
and  nearly  parallel  curves,  and 
divide  and  subdivide  dichotom- 
ously,  but  without  much  lessen- 
ing of  their  calibre  until  they 
are  approaching  their  peripheral 
termination.  From  their  sides 
proceed  other  exceedingly  mi- 
nute secondary  canals,  which 
extend  into  the  dentine  between 
the  tubules. 

The  tubules  of  the  dentine, 


Magnified  Longitudinal  Section  of  a 
Bicuspid  Tooth  (after  Retzius)— 1,  the 
ivory  or  dentine,  showing  the  direc- 
tion and  primary  curves  of  the  dental 
tubuli;  2,  the  pulp-cavity,  with  the 
small  apertures  of  the  tubuli  into  it; 
3,  the  cement  or  crusta  petrosa,  cover- 
ing the  fang  as  high  as  the  border  of 
the  enamel  at  the  neck,  exhibiting 

lacuna? ;  4,  the  enamel  resting  on  the       ,  •,  f 

dentine;  this  has  been  worn  away  by      the  average    diameter   of  which 

use  from  the  upper  part.  at  their  inner  and  larger  ex- 

tremity is  4^0  o  °f  an  incn>  con" 

tain  fine  prolongations  from  the  tooth-pulp,  which  give  the  den- 
tine a  certain  faint  sensitiveness  under  ordinary  circumstances, 
and  without  doubt,  have  to  do  also  with  its  nutrition. 

The  enamel,  which  is  by  far  the  hardest  portion  of  a  tooth, 
is  composed,  chemically,  of  the  same  elements  that  enter  into 
the  composition  of  dentine  and  bone.  Its  animal  matter,  how- 
ever, amounts  only  to  about  2  or  3  per  cent. 


TEETH. 


53 


FIG.  22. 


Examined  under  the  microscope,  enamel  is  found  composed 
of  fine  hexagonal  fibres  (Figs.  22  and 
23),  which  are  set  on  end  on  the  sur- 
face of  the  dentine,  and  fit  into  cor- 
responding depressions  in  the  same. 
They  radiate  in  such  a  manner  from 
the  dentine  that  at  the  top  of  the 
tooth  they  are  more  or  less  vertical, 
while  towards  the  sides  they  tend  to 
the  horizontal  direction.  Like  the 
dentine-tubules,  they  are  not  straight, 
but  disposed  in  wavy  and  parallel 
curves.  The  fibres  are  marked  by 
transverse  lines,  and  are  mostly  solid, 
but  some  of  them  contain  a  very 
minute  canal. 

The  enamel  itself  is  coated  on  the 
outside  by  a  very  thin  calcified  mem- 
brane, sometimes  termed  the  cuticle  of 
the  enamel. 

The  crusta  petrosa,  or  cement,  is 
composed  of  true  bone,  and  in  it  are 
lacunae  and  canaliculi  which  some- 
times communicate  with  the  outer 
finely-branched  ends  of  the  dentine- 
tubules. 

Development  of  Teeth. — The  teeth 
are  developed  after  the  following 
manner :  Along  the  free  edge  of  the 
toothless  gum  in  the  foetus,  there  ex- 
tends a  groove,  or  small  trench,  the 
primitive  dental  groove  (Goodsir),  and 
from  the  bottom  of  this  project  ten 
small  processes  of  mucous  membrane, 
or  papillae,  containing  bloodvessels  and 
nerves.  As  these papillce  grow  up  from 
below,  the  edges  of  the  small  trench 
begin  to  grow  in  towards  each  other, 

and  overshadow  them,  at  the  same  time  that  each  papilla  is 
cut  off  from  its  neighbor  by  the  extension  of  a  partition  wall 
from  the  gum,  which  grows  in  from  each  side  to  separate  the 
one  from  the  other.  Thus  closed  in  above  and  all  around, 
each  dental  papilla  is  at  length  contained  in  a  separate  sac, 
and  gradually  assumes  the  character  of  a  tooth  by  deposition 
on  its  surface  of  the  various  hard  matters  which  have  been 
just  enumerated  as  composing  the  greater  part  of  a  tooth's 


7) 


Thin  section  of  the  enamel 
and  a  part  of  the  dentine 
(from  Kolliker)  &%&.  a,  cu- 
ticular  pellicle  of  the  enamel ; 
b,  enamel  fibres,  or  columns 
with  fissures  between  them 
and  cross  striae ;  c,  larger  cavi- 
ties in  the  enamel,  communi- 
cating with  the  extremities 
of  some  of  the  tubuli  (d). 


54 


ELEMENTARY    TISSUES. 


substance.  The  small  vascular  papilla  is  gradually  encroached 
upon  and  imprisoned  by  the  calcareous  deposit,  until  only  a 
small  part  of  it  is  left  as  the  tooth-pulp,  which  remains  shut  up 
in  the  harder  substance,  with  only  the  before-mentioned  small 


FIG.  23. 


Enamel  fibres  (from  Kolliker)  ^f fi.  A,  fragments  and  single  fibres  of  the  enamel, 
isolated  by  the  action  of  hydrochloric  acid.  B,  surface  of  a  small  fragment  of  enamel, 
showing  the  hexagonal  ends  of  the  fibres. 

communication  with  the  outside,  through  the  end  of  the  fang. 
In  this  manner  the  first  set  of  teeth,  or  the  milk  teeth,  are 
formed ;  and  each  tooth,  by  degrees  developing,  presses  at 
length  on  the  wall  of  the  sac  inclosing  it,  and  causing  its  ab- 
sorption, is  cut,  to  use  a  familiar  phrase. 

The  temporary  or  milk  teeth,  having  only  a  very  limited  term 
of  existence,  gradually  decay  and  are  shed,  while  the  per- 
manent teeth  push  their  way  from  beneath,  by  gradual  increase 
and  development,  so  as  tb  succeed  them. 

The  temporary  teeth  are  ten  in  each  jaw,  namely,  four  in- 
cisors, two  canines,  and  four  molars,  and  are  replaced  by  ten 
permanent  teeth,  each  of  which  is  developed  from  a  small  sac 
set  by,  so  to  speak,  from  the  sac  of  the  temporary  tooth 
which  precedes  it  and  called  the  cavity  of  reserve.  The  num- 
ber of  the  permanent  teeth  is,  however,  increased  to  sixteen, 
by  the  development  of  three  others  on  each  side  of  the  jaw 
after  much  the  same  fashion  as  that  by  which  the  milk  teeth 
were  themselves  formed.  The  beginning  of  the  development 


THE    BLOOD.  55 

of  the  permanent  teeth  of  course  takes  place  long  before  the 
cutting  of  those  which  they  are  to  succeed;  one  of  the  first 
acts  of  the  newly-formed  little  dental  sac  of  a  milk-tooth  being 
to  set  aside  a  portion  of  itself  as  the  germ  of  its  successor. 

The  following  formula  shows,  at  a  glance,  the  comparative 
arrangement  and  number  of  the  temporary  and  permanent 
teeth : 

MO.  CA.  IN.  CA.  MO. 

f  Upper,      21412  =10 

Temporary  Teeth,.     .      \  =20 

(Lower,    ^21412  =10 

MO.  BI.    CA.  IN.    CA.  BI.   MO. 

(Upper,      321412     3  =  16 

Permanent  Teeth,.     .      \  -  — =32 

(Lower,      3     2     1     4     1     2    3  =  16 

From  this  formula  it  will  be  seen  that  the  two  bicuspid  teeth 
in  the  adult  are  the  successors  of  the  two  molars  in  the  child. 
They  differ  from  them,  however,  in  some  respects,  the  tem- 
porary molars  having  a  stronger  likeness  to  the  permanent 
than  to  their  immediate  descendants,  the  so-called  bicuspids. 
The  temporary  incisors  and  canines  differ  but  little,  except  in 
their  smaller  size,  from  their  successors. 


CHAPTER  V. 

THE   BLOOD. 

ALTHOUGH  it  may  seem,  in  some  respects,  un advisable  to 
describe  the  blood  before  entering  upon  the  physiology  of  those 
subservient  processes  which  have  for  their  end  or  purpose  its 
formation  and  development,  yet  there  are  many  reasons  for 
taking  such  a  course,  and  we  may  therefore  at  once  proceed 
to  consider  the  structural  and  chemical  composition  of  this 
fluid. 

Wherever  blood  can  be  seen  under  a  moderately  high  micro- 
scopic power  as  it  flows  in  the  vessels  of  a  living  part,  it  appears 
a  colorless  fluid  containing  minute  colored  particles.  The 
greater  part  of  these  particles  are  red,  when  seen  en  masse, 
and  they  are  the  source  of  the  color  which,  so  far  as  the  naked 
eye  can  see,  belongs  to  every  part  of  the  blood  alike.  The 
colorless  fluid  is  named  liquor  sanguinis ;  the  particles  are  the 


56  THE    BLOOD. 

blood-corpuscles  or  blood-cells.     The  structural  composition  of 
the  blood  may  be  thus  expressed : 

f  Corpuscles,  .  .  1  Clot  (containing  also 

T-  ,-j  pi^«,i  f  more  or  less  serum). 

Liquid  Mood,  j  LiqnorSanguinisC  Fibrin,  \ 

[      or  Plasma.          \Serum. 

When  blood  flows  from  the  living  body,  it  is  a  thickish 
heavy  fluid,  of  a  bright  scarlet  color  when  it  comes  from  an 
artery;  deep  purple,  or  nearly  black,  when  it  flows  from  a 
vein.  Its  specific  gravity  at  60°  F.  is,  on  an  average,  1055, 
that  of  water  being  reckoned  as  1000 ;  the  extremes  consistent 
with  health  being  1050  and  1059.  Its  temperature  is  generally 
about  100°  F.;  but  it  is  not  the  same  in  all  parts  of  the  body. 
Thus,  while  the  stream  is  slightly  warmed  by  passing  through 
the  liver  and  some  other  parts,  it  is  slightly  cooled,  according 
to  Bernard,  by  traversing  the  capillaries  of  the  skin.  The 
temperature  of  blood  in  the  left  side  of  the  heart  is,  again  1° 
or  2°  higher  than  in  the  right  (Savory). 

The  blood  has  a  slight  alkaline  reaction ;  and  emits  an  odor 
similar  to  that  which  issues  from  the  skin  or  breath  of  the 
animal  from  which  it  flows,  but  fainter.  The  alkaline  reac- 
tion appears  to  be  a  constant  character  of  blood  in  all  animals 
and  under  all  circumstances.  An  exception  has  been  supposed 
to  exist  in  the  case  of  menstrual  blood  ;  but  the  acid  reaction 
which  this  sometimes  presents  is  due  to  the  mixture  of  an  acid 
mucus  from  the  uterus  and  vagina.  Pure  menstrual  blood, 
such  as  may  be  obtained  with  a  speculum,  or  from  the  uteri 
of  women  who  die  during  menstruation,  is  always  alkaline, 
and  resembles  ordinary  blood.  According  to  Bernard,  blood 
becomes  spontaneously  acid  after  removal  from  the  body, 
owing  to  conversion  of  its  sugar  into  lactic  acid. 

The  odor  of  blood  is  easily  perceived  in  the  watery  vapor, 
or  halitus  as  it  is  called,  which  rises  from  blood  just  drawn  :  it 
may  also  be  set  free,  long  afterwards,  by  adding  to  the  blood 
a  mixture  of  equal  parts  of  sulphuric  acid  and  water.  It  is 
said  to  be  not  difficult  to  tell,  by  the  likeness  of  the  odor  to 
that  of  the  body,  the  species  of  domestic  animal  from  which 
any  specimen  of  blood  has  been  taken  :  the  strong  odor  of  the 
pig  or  cat,  and  the  peculiar  milky  smell  of  the  cow,  are  es- 
pecially easy  to  be  thus  discerned  in  their  blood  (Barruel). 

Quantity  of  Blood. 

Only  an  imperfect  indication  of  the  whole  quantity  of  blood 
in  the  body  is  afforded  by  measurement  of  that  which  escapes, 
when  an  animal  is  rapidly  bled  to  death,  inasmuch  as  a  cer- 


QUANTITY    OF    BLOOD.  57 

tain  amount  always  remains  in  the  bloodvessels.  In  cases  of 
less  rapid  bleeding,  on  the  other  hand,  when  life  is  more  pro- 
longed, and  when,  therefore,  sufficient  time  elapses  before 
death  to  allow  some  absorption  into  the  circulating  current  of 
the  fluids  of  the  body  (p.  76),  the  whole  quantity  of  blood  that 
escapes  may  be  greater  than  the  whole  average  amount  natur- 
ally present  in  the  vessels. 

Various  means  have  been  devised,  therefore,  for  obtaining 
a  more  accurate  estimate  than  that  which  results  from  merely 
bleeding  animals  to  death. 

Welcker's  method  is  the  following.  An  animal  is  rapidly 
bled  to  death,  and  the  blood  which  escapes  is  collected  and 
measured.  The  blood  remaining  in  the  smaller  vessels  is  then 
removed  by  the  injection  of  water  through  them,  and  the  mix- 
ture of  blood  and  water  thus  obtained,  is  also  collected.  The 
animal  is  then  finely  minced,  and  infused  in  water,  and  the 
infusion  is  mixed  with  the  combined  blood  and  water  pre- 
viously obtained.  Some  of  this  fluid  is  then  brushed  on  a 
white  ground,  and  the  color  compared  with  that  of  mixtures 
of  blood  and  water  whose  proportions  have  been  previously 
determined  by  measurement.  In  this  way  the  materials  are 
obtained  for  a  fairly  exact  estimate  of  the  quantity  of  blood 
actually  existing  in  the  body  of  the  animal  experimented  on. 

Another  method  (that  of  Vierordt)  consists  in  estimating 
the  amount  of  blood  expelled  from  the  ventricle,  at  each  beat 
of  the  heart,  and  multiplying  this  quantity  by  the  number  of 
beats  necessary  for  completing  the  "round"  of  the  circulation. 
This  method  is  ingenious,  but  open  to  various  objections,  the 
most  conclusive  being  the  uncertainty  of  all  the  premises  on 
which  the  conclusion  is  founded. 

Other  methods  depend  on  the  results  of  injecting  a  known 
quantity  of  water  (Valentin)  or  of  saline  matters  (Blake)  into 
the  bloodvessels ;  the  calculation  being  founded  in  the  first  case, 
on  the  diminution  of  the  specific  gravity  which  ensues,  and 
in  the  other,  on  the  quantity  of  the  salt  found  diffused  in  a  cer- 
tain measured  amount  of  the  blood  abstracted  for  experiment. 

A  nearly  correct  estimate  was  probably  made  by  Weber 
and  Lehmann,  from  the  following  data.  A  criminal  was 
weighed  before  and  after  decapitation ;  the  difference  in  the 
weight  representing,  of  course,  the  quantity  of  blood  which 
escaped.  The  bloodvessels  of  the  head  and  trunk,  were  then 
washed  out  by  the  injection  of  water,  until  the  fluid  which 
escaped  had  only  a  pale  red  or  straw  color.  This  fluid  was 
then  also  weighed ;  and  the  amount  of  blood  which  it  repre- 
sented was  calculated,  by  comparing  the  proportion  of  solid 
matter  contained  in  it,  with  that  of  the  first  blood  which 


58  THE     BLOOD. 

escaped  on  decapitation.  Two  experiments  of  this  kind  gave 
precisely  similar  results. 

The  most  reliable  of  these  various  means  for  estimating  the 
quantity  of  blood  in  the  body  yield  as  nearly  similar  results 
as  can  be  expected,  when  the  sources  of  error  unavoidably 
present  in  all,  are  taken  into  consideration;  and  it  may  be 
stated  that  in  man,  the  weight  of  the  whole  quantity  of  blood, 
compared  with  that  of  the  body,  is  from  about  1  to  8,  to  1  to  10. 

It  must  be  remembered,  however,  that  the  whole  quantity 
of  blood  varies,  even  in  the  same  animal,  very  considerably, 
in  correspondence  with  the  different  amounts  of  food  and  drink, 
which  may  have  been  recently  taken  in,  and  the  equally  vary- 
ing quantity  of  matter  given  out.  Bernard  found  by  experi- 
ment, that  the  quantity  of  blood  obtainable  from  a  fasting 
animal  is  scarcely  more  than  half  of  that  which  is  present 
soon  after  a  full  meal.  The  estimate  above  given,  must  there- 
fore be  taken  to  represent  only  an  approximate  average. 

Coagulation  of  the  Blood. 

When  blood  is  drawn  from  the  body,  and  left  at  rest,  cer- 
tain changes  ensue,  which  constitute  a  kind  of  rough  analysis 
of  it,  and  are  instructive  respecting  the  nature  of  some  of  its 
constitutents.  After  about  ten  minutes,  taking  a  general 
average  of  many  observations,  it  gradually  clots  or  coagulates, 
becoming  solid  like  a  soft  jelly.  The  clot  thus  formed  has  at 
first  the  same  volume  and  appearance  as  the  fluid  blood  had, 
and,  like  it,  looks  quite  uniform ;  the  only  change  seems  to  be, 
that  the  blood  which  was  fluid  is  now  solid.  But  presently, 
drops  of  transparent  yellowish  fluid  begin  to  ooze  from  the 
surface  of  the  solid  clot;  and  these  gradually  collecting,  first 
on  its  upper  surface,  and  then  all  around  it,  the  clot  or  "  cras- 
samentum"  diminished  in  size,  but  firmer  than  it  was  before, 
floats  in  a  quantity  of  yellowish  fluid,  which  is  named  serum, 
the  quantity  of  which  may  continually  increase  for  from  twenty- 
four  to  forty-eight  hours  after  the  clotting  of  the  blood. 

The  changes  just  described  may  be  thus  explained.  The 
liquor  sanguinis,  or  liquid  part  of  the  blood  (p.  55),  consists  of 
a  thin  fluid  called  serum,  holding  fibrin  in  solution.1  The 
peculiar  property  of  fibrin,  as  already  said,  is  its  tendency  to 
become  solid  when  at  rest,  and  in  some  other  conditions.  When, 
therefore,  a  quantity  of  blood  is  drawn  from  the  vessels,  the 
fibrin  coagulates,  and  the  blood-corpuscles,  with  part  of  the 

1  This  statement  has  been  left  unaltered  in  the  text ;  but,  as  will 
be  seen  farther  on,  it  requires  modification. — (ED.) 


COAGULATION    OF    BLOOD.  59 

serum,  are  held,  or,  as  it  were,  entangled  in  the  solid  substance 
which  it  forms. 

But  after  healthy  fibrin  has  thus  coagulated,  it  always  con- 
tracts ;  and  what  is  generally  described  as  one  process  of  coagu- 
lation should  rather  be  regarded  as  consisting  of  two  parts  or 
stages  ;  namely,  first,  the  simple  act  of  clotting,  coagulating,  or 
becoming  solid ;  and,  secondly,  the  contraction  or  condensa- 
tion of  the  solid  clot  thus  formed.  By  this  second  act  much 
of  the  serum  which  was  soaked  in  the  clot  is  gradually  pressed 
out ;  and  this  collects  in  the  vessel  around  the  contracted  clot. 

Thus,  by  the  observation  of  blood  within  the  vessels,  and  of 
the  changes  which  commonly  ensue  when  it  is  drawn  from  them, 
we  may  distinguish  in  it  three  principal  constituents,  namely, 
1st,  the  fibrin,  or  coagulating  substance ;  2d,  the  serum ;  3d, 
the  corpuscles. 

That  the  fibrin  is  the  only  spontaneously  coagulable  material 
in  the  blood,  may  be  proved  in  many  ways ;  and  most  simply 
by  employing  any  means  whereby  a  portion  of  the  liquor  san- 
guinis,  i.  e.,  the  serum  and  fibrin,  can  be  separated  from  the 
red  corpuscles  before  coagulation.  Under  ordinary  circum- 
stances coagulation  occurs  before  the  red  corpuscles  have  had 
time  to  subside ;  and  thus,  from  their  being  entangled  in  the 
meshes  of  the  fibrin,  the  clot  is  of  a  deep  dark  red  color  through- 
out,— somewhat  darker,  it  may  be,  at  the  most  dependent  part, 
from  accumulation  of  red  cells,  but  not  to  any  very  marked 
degree.  If,  however,  from  any  cause,  the  red  cells  sink  more 
quickly  than  usual,  or  the  fibrin  contracts  more  slowly,  then, 
in  either  of  these  cases,  the  red  corpuscles  may  be  observed, 
while  the  blood  is  yet  fluid,  to  sink  below  its  surface ;  and  the 
layer  beneath  which  they  have  sunk,  and  which  has  usually  an 
opaline  or  grayish-white  tint,  will  coagulate  without  them,  and 
form  a  white  clot  consisting  of  fibrin  alone,  or  of  fibrin  with 
entangled  white  corpuscles;  for  the  white  corpuscles,  being 
very  light,  tend  upwards  towards  the  surface  of  the  fluid.  The 
layer  of  white  clot  which  is  thus  formed  rests  on  the  top  of  a 
colored  clot  of  ordinary  character,  i.  e.,  of  one  in  which  the 
coagulating  fibrin  has  entangled  the  red  corpuscles  while  they 
were  sinking :  and,  thus  placed,  it  constitutes  what  has  been 
called  a  buffy  coat. 

When  a  buffy  coat  is  formed  in  the  manner  just  described, 
it  commonly  contracts  more  than  the  rest  of  the  clot  does,  and, 
drawing  in  at  its  sides,  produces  a  cupped  appearance  on  the 
top  of  the  clot. 

In  certain  conditions  of  the  system,  and  especially  when  there 
exists  some  local  inflammation,  this  buffed  and  cupped  con- 
dition of  the  clot  is  well  marked,  and  there  has  been  much  dis- 


60  THE    BLOOD. 

cussion  concerning  its  origin  under  these  circumstances.  It  is 
now  generally  agreed  that  two  causes  combine  to  produce  it. 

In  the  first  place,  the  tendency  of  the  red  corpuscles  to  form 
rouleaux  (see  p.  68)  is  much  exaggerated  in  inflammatory 
blood ;  and  as  their  rate  of  sinking  increases  with  their  aggre- 
gation, there  is  a  ready  explanation,  at  least  in  part,  of  the 
colorless  condition  of  the  top  of  the  clot.  And  in  the  next 
place,  inflammatory  blood  coagulates  less  rapidly  than  usual, 
and  thus  there  is  more  time  for  the  already  rapidly  sinking 
corpuscles  to  subside.  The  colorless  or  buffed  condition  of  the 
upper  part  of  the  clot  is  therefore,  readily  accounted  for;  while 
the  cupped  appearance  is  easily  explained  by  the  greater  power 
of  contraction  possessed  by  the  fibrin  of  inflammatory  blood 
arid  by  its  contraction  being  now  not  interfered  with  by  the 
presence  of  red  corpuscles  in  its  meshes. 

Although  the  appearance  just  described  is  commonly  the  re- 
sult of  a  condition  of  the  blood  in  which  there  is  an  increase 
in  the  quantity  of  fibrin,  it  need  not  of  necessity  be  so.  For  a 
very  different  state  of  the  blood,  such  as  that  which  exists  in 
chlorosis,  may  give  rise  to  the  same  appearance ;  but  in  this 
case  the  pale  layer  is  due  to  a  relatively  smaller  amount  of  red 
corpuscles,  not  to  any  increase  in  the  quantity  of  fibrin. 

It  is  thus  evident  that  the  coagulation  of  the  blood  is  due 
to  its  fibrin.  The  cause  of  the  coagulation  of  the  fibrin,  how- 
ever, is  still  a  mystery. 

The  theory  of  Prof.  Lister,  that  fibrin  has  no  natural  ten- 
dency to  clot,  but  that  its  coagulation  out  of  the  body  is  due 
to  the  action  of  foreign  matter  with  which  it  happens  to  be 
brought  into  contact,  and,  in  the  body,  to  conditions  of  the 
tissues,  which  cause  them  to  act  towards  it  like  foreign  matter, 
is  insufficient;  because  even  if  it  be  true,  it  still  leaves  unex- 
plained the  manner  in  which  the  fibrin,  fluid  in  the  living 
bloodvessels,  can,  by  foreign  matter,  be  thus  made  solid.  If 
it  be  a  fact,  it  is  a  very  important  one,  but  it  is  not  an  expla- 
nation. 

The  same  remark  may  be  applied  also  to  another  theory 
which  differs  from  the  last,  in  that  while  it  admits  a  natural 
tendency  on  the  part  of  the  blood  to  coagulation,  it  supposes 
that  this  tendency  in  the  living  body  is  restrained  by  some  in- 
hibitory power  resident  in  the  walls  of  the  containing  vessels. 
This  also  may,  or  may  not,  be  true;  but  it  is  only  a  statement 
of  a  possible  fact,  and  leaves  unexplained  the  manner  in  which 
living  tissue  can  thus  restrain  coagulation. 

Dr.  Draper  believes  that  coagulation  takes  place  in  the  liv- 
ing body,  as  out  of  it,  or  as  in  the  dead  ;  but  in  the  one  case 
the  fibrin  is  picked  out  in  the  course  of  the  circulation  by  tis- 


COAGULATION    OF    BLOOD.  61 

sues  which  this  particular  constituent  of  the  blood  is  destined 
to  nourish ;  in  the  others,  it  remains  and  becomes  evident  as  a 
clot.  This  explanation  is  ingenious,  but  requires  some  kind  of 
proof  before  it  can  be  adopted. 

Concerning  other  theories,  as  for  instance,  that  coagulation 
is  due  to  the  escape  of  carbonic  acid,  or  of  ammonia,  it  need 
only  be  said  that  they  have  been  completely  disproved. 

We  must  therefore,  for  the  present,  believe  that  the  cause 
of  the  coagulation  of  the  blood  has  yet  to  be  discovered ;  but 
some  very  interesting  observations  in  connection  with  the  sub- 
ject have  been  recently  made,  and  seem  not  unlikely  to  lead 
in  time  to  a  solution  of  this  difficult  and  most  vexed  question. 
The  observations  referred  to  have  been  made  independently 
by  Alexander  Schmidt,  although  he  was  forestalled  in  regard 
to  some  of  his  experiments  by  Dr.  Andrew  Buchanan,  of  Glas- 
gow, many  years  ago. 

When  blood-serum,  or  washed  blood-clot,  is  added  to  the 
fluid  of  hydrocele,  or  any  other  serous  effusion,  it  speedily 
causes  coagulation,  and  the  production  of  true  fibrin.  And 
this  phenomenon  occurs  also  on  the  admixture  of  serous  effu- 
sions from  different  parts  of  the  body,  as  that  of  hydrocele  with 
that  of  ascites,  or  of  either  with  fluid  from  the  cavity  of  the 
pleura.  Other  substances  also,  as  muscular  or  nervous  tissue, 
skin,  &c.,  have  been  found  also  able  to  excite  coagulation  in 
serous  fluids.  Thus,  fluids  which  have  little  or  no  tendency  to 
coagulate  when  left  to  themselves,  can  be  made  to  produce  a 
clot,  apparently  identical  with  the  fibrin  of  blood  by  the  addi- 
tion to  them  of  matter  which,  on  its  part,  was  not  known  to 
have  any  special  relation  to  fibrin.  As  may  be  supposed,  the 
coagulation  is  not  alike  in  extent  under  all  these  circumstances. 
Thus,  although  it  occurs  when  apparently-few  or  no  blood-cells 
exist  in  either  constituent  of  the  mixture,  yet  the  addition  of 
these  very  much  increases  the  effect,  and  their  presence  evi- 
dently has  a  very  close  connection  with  the  process.  From  the 
action  of  the  buffy  coat  of  a  clot,  in  causing  the  appearance  of 
fibrin  in  serous  effusions,  it  may  be  inferred  that  the  pale  as 
well  as  the  red  corpuscles  are  influential  in  coagulation  under 
these  circumstances.  Blood-crystals  are  also  found  to  be  effec- 
tive in  producing  a  clot  in  serous  fluids. 

The  true  explanation  of  these  very  curious  phenomena  is, 
probably,  not  fully  known ;  but  Schmidt  supposes  that  in 
the  act  of  formation  of  fibrin  there  occurs  the  union  of  two 
substances,  which  he  terms  fibrinoplastin  and  fibrinogen. 

The  substance  which  he  terms  fibrmoplastin,  and  which  he 
has  obtained,  not  only  from  blood,  but  from  many  other  liquids 


62  THE     BLOOD. 

and  solids,  as  the  crystalline  lens,  chyle  and  lymph,  connec- 
tive tissue,  &c.,  which  are  found  capable  of  exciting  coagula- 
tion in  serous  fluids,  is  probably  identical  with  the  globulin  of 
the  red  corpuscles. 

The  fibrinogenous  matter  obtained  from  serous  effusions  dif- 
fers but  little,  chemically,  from  the  fibrinoplastin. 

Thus  in  the  experiment  before  mentioned,  the  globulin  or 
fibrinoplastic  matter  of  the  blood-cells  in  the  clot  causes  co- 
agulation by  uniting  with  the  fibrinogen  present  in  the  hydro- 
cele-fluid.  And  whenever  there  occurs  coagulation  with  the 
production  of  fibrin,  whether  in  ordinary  bloodclotting,  or  in 
the  admixture  of  serous  effusions,  or  in  any  other  way,  a  like 
union  of  these  two  substances  may  be  supposed  to  occur. 

The  main  result,  therefore,  of  these  very  interesting  experi- 
ments and  observations  has  been  to  make  it  probable  that  the 
idea  of  fibrin  existing  in  a  liquid  state  in  the  blood  is  founded 
on  a  mistaken  notion  of  its  real  nature,  and  that,  probably,  it 
does  not  exist  at  all  in  solution  as  fibrin,  but  is  formed  at  the 
moment  of  coagulation  by  the  union  of  two  substances  which, 
in  fluid  blood,  exist  separately. 

The  theories  before  referred  to,  concerning  the  coagulation 
of  the  blood,  will  therefore,  if  this  be  true,  resolve  themselves 
into  theories  concerning  the  causes  of  the  union  of  fibrino- 
plastin and  fibrinogen ;  and  whether,  on  the  one  hand,  it  is  an 
inhibitory  action  of  the  living  bloodvessels  that  naturally  re- 
drains,  or  a  catalytic  action  of  foreign  matter  that  excites,  the 
union  of  these  two  substances. 


Conditions  affecting  Coagulation. 

Although  the  coagulation  of  fibrin  appears  to  be  sponta- 
neous, yet  it  is  liable  to  be  modified  by  the  conditions  in 
which  it  is  placed;  such  as  temperature,  motion,  the  access 
of  air,  the  substances  with  which  it  is  in  contact,  the  mode,  of 
death,  &c.  All  these  conditions  need  to  be  considered  in  the 
study  of  the  coagulation  of  the  blood. 

The  coagulation  of  the  blood  is  hastened  by  the  following 
means : 

1.  Moderate  warmth, — from  about  100°  F.  to  120°  F. 

2.  Rest  is  favorable  to  the  coagulation  of  blood.     Blood,  of 
which   the  whole  mass  is  kept  in  uniform  motion,  as  when  a 
closed  vessel  completely  filled  with  it  is  constantly  moved,  co- 
agulates very  slowly  and  imperfectly.     But  rest  is  not  essen- 
tial to  coagulation ;  for  the  coagulated  fibrin  may  be  quickly 


CONDITIONS    AFFECTING    COAGULATION.       63 

obtained  from  blood  by  stirring  it  with  a  bundle  of  small 
twigs ;  and  whenever  any  rough  points  of  earthy  matter  or 
foreign  bodies  are  introduced  into  the  bloodvessels,  the  blood 
soon  coagulates  upon  them. 

3.  Contact  with  foreign  matter,  and  especially  multiplica- 
tion of  the  points  of  contact.     Thus,  when  all  other  conditions 
are  unfavorable,  the  blood  will  coagulate  upon  rough  bodies 
projecting   into  the  vessels  ;   as,  for  example,   upon  threads 
passed  through  arteries  or  aneurismal  sacs,    or  the   heart's 
valves  roughened  by  inflammatory  deposits  or  calcareous  ac- 
cumulations.    And,  perhaps,  this  may  explain  the  quicker  co- 
agulation of  blood  after  death  in  the  heart  with  walls  made 
irregular  by  the  fleshy  columns,  than  in  the  simple  smooth- 
walled  arteries  and  veins. 

4.  The  free  access  of  air. 

5.  Coagulation  is  quicker  in  shallow  than  in  tall  and  nar- 
row vessels. 

6.  The  addition  of  less  than  twice  the  bulk  of  water. 

The  blood  last  drawn  is  said  to  coagulate  more  quickly  than 
that  which  is  first  let  out. 

The  coagulation  of  the  blood  is  retarded  by  the  following 
means : 

1.  Cold  retards  the  coagulation  of  blood;  and  it  is  said  that, 
so  long  as  blood  is  kept  at  a  temperature  below  40°  F.,  it  will 
not  coagulate  at  all.     Freezing  the  blood,  of  course,  prevents 
its  coagulation  ;  yet  it  will  coagulate,  though  not  firmly,  if 
thawed  after  being  frozen ;  and  it  will  do  so,  even  after  it  has 
been  frozen  for  several  months.     Coagulation  is  accelerated, 
but  the  subsequent  contraction  of  the  clot  is  hindered  by  a 
temperature  between  100°  and  120°  :  a  higher  temperature  re- 
tards coagulation,  or,  by  coagulating  the  albumen  of  the  serum, 
prevents  it  altogether. 

2.  The  addition  of  water  in  greater  proportion  than  twice 
the  bulk  of  the  blood. 

3.  Contact  with  living  tissues,  and  especially  with  the  interior 
of  a  living  bloodvessel,  retards  coagulation,  although  if  the 
blood  be  at  rest  it  does  not  prevent  it. 

4.  The  addition  of  the  alkaline  and  earthy  salts  in  the  pro- 
portion of  2  or  3  per  cent,  and  upwards.    When  added  in  large 
proportion  most  of  these  saline  substances  prevent  coagulation 
altogether.      Coagulation,  however,  ensues  on  dilution    with 
water.     The  time  that  blood  can  be  thus  preserved  in  a  liquid 
state  and  coagulated  by  the  addition  of  water,  is  quite  in- 
definite. 


64  THEBLOOD. 

5.  Imperfect  aeration, — as  in  the  blood  of  those  who  die  by 
asphyxia. 

6.  In  inflammatory  states  of  the  system,  the  blood  coagulates 
more  slowly  although  more  firmly. 

7.  Coagulation  is  retarded  by  exclusion  of  the  blood  from 
the  air,  as  by  pouring  oil  on  the  surface,  &c.     In  vacuo,  the 
blood  coagulates  quickly ;  but  Prof.   Lister  thinks  that  the 
rapidity  of  the  process  is  due  to  the  bubbling  which  ensues 
from  the  escape  of  gas,  and   to  the  blood  being  thus  brought 
more  freely  into  contact  with  the  containing  vessel. 

The  coagulation  of  the  blood  is  prevented  altogether  by  the 
addition  of  strong  acids  and  caustic  alkalies. 

It  has  been  believed,  and  chiefly  on  the  authority  of  Mr. 
Hunter,  that,  after  certain  modes  of  death,  the  blood  does  not 
coagulate  ;  he  enumerates  the  death  by  lightning,  overexertion 
(as  in  animals  hunted  to  death),  blows  on  the  stomach,  fits  of 
anger.  He  says,  "I  have  seen  instances  of  them  all."  Doubt- 
less he  had  done  so ;  but  the  results  of  such  events  are  not  con- 
stant. The  blood  has  been  often  observed  coagulated  in  the 
bodies  of  animals  killed  by  lightning  or  an  electric  shock  ;  and 
Mr.  Gulliver  has  published  instances  in  which  he  found  clots 
in  the  hearts  of  hares  and  stags  hunted  to  death,  and  of  cocks 
killed  in  fighting. 

Chemical  Composition  of  the  Blood. 

Among  the  many  analyses  of  the  blood  that  have  been  pub- 
lished, some,  in  which  all  the  constituents  are  enumerated,  are 
inaccurate  in  their  statements  of  the  proportions  of  those  con- 
stituents ;  others,  admirably  accurate  in  some  particulars,  are 
incomplete.  The  two  following  tables,  constructed  chiefly  from 
the  analyses  of  Denis,  Lecanu,  Simon,  Nasse,  Lehmann,  Bec- 
querel,  Rodier,  and  Gavarret,  are  designed  to  combine,  as  far 
as  possible,  the  advantage  of  accuracy  in  numbers  with  the  con- 
venience of  presenting  at  one  view,  a  list  of  all  the  constituents 
of  the  blood. 

Average  proportions  of  the  principal  constituents  of  the  blood 
in  1000  parts: 


Water, 

lied  corpuscles  (solid  residue), 
Albumen  of  serum, 
Saline  matters,      .... 
Extractive,  fatty,  and  other  matters, 
Fibrin.  . 


784. 

130. 

70. 


6.03 

7.77 
2.2 


1000. 


COMPOSITION     OF     BLOOD.  65 

Average  proportions  of  all  the  constituents  of  the  blood  in 
1000  parts: 

Water, 784. 

Albumen,  .........  70. 

Fibrin, 2.2 

Ked  corpuscles   (dry),         ......  130. 

Fatty  matters, 1.4 

Inorganic  Salts:   Chloride  of  sodium,         .          .         .          3.6 
Chloride  of  potassium,   .         .         .         0.35 
Tribasic  phosphate  of  soda,    .         .         0.2 
Carbonate  of  soda, .         .         .         .         0.28 
Sulphate  of  soda,    ....         0.28 
Phosphates  of  lime  and  magnesia,         0.25 
Oxide  and  phosphate  of  iron,         .         0.5 

Extractive  matters,  biliary  coloring  matter,  gases, 

and  accidental  substances,      .....         6.40 

1000. 

Elementary  composition  of  the  dried  blood  of  the  ox  : 

Carbon, 57.9 

Hydrogen, 7.1 

Nitrogen,       .........  17.4 

Oxygen, 19.2 

Ashes,   ..........  4.4 

These  results  of  the  ultimate  analysis  of  ox's  blood  afford  a 
remarkable  illustration  of  its  general  purpose,  as  supplying  the 
materials  for  the  renovation  of  all  the  tissues.  For  the  analysts 
(Playfair  and  Boeckmann)  have  found  that  the  flesh  of  the  ox 
yields  the  same  elements  in  so  nearly  the  same  proportions  that 
the  elementary  composition  of  the  organic  constituents  of  the 
blood  and  flesh  may  be  considered  identical,  and  may  be  rep- 
resented for  both  by  the  formula  C45H39N6O15. 


The  Blood-  Corpuscles  or  Blood-  Cells. 

It  has  been  already  said  that  the  clot  of  blood  contains, 
with  the  fibrin  and  the  portion  of  the  serum  that  is  soaked  in 
it,  the  blood-corpuscles,  or  blood-cells.  Of  these  there  are  two 
principal  forms,  the  red  and  the  white  corpuscles.  When 
coagulation  has  taken  place  quickly,  both  kinds  of  corpuscles 
may  be  uniformly  diffused  through  the  clot ;  but,  when  it  has 
been  slow,  the  red  corpuscles,  being  the  heaviest  constituent  of 
the  blood,  tend  by  gravitation  to  accumulate  at  the  bottom  of 
the  clot;  and  the  white  corpuscles,  being  among  the  lightest 
constituents,  collect  in  the  upper  part,  and  contribute  to  the 
formation  of  the  bufly  coat. 


66 


THE     BLOOD. 


FIG.  24. 
Mammals.      Birds.         Reptiles.  Amphibia. 


Fish. 


The  above  illustration  is  somewhat  altered  from  a  drawing,  by  Mr.  Gulliver,  in  the 
Proceed.  Zool.  Society,  and  exhibits  the  typical  characters  of  the  red  blood-cells  in 
the  main  divisions  of  the  Vertebrata.  The  fractions  are  those  of  an  inch,  and  rep- 
resent the  average  diameter.  In  the  case  of  the  oval  cells,  only  the  long  diameter  is 
here  given.  It  is  remarkable,  that  although  the  size  of  the  red  blood-cells  varies  so 
much  in  the  different  classes  of  the  vertebrate  kingdom,  that  of  the  white  corpuscles 
remains  comparatively  uniform,  and  thus  they  are,  in  some  animals,  much  greater, 
in  others  much  less,  than  the  red  corpuscles  existing  side  by  side  with  them. 

It  may  be  here  remarked,  that  the  appearance  of  a  nucleus  in  the  red  blood-cells 
of  birds,  reptiles,  amphibia,  and  fish,  has  been  shown  by  Mr.  Savory  to  be  the  result 
of  post-mortem  change;  no  nucleus  being  visible  in  the  cells  as  they  circulate  in  the 
living  body,  or  in  those  which  have  just  escaped  from  the  bloodvessels. 


RED     BLOOD-CORPUSCLES.  67 

The  human  red  blood-cell*  or  blood-corpuscles  (Figs.  25  and 
29)  are  circular  flattened  disks  of  different  sizes,  the  majority 
varying  in  diameter  from  3^00  to  4$^  of  an  inch,  and  about 
TOtWfi  °f  an  incn  in  thickness.  When  viewed  singly,  they  ap- 


pear of  a  pale  yellowish  tinge;  the  deep  red  color  which  they 
give  to  the  blood  being  observable  in  them  only  when  they  are 
seen  en  masse.  Their  borders  are  rounded  ;  their  surfaces,  in 
the  perfect  and  most  usual  state,  slightly  concave;  but  they 
readily  acquire  flat  or  convex  surfaces  when,  the  liquor  san- 
guinis  being  diluted,  they  are  swollen  by  absorption  of  fluid. 
They  are  composed  of  a  colorless,  structureless,  and  transparent 
filmy  framework  or  stroma,  infiltrated  in  all  parts  by  a  red 
coloring-matter  termed  hcemoglobin.  The  stroma  is  tough  and 
elastic,  so  that,  as  the  cells  circulate,  they  admit  of  elongation 
and  other  changes  of  form,  in  adaptation  to  the  vessels,  yet 
recover  their  natural  shape  as  soon  as  they  escape  from  com- 
pression. The  term  cell,  in  the  sense  of  a  bag  or  sac,  is  inap- 
plicable to  the  red  blood-corpuscle  ;  and  it  must  be  considered, 
if  not  solid  throughout,  yet  as  having  no  such  variety  of  con- 
sistence in  different  parts  as  to  justify  the  notion  of  its  being  a 
membranous  sac  with  fluid  contents.  The  stroma  exists  in  all 
parts  of  its  substance,  and  the  coloring  matter  uniformly  per- 
vades this,  and  is  not  merely  surrounded  by  and  mechanically 
inclosed  within  the  outer  wall  of  the  corpuscle.  The  red  cor- 
puscles have  no  nuclei,  although  in  their  usual  state,  the  un- 
equal refraction  of  transmitted  light  gives  the  appearance  of  a 
central  spot,  brighter  or  darker  than  the  border,  according  as  it 
is  viewed  in  or  out  of  focus.  Their  specific  gravity  is  about  1088. 
In  examining  a  number  of  red  corpuscles  with  the  micro- 
scope, it  is  easy  to  observe  certain  natural  diversities  among 
them,  though  they  may  have  been  all  taken  from  the  same 
part.  The  great  majority,  indeed,  are  very  uniform;  but  some 
are  rather  larger,  and  the  larger  ones  generally  appear  paler 
and  less  exactly  circular  than  the  rest  ;  their  surfaces  also  are 
usually  flat  or  slightly  convex,  they  often  contain  a  minute 
shining  particle  like  a  nucleolus,  and  they  are  lighter  than  the 
rest,  floating  higher  in  the  fluid  in  which  they  are  placed. 
Other  deviations  from  the  general  characters  assigned  to  the 
corpuscles  depend  on  changes  that  occur  after  they  are  taken 
from  the  body.  Very  commonly  they  assume  a  granulated  or 
mulberry-like  form,  in  consequence,  apparently,  of  a  peculiar 
corrugation  of  their  cell-walls.  Sometimes,  from  the  same 
cause,  they  present  a  very  irregular,  jagged,  indented,  or  star- 
like  appearance.  The  larger  cells  are  much  less  liable  to  this 
change  than  the  smaller,  and  the  natural  shape  may  be  restored 
by  diluting  the  fluid  in  which  the  corpuscles  float  ;  by  such 


68  THE    BLOOD. 

dilution  the  corpuscles,  as  already  said,  may  be  made  to  swell 
up,  by  absorbing  the  fluid ;  and,  if  much  water  be  added,  they 
will  become  spherical  and  pellucid,  their  coloring-matter  being 
dissolved,  and,  as  it  were,  washed  out  of  them.  Some  of  them 
may  thus  be  burst;  the  others  are  made  obscure;  but  many  of 
these  latter  may  be  brought  into  view  again  by  evaporating, 
or  adding  saline  matter  to,  the  fluid,  so  as  to  restore  it  to  its 
previous  density.  The  changes  thus  produced  by  water  are 
more  quickly  effected  by  weak  acetic  acid,  which  immediately 
makes  the  corpuscles  pellucid,  but  dissolves  few  or  none  of 
them,  for  the  addition  of  an  alkali,  so  as  to  neutralize  the  acid, 
will  restore  their  form  though  not  their  color. 

A  peculiar  property  of  the  red  corpuscles,  which  is  exag- 
gerated in  inflammatory  blood,  and  which  appears  to  exist  in 
a  marked  degree  in  the  blood  of  horses,  may  be  here  noticed. 
It  gives  them  a  great  tendency  to  adhere  together  in  rolls  or 
columns,  like  piles  of  coin,  and  then,  very  quickly,  these  rolls 
fasten  together  by  their  ends,  and  cluster ;  so  that,  when  the 
blood  is  spread  out  thinly  on  a  glass,  they  form  a  kind  of  ir- 
regular network,  with  crowds  of  corpuscles  at  the  several  points 

corresponding  with  the  knots  of  the 
FIG.  25.  net   (Fig.   25).      Hence,   the   clot 

formed  in  such  a  thin  layer  of  blood 
looks  mottled  with  blotches  of  pink 
upon  a  white  ground ;  in  a  larger 
quantity  of  such  blood,  as  soon  as 
the  corpuscles  have  clustered  and 
collected  in  rolls  (that  is,  generally 
in  two  or  three  minutes  after  the 
blood  is  drawn),  they  begin  to  sink 
very  quickly;  for  in  the  aggregate 
Red  corpuscles  collected  into  they  present  less  surface  to  the  re- 
roils  (after  Henie).  sistance  of  the  liquor  sanguinis  than 
they  would  if  sinking  separately. 

Thus  quickly  sinking,  they  leave  above  them  a  layer  of  liquor 
sanguinis,  and  this  coagulating,  forms  a  buffy  coat,  as  before 
described,  the  volume  of  which  is  augmented  by  the  white 
corpuscles,  which  have  no  tendency  to  adhere  to  the  red  ones, 
and  by  their  lightness  float  up  clear  of  them. 

Chemical  Composition  of  Red  Blood-cells. 

It  has  been  before  remarked,  that  the  red  blood-corpuscles 
are  formed  of  a  colorless  stroma,  infiltrated  with  a  coloring 
matter  termed  hcemoglobin.  As  they  exist  in  the  blood,  they 
contain  about  three-fourths  of  their  weight  of  water. 

The  stroma  appears  to  be  composed  of  a  nitrogenous  prox- 


BLOOD-CRYSTALS.  69 

imate  principle  termed  protagon,  combined  with  albuminous 
matter  (paraglobulin  or  fibrinoplastin),  fatty  matters  includ- 
ing cholesterin,  and  salts,  chiefly  phosphates,  of  potash,  soda, 
and  lime. 

Haemoglobin,  which  enters  far  more  largely  into  the  compo- 
sition of  the  red  corpuscles  than  any  other  of  their  constituents, 
is  allied  to  albumen  in  some  respects,  but  differs  remarkably 
from  it  in  others.  One  of  its  most  marked  distinctive  charac- 
ters is  its  tendency  under  certain  artificial  conditions  to  crys- 
tallize ;  the  so-called  blood-crystals  being  but  the  natural  crys- 
talline forms  assumed  by  this  substance. 

Haemoglobin  can  be  obtained  in  a  crystalline  form,  with 
various  degrees  of  difficulty,  from  the  blood  of  different  ani- 
mals, that  of  man  holding  an  intermediate  place  in  this  re- 
spect. Among  the  animals  whose  blood-coloring  matter  crys- 
tallizes most  readily  are  the  guinea-pig  and  the  dog ;  and  in 
these  cases,  to  obtain  crystals,  it  is  generally  sufficient  to  dilute 
a  drop  of  recently  drawn  blood  with  water,  and  expose  it  for  a 
few  minutes  to  the  air.  In  many  instances,  however,  a  some- 
what less  simple  process  must  be  adopted ;  as  the  addition  of 
chloroform  or  ether,  rapid  freezing  and  then  thawing,  or  other 
means  which  separate  the  coloring  matter  from  the  other  con- 
stituents of  the  corpuscles. 

Different  forms  of  blood-crystals  are  shown  in  the  accom- 
panying figures. 


Prismatic,  from  human  blood. 

Another  and  most  important  character  of  haemoglobin  is 
its  attraction  for  oxygen,  and  some  other  gases,  as  carbonic  and 

1  Figs.  26,  27,  and  28,  illustrate  some  of  the  principal  forms  of 
blood-crj'stals. 


70 


THE    BLOOD. 


nitrous  oxides,  with  all  of  which  it  appears  to  form  definite 
chemical  combinations.  The  combination  with  oxygen  is  that 
which  is  of  most  physiological  inportance.  During  the  passage 
of  the  blood  through  the  lungs,  it  is  constantly  formed;  while 
it  is  as  constantly  decomposed,  in  consequence  of  the  readiness 
with  which  haemoglobin  parts  with  oxygen,  when  the  latter  is 

FIG.  27. 


Tetrahedral,  from  blood  of  the  guinea-pig. 

exposed  to  other  attractions  in  its  circulation  through  the  sys- 
temic capillaries.  Thus,  the  red  corpuscles,  in  virtue  of  their 
coloring  matter,  which  readily  absorbs  oxygen  and  as  readily 


FIG.  28. 


Hexagonal  crystals,  from  blood  of  squirrel.     On  these  six-sided  plates,  prismatic 
crystals,  grouped  in  a  stellate  manner,  not  unfrequently  occur  (after  Funke). 


WHITE    COEPUSCLES. 


71 


gives  it  up  again,  are  the  chief  means  by  which  oxygen  is 
carried  in  the  blood  (see  also  p.  75). 

By  heat,  mineral  and  other  acids,  alkalies,  &c.,  haemoglobin 
is  decomposed  into  an  albuminous  matter  (resembling  glob- 
ulin) 'and  hcematin.  The  latter,  now  known  to  be  a  product 
of  the  decomposition  of  haemoglobin,  was  once  thought  to  be 
the  natural  coloring  matter  of  the  blood. 

The  White  Corpuscles  of  the  Blood  or  Blood  Leucocytes. 

The  white  corpuscles  are  much  less  numerous  than  the  red. 
On  an  average,  in  health,  there  may  be  one  white  to  400  or 
500  red  corpuscles ;  but  in  disease,  the  proportion  is  often  as 
high  as  one  to  ten,  and  sometimes  even  much  higher. 

In  health,  the  proportion  varies  considerably  even  in  the 
course  of  the  same  day.  The  variations  appear  to  depend 
chiefly  on  the  amount,  and  probably  also  on.  the  kind  of  food 
taken ;  the  number  of  leucocytes  being  very  considerably  in- 
creased by  a  meal,  and  diminished  again  on  fasting. 

They  present  greater  diversities  of  form  than  the  red  ones 
do ;  but  the  gradations  between  the  extreme  forms  are  so 
regular,  that  no  sufficient  reason  can  be  found  for  supposing 
that  there  is  in  healthy  blood  more  than  one  species  of  white 
corpuscles.  In  their  most  general  appearance  they  are  circular 
and  nearly  spherical,  about  ^^  of  an  inch  in  diameter  (Fig. 
29).  They  have  a  grayish,  pearly  look,  appearing  variously 
shaded  or  nebulous,  the  shading  being  much  darker  in  some 
than  in  others.  They  seem  to  be  formed  of  protoplasm  (p.  26), 
containing  granules  which  are 
in  some  specimens  few  and 
very  distinct,  in  others 
(though  rarely)  so  numerous 
that  the  whole  corpuscle  looks 
like  a  mass  of  granules. 

These  corpuscles  cannot  be 
said  to  have  any  true  cell- 
wall.  In  a  few  instances  an 
apparent  cell-membrane  can 
be  traced  around  them ;  but, 
much  more  commonly,  even 
this  is  not  discernible  till  after 
the  addition  of  water  or  di- 
lute acetic  acid,  which  pen- 
etrates the  corpuscle,  and  lifts 
up  and  distends  what  looks  *ed  and  wh*te  Wood-corpuscles  A, 

,.V  11         11  ,1  White    corpuscle   of   natural  aspect;  B, 

like    a    Cell-Wall,    tO    the    m-    Three  white  corpuscles  acted  on  by  weak 
terior  of  which   the   material,    acetic  acid,    c,  Red  blood-corpuscles. 


FIG.  29. 


72  THE    BLOOD. 

that  before  appeared  to  form  the  whole  corpuscle,  remains 
attached  as  the  nucleus  of  the  cell  (Fig.  29). 

A  remarkable  property  of  the  white  corpuscles,  first  observed 
by  Mr.  Wharton  Jones,  consists  in  their  capability  of  assuming 
different  forms,  irrespective  of  any  external  influence.  If  a 
drop  of  blood  be  examined  with  a  high  microscope  power 
under  conditions  by  which  loss  of  moisture  is  prevented,  at 
the  same  time  that  the  temperature  is  maintained  at  about  the 
degree  natural  to  the  blood  as  it  circulates  in  the  living  body, 
the  leucocytes  can  be  seen  alternately  contracting  and  dilating 
very  slowly  at  various  parts  of  their  circumference — shooting 
out  irregular  processes,  and  again  withdrawing  them  partially 
or  completely,  and  thus  in  succession  assuming  various  irreg- 
ular forms. 

These  movements,  called  amoeboid,  from  their  resemblance  to 
the  movements  exhibited  by  an  animal  called  the  Amoeba,  the 
structure  of  which  is  as  simple  as  that  of  a  white  blood-cor- 
puscle, are  characteristic  of  the  living  leucocyte,  and  form  a 
good  example  of  the  contractile  property  of  protoplasm,  before 
referred  to.  Indeed,  the  unchanging  rounded  form  which  the 
corpuscles  present  in  specimens  of  blood  examined  in  the 
ordinary  manner  under  the  microscope,  must  be  looked  upon 
as  the  shape  natural  to  a  dead  corpuscle,  or  one  whose  vitality 
is  dormant,  rather  than  as  the  proper  shape  of  one  living  and 
active. 

Besides  the  red  and  white  corpuscles,  the  microscope  reveals 
numerous  minute  molecules  or  granules  in  the  blood,  circular 
or  spherical,  and  varying  in  size  from  the  most  minute  visible 
speck  to  the  -g^1^  of  an  inch  (Gulliver).  These  molecules 
are  very  similar  to  those  found  in  the  lymph  and  chyle,  and 
are,  some  of  them,  fatty,  being  soluble  in  ether,  others  prob- 
ably albuminous,  being  soluble  in  acetic  acid.  Generally,  also, 
there  may  be  detected  in  the  blood,  especially  during  the 
height  of  digestion,  very  minute  equal-sized  fatty  particles, 
similar  to  those  of  which  the  molecular  base  of  chyle  is  con- 
stituted (Gulliver). 

The  Serum. 

The  serum  is  the  liquid  part  of  the  blood  remaining  after 
the  coagulation  of  the  fibrin.  In  the  usual  mode  of  coagula- 
tion, part  of  the  serum  remains  soaked  in  the  clot,  and  the  rest, 
squeezed  from  the  clot  by  its  contraction,  lies  around  and  over 
it.  The  quantity  of  serum  that  appears  around  the  clot  "de- 
pends partly  on  the  total  quantity  in  the  blood,  but  partly 
also  on  the  degree  to  which  the  clot  contracts.  This  is  affected 
by  many  circumstances :  generally,  the  faster  the  coagulation 


SERUM    OF    BLOOD.  73 

the  less  is  the  amount  of  contraction ;  and,  therefore,  when 
blood  coagulates  quickly,  it  will  appear  to  contain  a  small 
proportion  of  serum.  Hence,  the  serum  always  appears  de- 
ficient in  blood  drawn  slowly  into  a  shallow  vessel,  abundant 
in  inflammatory  blood  drawn  into  a  tall  vessel.  In  all  cases, 
too,  it  should  be  remembered,  that  since  the  contraction  of  the 
clot  may  continue  for  thirty-six  or  more  hours,  the  quantity 
of  serum  in  the  blood  cannot  be  even  roughly  estimated  till 
this  period  has  elapsed. 

The  serum  is  an  alkaline,  slimy  or  viscid,  yellowish  fluid, 
often  presenting  a  slight  greenish,  or  grayish  hue,  and  with  a 
specific  gravity  of  from  1025  to  1030.  It  is  composed  of  a 
mixture  of  various  substances  dissolved  in  about  nine  times 
their  weight  of  water.  It  contains,  indeed,  the  greater  part  of 
all  the  substances  enumerated  as  existing  in  the  blood,  with 
the  exception  of  the  fibrin  and  the  red  corpuscles.  Its  prin- 
cipal constituent  is  albumen,  of  which  it  contains  about  8  per 
cent.,  and  the  coagulation  of  which,  when  heated,  converts 
nearly  the  whole  of  the  serum  into  a  solid  mass.  The  liquid 
which  remains  uncoagulated,  and  which  is  often  inclosed  in 
little  cavities  in  the  coagulated  serum,  is  called  serosity;  it  con- 
tains, dissolved  in  water,  fatty,  extractive,  and  saline  matters. 

Variations  in  the  principal  Constituents  of  the  Liquor  Sanguinis. 

The  water  of  the  blood  is  subject  to  hourly  variations  in  its 
quantity,  according  to  the  period  since  the  taking  of  food,  the 
amount  of  bodily  exercise,  the  state  of  the  atmosphere,  and  all 
the  other  events  that  may  affect  either  the  ingestion  or  the 
excretion  of  fluids.  According  to  these  conditions,  it  may  vary 
from  700  to  790  parts  in  the  thousand.  Yet  uniformity  is  on 
the  whole  maintained ;  because  nearly  all  those  things  which 
tend  to  lower  the  proportion  of  water  in  the  blood,  such  as 
active  exercise,  or  the  addition  of  saline  and  other  solid  matter, 
excite  thirst ;  while,  on  the  other  hand,  the  addition  of  an  ex- 
cess of  water  to  the  blood  is  quickly  followed  by  its  more 
copious  excretion  in  sweat  and  urine.  And  these  means  for 
adjusting  the  proportion  of  the  water  find  their  purpose  in 
maintaining  certain  important  physical  conditions  in  the 
blood ;  such  as  its  proper  viscidity,  and  the  degree  of  its  ad- 
hesion to  the  vessels  through  which  it  ought  to  flow  with  the 
least  possible  resistance  from  friction.  On  this  also  depends, 
in  great  measure,  the  activity  of  absorption  by  the  bloodves- 
sels, into  which  no  fluids  will  quickly  penetrate,  but  such  as 
are  of  less  density  than  the  blood.  Again,  the  quantity  of 
water  in  the  blood  determines  chiefly  its  volume,  and  thereby 


74  THE     BLOOD. 

the  fulness  and  tension  of  the  vessels  and  the  quantity  of  fluid 
that  will  exude  from  them  to  keep  the  tissues  moist.  Finally, 
the  water  is  the  general  solvent  of  all  the  other  materials  of 
the  liquor  sanguinis. 

It  is  remarkable,  that  the  proportion  of  water  in  the  blood 
may  be  sometimes  increased  even  during  its  abstraction  from 
an  artery  or  vein.  Thus  Dr.  Zimmerman,  in  bleeding  dogs, 
found  the  last  drawn  portion  of  blood  contain  12  or  13  parts 
more  of  water  in  1000  than  the  blood  first  drawn  ;  and  Polli 
noticed  a  corresponding  diminution  in  the  specific  gravity  of 
the  human  blood  during  venesection,  and  suggested  the  only 
probable  explanation  of  the  fact,  namely,  that,  during  bleed- 
ing, the  bloodvessels  absorb  very  quickly  a  part  of  the  serous 
fluid  with  which  all  the  tissues  are  moistened. 

The  albumen  may  vary,  consistently  with  health,  from  60 
to  70  parts  in  the  1000  of  blood.  The  form  in  which  it  exists 
in  the  blood  is  not  yet  certain.  It  may  be  that  of  simple 
solution  as  pure  albumen  ;  but  it  is,  more  probably,  in  combin- 
ation with  soda,  as  an  albuminate  of  soda ;  for,  if  serum  be 
much  diluted  with  water,  and  then  neutralized  with  acetic  acid, 
pure  albumen  is  deposited.  Another  view  entertained  by  En- 
derlin  is  that  the  albumen  is  dissolved  in  the  solution  of  the 
neutral  phosphate  of  sodium,  to  which  he  considers  the  alkaline 
reaction  of  the  blood  to  be  due,  and  solutions  of  which  can 
dissolve  large  quantities  of  albumen  and  phosphate  of  lime. 

The  proportion  of  fibrin  in  healthy  blood  may  vary  between 
2  and  3  parts  in  1000.  In  some  diseases,  such  as  typhus,  and 
others  of  low  type,  it  may  be  as  little  as  1.034;  in  other  dis- 
eases, it  is  said,  it  may  be  increased  to  as  much  as  7.528  parts 
in  1000.  But,  in  estimating  the  quantity  of  fibrin,  chemists 
have  not  taken  account  of  the  white  corpuscles  of  the  blood. 
These  cannot,  by  any  mode  of  analysis  yet  invented,  be  sepa- 
rated from  the  fibrin  of  mammalian  blood  :  their  composition 
is  unknown,  but  their  weight  is  always  included  in  the  estimate 
of  the  fibrin.  In  health  they  may,  perhaps,  add  too  little  to 
its  weight  to  merit  consideration  ;  but  in  many  diseases,  espe- 
cially in  inflammatory  and  other  blood  diseases  in  which  the 
fibrin  is  said  to  be  increased,  these  corpuscles  become  so  numer- 
ous that  a  large  proportion  of  the  supposed  increase  of  the  fibrin 
must  be  due  to  their  being  weighed  with  it.  On  this  account 
all  the  statements  respecting  the  increase  of  fibrin  in  certain 
diseases  need  revision. 

The  enumeration  of  the  fatty  matters  of  the  blood  makes  it 
probable  that  most  of  those  which  are  found  in  the  tissues  or 
secretions  exist  also  ready-formed  in  the  blood;  for  it  contains 
the  cholesterin  of  the  bile,  the  cerebrin  and  phosphorized  fat 


FATTY    MATTERS    IN    THE     BLOOD.  75 

of  the  brain,  and  the  ordinary  saponifiable  fats,  stearin,  olein, 
and  palmitin.  A  volatile  fatty  acid  is  that  on  which  the  odor 
of  the  blood  mainly  depends;  and  it  is  supposed  that  when 
sulphuric  acid  is  added  (see  p.  56),  it  evolves  the  odor  by  com- 
bining with  the  base,  with  which,  naturally,  this  acid  is  neu- 
tralized. According  to  Lehmann,  much  of  the  fatty  matter 
of  the  blood  is  accumulated  in  the  red  corpuscles. 

These  fatty  matters  are  subject  to  much  variation  in  quan- 
tity, being  commonly  increased  after  every  meal  in  which  fat, 
or  starch,  or  saccharine  substances  have  been  taken.  At  such 
times,  the  fatty  particles  of  the  chyle,  added  quickly  to  the 
blood,  are  only  gradually  assimilated  ;  and  their  quantity  may 
be  sufficient  to  make  the  serum  of  the  blood  opaque,  or  even 
milk-like. 

As  regards  the  inorganic  constituents  of  the  blood — the  sub- 
stances which  remain  as  ashes  after  its  complete  burning — one 
may  observe  in  general  their  small  quantity  in  proportion  to 
that  of  the  animal  matter  contained  in  it.  Those  among  them 
of  peculiar  interest  are  the  phosphate  and  carbonate  of  sodium, 
and  the  phosphate  of  calcium.  It  appears  most  probable  that 
the  blood  owes  its  alkaline  reaction  to  both  these  salts  of 
sodium.  The  existence  of  the  neutral  phosphate  (Na2H,PO4) 
was  proved  by  Enderlin:  the  presence  of  carbonate  of  sodium 
has  been  proved  by  Lehmann  and  others. 

In  illustration  of  the  characters  which  the  blood  may  derive 
from  the  phosphate  of  sodium,  Liebig  points  out  the  large  ca- 
pacity which  solutions  of  that  salt  have  of  absorbing  carbonic 
acid  gas,  and  then  very  readily  giving  it  off  again  when  agitated 
in  atmospheric  air,  and  when  the  atmospheric  pressure  is  di- 
minished. It  is  probably,  also,  by  means  of  this  salt,  that  the 
phosphate  of  calcium  is  held  in  solution  in  the  blood  in  a  form 
in  which  it  is  not  soluble  in  water,  or  in  a  solution  of  albu- 
men. Of  the  remaining  inorganic  constituents  of  the  blood, 
the  oxide  and  phosphate  of  iron  referred  to,  exist  in  the  liquor 
sanguinis,  independently  of  the  iron  in  the  corpuscles. 

Schmidt's  investigations  have  shown  that  the  inorganic  con- 
stituents of  the  blood-cells  somewhat  differ  from  those  con- 
tained in  the  serum ;  the  former  possessing  a  considerable  pre- 
ponderance of  phosphates  and  of  the  salts  of  potassium,  while 
the  chlorides,  especially  of  sodium,  with  phosphate  of  sodium, 
are  particularly  abundant  in  the  latter. 

Among  the  extractive  matters  of  the  blood,  the  most  note- 
worthy are  Oreatin  and  Creatinin.  Besides  these,  other  or- 
ganic principles  have  been  found  either  constantly  or  gen- 
erally in  the  blood,  including  casein,  especially  in  women 
during  lactation :  glucose,  or  grape-sugar,  found  in  the  blood 


76  THE     BLOOD. 

of  the  hepatic  vein,  but  disappearing  during  its  transit  through 
the  lungs  (Bernard) ;  urea,  and  in  very  minute  quantities, 
uric  add  (Gar rod);  hippuric  and  lactic  acids;  ammonia  (Rich- 
ardson); and,  lastly,  certain  coloring  and  odoriferous  matters. 

Variations  in  healthy  Blood  under  different  Circumstances. 

As  the  general  condition  of  the  body  depends  so  much  on 
the  condition  of  the  blood,  and  as,  on  the  other  hand,  any- 
thing that  affects  the  body  must  sooner  or  later,  and  to  a 
greater  or  less  degree,  affect  the  blood  also,  it  might  be  ex- 
pected that  considerable  variations  in  the  qualities  of  this  fluid 
would  be  found  under  different  circumstances  of  disease ;  and 
such  is  found  to  be  the  case.  Even  in  health,  however,  the 
general  composition  of  the  blood  varies  considerably. 

The  conditions  which  appear  most  to  influence  the  compo- 
sition of  the  blood  in  health,  are  these :  sex,  pregnancy,  age, 
and  temperament.  The  composition  of  the  blood  is  also,  of 
course,  much  influenced  by  diet. 

1.  Sex. — The  blood  of  men   differs   from   that  of  women, 
chiefly  in  being  of  somewhat  higher  specific  gravity,  from  its 
containing  a  relatively  larger  quantity  of  red  corpuscles. 

2.  Pregnancy. — The  blood  of  pregnant  women  has  a  rather 
lower  specific  gravity  than  the  average,  from  deficiency  of  red 
corpuscles.     The  quantity  of  white  corpuscles,  on  the  other 
hand,  and  of  fibrin,  is  increased. 

3.  Age. — From  the  analysis  of  Denis  it  appears  that  the 
blood  of  the  foetus  is  very  rich  in  solid  matter,  and  especially 
in  red  corpuscles;  and  this  condition,  gradually  diminishing, 
continues  for  some  weeks  after  birth.     The  quantity  of  solid 
matter  then  falls  during  childhood  below  the  average,  again 
rises  during  adult  life,  and  in  old  age  falls  again. 

4.  Temperament. — But  little  more  is  known  concerning  the 
connection  of  this  with   the  condition  of  the  blood,  than  that 
there  appears  to  be  a  relatively  larger  quantity  of  solid  matter, 
and  particularly  of  red  corpuscles,  in  those  of  a  plethoric  or 
sanguineous  temperament. 

5.  Diet. — Such  differences  in  the  composition  of  the  blood 
as  are  due  to  the  temporary  presence  of  various  matters  ab- 
sorbed with  the  food  and  drink,  as  well  as  the  more  lasting 
changes  which  must  result  from  generous  or  poor  diet  respect- 
ively, need  be  here  only  referred  to. 

Effects  of  Bleeding. — The  result  of  bleeding  is  to  diminish 
the  specific  gravity  of  the  blood ;  and  so  quickly,  that  in  a 
single  venesection,  the  portion  of  blood  last  drawrn  has  often 
a  less  specific  gravity  than  that  of  the  blood  that  flowed  first 


VAEIATIONS   IN   COMPOSITION.  77 

(J.  Davy  and  Polli).  This  is,  of  course,  due  to  absorption  of 
fluid  from  the  tissues  of  the  body.  The  physiological  import 
of  this  fact,  namely,  the  instant  absorption  of  liquid  from  the 
tissues,  is  the  same  as  that  of  the  intense  thirst  which  is  so 
common  after  either  loss  of  blood,  or  the  abstraction  from  it 
of  watery  fluid,  as  in  cholera,  diabetes,  and  the  like. 

For  some  little  time  after  bleeding,  the  want  of  red  blood- 
cells  is  well  marked ;  but  with  this  exception,  no  considerable 
alteration  seems  to  be  produced  in  the  composition  of  the  blood 
for  more  than  a  very  short  time,  the  loss  of  the  other  constitu- 
ents, including  the  pale  corpuscles,  being  v.ery  quickly  repaired. 

Variations  in  the  Composition  of  the  Blood,  in  different  Parts  of 
the  Body. 

The  composition  of  the  blood,  as  might  be  expected,  is  found 
to  vary  in  different  parts  of  the  body.  Thus,  arterial  blood 
differs  from  venous ;  and  although  its  composition  and  general 
characters  are  uniform  throughout  the  whole  course  of  the 
systemic  arteries,  they  are  not  so  throughout  the  venous  sys- 
tem— the  blood  contained  in  some  veins  differing  remarkably 
from  that  in  others. 

1.  Differences  between  Arterial  and  Venous  Blood. — These 
maybe  arranged  under  two  heads, — differences  in  color,  and  in 
general  composition. 

a.  Color. — Concerning  the  cause  of  the  difference  in  color 
between  arterial  and  venous  blood,  there  has  been  much  doubt, 
not  to  say  confusion.  For  while  the  scarlet  color  of  the  ar- 
terial blood  has  been  supposed  by  so  me  observers,  and  for  some 
reasons,  to  be  due  to  the  chemical  action  of  oxygen,  and  the 
purple  tint  of  that  in  the  veins  to  the  action  of  carbonic  acid, 
there  are  facts  which  made  it  seem  probable  that  the  cause 
was  a  mechanical  one  rather  than  a  chemical,  and  that  it  de- 
pended on  a  difference  in  the  shape  of  the  red  corpuscles,  by 
which  their  power  of  transmitting  and  reflecting  light  was  al- 
tered. Thus,  carbonic  acid  was  thought  to  make  the  blood 
dark  by  causing  the  red  cells  to  assume  a  biconvex  outline, 
and  oxygen  was  supposed  to  reverse  the  effect  by  contracting 
them  and  rendering  them  biconcave.  We  may  believe,  how- 
ever, that,  at  least  for  the  present,  this  vexed  question  has,  by 
the  results  of  investigations  undertaken  by  Professor  Stokes 
and  others,  been  now  set  at  rest. 

The  coloring  matter  of  the  blood,  or  haemoglobin  (p.  69),  is 
capable  of  existing  in  two  different  states  of  oxidation,  and  the 
respective  colors  of  arterial  and  venous  blood  are  caused  by 
differences  in  tint  between  these  two  varieties— oxidized  or  scar- 


78  THE    BLOOD. 

let  haemoglobin  and  deoxidized  or  purple  haemoglobin.  The 
change  of  color  produced  by  the  passage  of  the  blood  through 
the  lungs,  and  its  consequent  exposure  to  oxygen,  is  due,  prob- 
ably, to  the  oxidation  of  purple,  and  its  conversion  into  scarlet 
haemoglobin;  while  the  readiness  with  which  the  latter  is  de- 
oxidized offers  a  reasonable  explanation  of  the  change,  in  re- 
gard to  tint,  of  arterial  into  venous  blood, — the  transformation 
being  effected  by  the  delivering  up  of  oxygen  to  the  tissues,  by 
the  scarlet  haemoglobin,  during  the  blood's  passage  through 
the  capillaries.  The  changes  of  color  are  more  probably  due 
to  this  cause,  namely,  a  varying  quantity  of  oxygen  chemically 
combined  with  the  haemoglobin,  than  to  any  mechanical  effect 
of  this  gas,  or  to  the  influence  of  carbonic  acid,  either  chemi- 
cally, on  the  coloring  matter,  or  mechanically,  on  the  corpuscles 
which  contain  it.  We  are  not,  perhaps,  in  a  position  to  deny 
altogether  the  possible  influence  of  mechanical  conditions  of 
the  red  corpuscles  on  the  color  of  arterial  and  venous  blood 
respectively ;  but  it  is  probable  that  this  cause  alone  would  be 
quite  insufficient  to  explain  the  differences  in  the  color  of  the 
two  kinds  of  blood,  and  therefore  if  it  be  an  element  at  all  in 
the  change,  it  must  be  allowed  to  take  only  a  subordinate 
position. 

The  distinction  between  the  two  kinds  of  haemoglobin  nat- 
urally present  in  the  blood,  or  in  other  words,  the  proof  that 
the  addition  or  subtraction  of  oxygen  involves  the  production 
respectively  of  two  substances  having  fundamental  differences 
of  chemical  constitution,  has  been  made  out  chiefly  by  spectrum- 
analysis, — the  effects  produced  by  placing  oxidized  and  de- 
oxidized solutions  of  haemoglobin  in  the  path  of  a  ray  of  light 
traversing  a  spectroscope  being  different.  For  while  the  oxi- 
dized solution  causes  the  appearance  of  two  absorption  bands 
in  the  yellow  and  the  green  part  of  the  spectrum,  these  are  re- 
placed by  a  single  band  intermediate  in  position,  when  the  ox- 
idized or  scarlet  solution  is  darkened  by  deoxidizing  agencies, 
or,  in  other  words,  when  the  change  which  naturally  ensues  in 
the  conversion  of  arterial  into  venous  blood  is  artificially  pro- 
duced.1 

The  greater  part  of  the  haemoglobin  in  both  arterial  and 
venous  blood  probably  exists  in  the  scarlet  or  more  highly  ox- 
idized condition,  and  only  a  small  part  is  deoxidized  and  made 
purple  in  its  passage  from  the  arteries  into  the  veins. 

The  differences   in    regard  to  color   between  arterial   and 

1  The  student  to  whom  the  terms  employed  in  connection  with 
spectrum  analysis  are  not  familiar,  is  advised  to  consult,  with  ref- 
erence to  the  preceding  paragraph,  an  elementary  treatise  on  Physics. 


BLOOD  OF  PORTAL  VEIN.  79 

venous  blood  are  sometimes  not  to  be  observed.  If  blood  runs 
very  slowly  from  an  artery,  as  from  the  bottom  of  a  deep  and 
devious  wound,  it  is  often  as  dark  as  venous  blood.  In  persons 
nearly  asphyxiated  also,  and  sometimes,  under  the  influence  of 
chloroform  or  ether,  the  arterial  blood  becomes  like  the  venous. 
In  the  foetus  also  both  kinds  of  blood  are  dark.  But,  in  all 
these  cases,  the  dark  blood  becomes  bright  on  exposure  to  the 
air.  Bernard  has  shown  that  venous  blood  returning  from  a 
gland  in  active  secretion  is  almost  as  bright  as  arterial  blood. 

b.  General  Composition. — The  chief  differences  between  ar- 
terial and  ordinary  venous  blood  are  these.  Arterial  blood 
contains  rather  more  fibrin,  and  rather  less  albumen  and  fat. 
It  coagulates  somewhat  more  quickly.  Also,  it  contains  more 
oxygen,  and  less  carbonic  acid.  According  to  Denis,  the 
fibrin  of  venous  blood  differs  from  arterial,  in  that  when  it  is 
fresh  and  has  not  been  much  exposed  to  the  air,  it  may  be 
dissolved  in  a  slightly  heated  solution  of  nitrate  of  potassium. 

Some  of  the  veins,  however,  contain  blood  which  differs  from 
the  ordinary  standard  considerably.  These  are  the  portal,  the 
hepatic,  and  the  splenic  veins. 

Portal  Vein. — The  blood  which  the  portal  vein  conveys  to 
the  liver  is  supplied  from  two  chief  sources ;  namely,  that  in 
the  gastric  and  mesenteric  veins,  which  contains  the  soluble 
elements  of  food  absorbed  from  the  stomach  and  intestines 
during  digestion,  and  that  in  the  splenic  vein ;  it  must,  there- 
fore, combine  the  qualities  of  the  blood  from  each  of  these 
sources. 

The  blood  in  the  gastric  and  mesenteric  veins  will  vary 
much  according  to  the  stage  of  digestion  and  the  nature  of  the 
food  taken,  and  can  therefore  be  seldom  exactly  the  same. 
Speaking  generally,  and  without  considering  the  sugar,  dex- 
trin, and  other  soluble  matters  which  may  have  been  absorbed 
from  the  alimentary  canal,  this  blood  appears  to  be  deficient 
in  solid  matters,  especially  in  red  corpuscles,  owing  to  dilution 
by  the  quantity  of  water  absorbed,  to  contain  an  excess  of  al- 
bumen, though  chiefly  of  a  lower  kind  than  usual,  resulting 
from  the  digestion  of  nitrogenized  substances,  and  termed  al- 
buminose,  and  to  yield  a  less  tenacious  kind  of  fibrin  than  that 
of  blood  generally. 

The  blood  from  the  splenic  vein  is  probably  more  definite  in 
composition,  though  also  liable  to  alterations  according  to  the 
stage  of  the  digestive  process,  and  other  circumstances.  It 
seems  generally  to  be  deficient  in  red  corpuscles,  and  to  con- 
tain an  unusually  large  proportion  of  albumen.  The  fibrin 
seems  to  vary  in  relative  amount,  but  to  be  almost  always 
above  the  average.  The  proportion  of  colorless  corpuscles  ap- 


80  THE    BLOOD. 

pears  also  to  be  unusually  large.  The  whole  quantity  of  solid 
matter  is  decreased,  the  diminution  appearing  to  be  chiefly  in 
the  proportion  of  red  corpuscles. 

The  blood  of  the  portal  vein,  combining  the  peculiarities  of 
its  two  factors,  the  splenic  and  mesenteric  venous  blood,  is 
usually  of  lower  specific  gravity  than  blood  generally,  is  more 
watery,  contains  fewer  red  corpuscles,  more  albumen,  chiefly 
in  the  form  of  alburninose,  and  yields  a  less  firm  clot  than  that 
yielded  by  other  blood,  owing  to  the  deficient  tenacity  of  its 
fibrin.  These  characteristics  of  portal  blood  refer  to  the  com- 
position of  the  blood  itself,  and  have  no  reference  to  the  ex- 
traneous substances,  such  as  the  absorbed  materials  of  the 
food,  which  it  may  contain ;  neither,  indeed,  has  any  complete 
analysis  of  these  been  given. 

Comparative  analyses  of  blood  in  the  portal  vein  and  blood 
in  the  hepatic  veins  have  also  been  frequently  made,  with  the 
view  of  determining  the  changes  which  this  fluid  undergoes  in 
its  transit  through  the  liver.  Great  diversity,  however,  is  ob- 
servable in  the  analyses  of  these  two  kinds  of  blood  by  dif- 
ferent chemists.  Part  of  this  diversity  is  no  doubt  attributable 
to  the  fact  pointed  out  by  Bernard,  that  unless  the  portal  vein 
is  tied  before  the  liver  is  removed  from  the  body,  hepatic 
venous  blood  is  very  liable  to  regurgitate  into  the  portal  vein, 
and  thus  vitiate  the  result  of  the  analysis.  Guarding  against 
this  source  of  error,  recent  observers  seemed  to  have  deter- 
mined that  hepatic  venous  blood  contains  less  water,  albumen, 
and  salts,  than  the  blood  of  the  portal  vein ;  but  that  it  yields 
a  much  larger  amount  of  extractive  matter,  in  which,  accord- 
ing to  Bernard  and  others,  is  one  constant  element,  namely, 
grape-sugar,  which  is  found,  whether  saccharine  or  farinaceous 
matter  have  been  present  in  the  food  or  not. 

Besides  the  rather  wide  difference  between  the  composition 
of  the  blood  of  these  veins  and  of  others,  it  must  not  be  for- 
gotten that  in  its  passage  through  every  organ  and  tissue  of 
the  body,  the  blood's  composition  must  be  varying  constantly, 
as  each  part  takes  from  it  or  adds  to  it  such  matter  as  it, 
roughly  speaking,  wishes  either  to  have  or  to  throw  away. 
Thus  the  blood  of  the  renal  vein  has  been  proved  by  experi- 
ment to  contain  less  water  than  does  the  blood  of  the  artery, 
and  doubtless  its  salts  are  diminished  also.  The  blood  in  the 
renal  vein  is  said,  moreover,  by  Bernard  and  Brown-Sequard 
not  to  coagulate. 

This  then  is  an  example  of  the  change  produced  in  the 
blood  by  its  passage  through  a  special  excretory  organ.  But 
all  parts  of  the  body,  bones,  muscles,  nerves,  &c.,  must  act  on 
the  blood  as  it  passes  through  them,  and  leave  in  it  some  mark 


DEVELOPMENT     OF     BLOOD.  81 

of  their  action,  too  slight  though  it  may  be,  at  any  given  mo- 
ment, for  analysis  by  means  now  at  our  disposal. 

On  the  Gases  contained  in  the  Blood. 

The  gases  contained  in  the  blood  are  carbonic  acid,  oxygen, 
and  nitrogen,  100  volumes  of  blood  containing  from  40  to  50 
volumes  of  these  gases  collectively. 

Arterial  blood  contains  relatively  more  oxygen  and  less 
carbonic  acid  than  venous.  But  the  absolute  quantity  of  car- 
bonic acid  is  in  both  kinds  of  blood  greater  than  that  of  the 
oxygen.  The  proportion  of  nitrogen  is  in  both  very  small. 

It  is  most  probable  that  the  carbonic  acid  of  the  blood  is 
partly  in  a  state  of  simple  solution,  and  partly  in  a  state  of 
weak  chemical  combination.  That  portion  of  the  carbonic 
acid  which  is  chemically  combined,  is  contained  partly  in  a 
bicarbonate  of  soda,  and  partly  is  united  with  phosphate  of 
the  same  base.  The  oxygen  is  combined  chemically  with  the 
haemoglobin  of  the  red  corpuscles  (pp.  69  and  77). 

That  the  oxygen  is  absorbed  chiefly  by  the  red  corpuscles 
is  proved  by  the  fact  that  while  blood  is  capable  of  absorbing 
oxygen  in  considerable  quantity,  the  serum  alone  has  little  or 
no  more  power  of  absorbing  this  gas  than  pure  water. 

Development  of  the  Blood. 

In  the  development  of  the  blood  little  more  can  be  traced 
than  the  processes  by  which  the  corpuscles  are  formed. 

The  first  formed  blood-cells  of  the  human  embryo  differ 
much  in  their  general  characters  from  those  which  belong  to 
the  latter  periods  of  intra-uterine,  and  to  all  periods  of  extra- 
uterine  life.  Their  manner  of  origin  differs  also,  and  it  will 
be  well  perhaps  to  consider  this  first. 

In  the  process  of  development  of  the  embryo,  the  plan,  so 
to  speak,  of  the  heart  and  chief  bloodvessels  is  first  laid  out 
in  cells.  Thus  the  heart  is  at  first  but  a  solid  mass  of  cells, 
resembling  those  which  constitute  all  other  parts  of  the  em- 
bryo ;  and  continuous  with  this  are  tracts  of  similar  cells — 
the  rudiments  of  the  chief  bloodvessels. 

The  formation  of  the  first  blood-corpuscles  is  very  simple. 
While  the  outermost  of  the  embryonic  cells,  of  which  the  ru- 
dimentary heart  and  its  attendant  vessels  are  composed,  gradu- 
ally develop  into  the  muscular  and  other  tissues  which  form 
the  walls  of  the  heart  and  bloodvessels,  the  inner  cells  simply 
separate  from  each  other,  and  form  blood-cells ;  some  fluid 
plasma  being  at  the  same  time  secreted.  Thus,  by  the  same 


82  DEVELOPMENT    OF    BLOOD. 

process,  blood  is  formed,  and  the  originally  solid  heart  and 
bloodvessels  are  hollowed  out. 

The  blood-cells  produced  in  this  way,  are  from  about  ^-^ 
to  y-g-ftfl  of  an  inch  in  diameter,  mostly  spherical,  pellucid,  and 
colorless,  with  granular  contents,  and  a  well-marked  nucleus. 
Gradually,  they  acquire  a  red  color,  at  the  same  time  that  the 
nucleus  becomes  more  defined,  and  the  granular  matter  clears 
away.  Mr.  Paget  describes  them  as,  at  this  period,  circular, 
thickly  disk-shaped,  full-colored,  and,  on  an  average,  about 
2~5"0¥  °f  an  incn  m  diameter ;  their  nuclei,  which  are  about 
WOTT  °f  an  incn  m  diameter,  are  central,  circular,  very  little 
prominent  on  the  surfaces  of  the  cell,  and  apparently  slightly 
granular  or  tuberculated. 

Before  the  occurrence,  however,  of  this  change — from  the 
colorless  to  the  colored  state — in  many  instances,  probably, 
during  it,  and  in  many  afterwards,  a  process  of  multiplication 
takes  place  by  division  of  the  nucleus  and  subsequently  of  the 
cell,  into  two,  and  much  more  rarely,  three  or  four  new  cells, 
which  gradually  acquire  the  characters  of  the  original  cell 
from  which  they  sprang.  Fig.  30  (B,  c,  D,  E). 

FIG.  30. 


D  E  ^^^  F 

Development  of  the  first  setof  blood-corpuscles  in  the  mammalian  embryo.  A.  A 
dotted,  nucleated  embryo-cell  in  process  of  conversion  into  a  blood-corpuscle:  the 
nucleus  provided  with  a  nucleolus.  B.  A  similar  cell  with  a  dividing  nucleus ;  at  c, 
the  division  of  the  nucleus  is  complete  ;  at  D,  the  cell  also  is  dividing.  E.  A  blood- 
corpuscle  almost  complete,  but  still  containing  a  few  granules.  F.  Perfect  blood- 
corpuscle. 

When,  in  the  progress  of  embryonic  development,  the  liver 
begins  to  be  formed,  the  multiplication  of  blood-cells  in  the 
whole  mass  of  blood  ceases,  according  to  Kolliker,  and  new 
blood-cells  are  produced  by  this  organ.  Like  those  just  de- 
scribed, they  are  at  first  colorless  and  nucleated,  but  afterwards 
acquire  the  ordinary  blood  tinge,  and  resemble  very  much 
those  of  the  first  set.  Like  them  they  may  also  multiply  by 


DEVELOPMENT    OF    BLOOD;  S3 

division.  In  whichever  way  produced,  however,  whether  from 
the  original  formative  cells  of  the  embryo,  or  by  the  liver,  these 
colored  nucleated  cells  begin  very  early  in  foetal  life  to  be 
mingled  with  colored  non-nucleated  corpuscles  resembling  those 
of  the  adult,  and  about  the  fourth  or  fifth  month  of  embry- 
onic existence  are  completely  replaced  by  them. 

The  manner  of  origin  of  these  perfect  non-nucleated  cor- 
puscles must  be  now  considered. 

I.    Concerning  the  Cells  from  which  they  arise. 

a.  Before  Birth. — It  is  uncertain  whether  they  are  derived 
only  from  the  cells  of  the  lymph,  which,  at  about  the  period 
of  their  appearance,  begins  to  be  poured  into  the  blood  ;  or 
whether  they  are  derived  also  from  the  nucleated  red  cells, 
which  they  replace,  or  also  from  similar  nucleated  cells,  which 
Kolliker  thinks  are  produced   by  the  liver  during  the  whole 
time  of  fcetal  existence. 

b.  After  Birth. — It  is  generally  agreed  that  after  birth  the 
red  corpuscles  are  derived  from  the  smaller  of  the  nucleated 
lymph  or  chyle-corpuscles, — the  white  corpuscles  of  the  blood. 

II.   Concerning  the  Manner  of  their  Development. 

There  is  not  perfect  agreement  among  physiologists  concern- 
ing the  process  by  which  lymph-globules  or  white  corpuscles 
(and  in  the  foetus,  perhaps  the  red  nucleated  cells)  are  trans- 
formed into  red  non-nucleated  blood-cells.  For  while  some 
maintain  that  the  whole  cell  is  changed  into  a  red  one  by  the 
gradual  clearing  up  of  the  contents,  including  the  nucleus,  it 
is  believed  by  Mr.  Wharton  Jones  and  many  others,  that  only 
the  nucleus  becomes  the  red  blood-cell,  by  escaping  from  its 
envelope  and  acquiring  the  ordinary  blood-tint. 

Of  these  two  theories,  that  which  supposes  the  nucleus  of  the 
lymph  or  chyle  globule  to  be  the  germ  of  the  future  red  blood- 
corpuscle  is  the  theory  now  generally  adopted. 

The  development  of  red  blood-cells  from  the  corpuscles  of 
the  lymph  and  chyle  continues  throughout  life,  and  there  is 
no  reason  for  supposing  that  after  birth  they  have  any  other 
origin. 

Without  doubt,  these  little  bodies  have,  like  all  other  parts 
of  the  organism,  a  tolerably  definite  term  of  existence,  and  in 
a  like  manner  die  and  waste  away  when  the  portion  of  work 
allotted  to  them  has  been  performed.  Neither  the  length  of 
their  life,  however,  nor  the  fashion  of  their  decay,  has  been  yet 
clearly  made  out,  and  we  can  only  surmise  that  in  these  things 


84  DEVELOPMENT    OF    BLOOD. 

they  resemble  more  or  less  closely  those  parts  of  the  body 
which  lie  more  plainly  within  our  observation. 

From  what  has  been  said,  it  will  have  appeared  that  when 
the  blood  is  once  formed,  its  growth  and  maintenance  are  ef- 
fected by  the  constant  repetition  of  the  development  of  new 
portions.  In  the  same  proportion  that  the  blood  yields  its 
materials  for  the  maintenance  and  repair  of  the  several  solid 
tissues,  and  for  secretions,  so  are  new  materials  supplied  to  it 
in  the  lymph  and  chyle,  and  by  development  made  like  it. 
The  part  of  the  process  which  relates  to  the  formation  of  new 
corpuscles  has  been  described,  but  it  is  probably  only  a  small 
portion  of  the  whole  process ;  for  the  assimilation  of  the  new 
materials  to  the  blood  must  be  perfect,  in  regard  to  all  those 
immeasurable  minute  particulars  by  which  the  blood  is  adapted 
for  the  nutrition  of  every  tissue,  and  the  maintenance  of  every 
peculiarity  of  each.  How  precise  the  assimilation  must  be  for 
such  an  adaptation,  may  be  conceived  from  some  of  the  cases 
in  which  the  blood  is  altered  by  disease,  and  by  assimilation  is 
maintained  in  its  altered  state.  For  example,  by  the  inser- 
tion of  vaccine  matter,  the  blood  is  for  a  short  time  manifestly 
diseased ;  however  minute  the  portion  of  virus,  it  affects  and 
alters,  in  some  way,  the  whole  of  the  blood.  And  the  alteration 
thus  produced,  inconceivably  slight  as  it  must  be,  is  long  main- 
tained ;  for  even  very  long  after  a  successful  vaccination,  a 
second  insertion  of  the  virus  may  have  no  effect,  the  blood 
being  no  longer  amenable  to  its  influence,  because  the  new 
blood,  formed  after  the  vaccination,  is  made  like  the  blood  as 
altered  by  the  vaccine  virus ;  in  other  words,  the  blood  exactly 
assimilates  to  its  altered  self  the  materials  derived  from  the 
lymph  and  chyle.  In  health  we  cannot  see  the  precision  of 
the  adjustment  of  the  blood  to  the  tissues  ;  but  we  may  imagine 
it  from  the  small  influences  by  which,  as  in  vaccination,  it  is 
disturbed ;  and  we  may  be  sure  that  the  new  blood  is  as  per- 
fectly assimilated  to  the  healthy  standard  as  in  disease  it  is  as- 
similated to  the  most  minutely  altered  standard.1 

How  far  the  assimilation  of  the  blood  is  affected  by  any  for- 
mative power  which  it  may  possess  in  common  with  the  solid 
tissues,  we  know  not.  That  this  possible  formative  power  is, 
however,  if  present,  greatly  ministered  to  and  assisted  by  the 
actions  of  other  parts  there  can  be  no  doubt;  as  1st,  by  the  di- 
gestive and  absorbent  systems,  and  probably  by  the  liver,  and 
all  of  the  so-called  vascular  glands ;  and,  2dly,  by  the  excre- 
tory organs,  which  separate  from  the  blood  refuse  materials, 

1  Corresponding  facts  in  relation  to  the  maintenance  of  the  tissues 
by  assimilation  will  be  mentioned  in  the  chapter  on  NUTRITION. 


USES    OF    THE     BLOOD.  85 

including  in  this  term  not  only  the  waste  substance  of  the 
tissues,  but  also  such  matters  as,  having  been  taken  with  food 
arid  drink,  may  have  been  absorbed  from  the  digestive  canal, 
and  have  been  subsequently  found  unfit  to  remain  in  the  cir- 
culating current.  And,  3dly,  the  precise  constitution  of  the 
blood  is  adjusted  by  the  balance  of  the  nutritive  processes  for 
maintaining  the  several  tissues^so  that  none  of  the  materials 
appropriate  for  the  maintenance  of  any  part  may  remain  in 
excess  in  the  blood.  Each  part,  by  taking  from  the  blood  the 
materials  it  requires  for  its  maintenance,  is,  as  has  been  ob- 
served, in  the  relation  of  an  excretory  organ  to  all  the  rest; 
inasmuch  as  by  abstracting  the  matters  proper  for  its  nutrition, 
it  prevents  excess  of  such  matters  as  effectually  as  if  they  were 
separated  from  the  blood  and  cast  out  altogether  by  the  ex- 
creting organs  specially  present  for  such  a  purpose. 

Uses  of  the  Blood. 

The  purposes  of  the  blood,  thus  developed  and  maintained, 
appear,  in  the  perfect  state,  to  be  these :  1st,  to  be  a  source 
whence  the  various  parts  of  the  body  may  abstract  the  ma- 
terials necessary  for  their  nutrition  and  maintenance ;  and 
whence  the  secreting  organs  may  take  the  materials  for  their 
various  secretions ;  2d,  to  be  a  constantly  replenished  store- 
house of  latent  chemical  force,  which  in  its  expenditure  will 
maintain  the  heat  of  the  body,  or  be  transformed  by  the  living 
tissues,  and  manifested  by  them  in  various  forms  as  vital  power ; 
3d,  to  convey  oxygen  to  the  several  tissues  which  may  need  it, 
either  for  the  discharge  of  their  functions,  or  for  combination 
with  their  refuse  matter ;  4th,  to  bring  from  all  parts  refuse 
matters,  and  convey  them  to  places  whence  they  may  be  dis- 
charged ;  5th,  to  warm  and  moisten  all  parts  of  the  body. 

Uses  of  the  various  Constituents  of  the  Blood. 

Regarding  the  uses  of  the  various  constituents  of  the  blood, 
it  may  be  said  that  the  matter  almost  resolves  itself  into  an 
analysis  of  the  different  parts  of  the  body,  and  of  the  food  and 
drink  which  are  taken  for  their  nutrition,  with  a  subsequent 
consideration  of  how  far  any  given  constituent  of  the  blood 
may  be  supposed  to  be  on  its  way  to  the  living  tissues,  to  be 
incorporated  with  and  nourish  them  ;  or,  having  fulfilled  its 
purpose,  to  be  on  its  way,  in  a  more  or  less  changed  condition, 
to  the  excretory  organs  to  be  cast  out.  It  must  be  remem- 
bered, however,  that  the  blood  contains  also  matters  which 
serve  by  their  combustion  to  produce  heat,  and,  again,  others 
which  possibly  subserve  pnly  a  mechanical,  although  most  im- 


86  USES    OF    THE     BLOOD. 

portant  purpose ;  as,  for  instance,  the  preservation  of  the  due 
specific  gravity  of  the  blood,  or  some  other  quality  by  which 
it  is  enabled  to  maintain  its  proper  relation  to  the  vessels  con- 
taining it,  and  to  the  tissues  through  which  it  passes.  Lastly, 
among  the  constituents  of  the  blood,  are  the  gases,  oxygen,  and 
carbonic  acid,  and  the  substances  specially  adapted  to  carry 
them,  which  can  scarcely  be  §aid  to  take  part  in  the  nutrition 
of  the  body,  but  are  rather  the  means  and  evidence  of  the 
combustion  before  referred  to,  on  which,  to  a  great  extent, 
directly  or  indirectly,  all  vitality  depends. 

Albumen. — The  albumen,  which  exists  in  so  large  a  propor- 
tion among  the  chief  constituents  of  the  blood,  is  without 
doubt  mainly  for  the  nourishment  of  those  textures  which 
contain  it  or  other  compounds  nearly  allied  to  it.  Besides  its 
purpose  in  nutrition,  the  albumen  of  the  liquor  sanguinis  is 
doubtless  of  importance  also  in  the  maintenance  of  those  essen- 
tial physical  properties  of  the  blood  to  which  reference  has 
been  already  made. 

Fibrin. — It  has  been  mentioned  in  a  previous  part  of  this 
chapter,  that  the  idea  of  fibrin  existing  in  the  blood,  as  fibrin, 
is  probably  founded  in  error ;  and  that  it  is  formed,  in  the  act 
of  coagulation,  by  the  union  of  two  substances,  which  before 
existed  separately  (p.  61).  In  considering,  therefore,  the  func- 
tions of  fibrin,  we  may  exclude  the  notion  of  its  existence,  as 
such,  in  the  blood,  in  a  fluid  state,  and  of  its  use  in  the  nutri- 
tion of  certain  special  textures,  and  look  for  the  explanation 
of  its  functions  to  those  circumstances,  whether  of  health  or 
disease,  under  which  it  is  produced.  In  hemorrhage,  for  ex- 
ample, the  formation  of  fibrin  in  the  clotting  of  blood,  is  the 
means  by  which,  at  least  for  a  time,  the  bleeding  is  restrained 
or  stopped ;  and  the  material  which  is  produced  for  the  per- 
manent healing  of  the  injured  part,  contains  a  coagulable  ma- 
terial probably  identical,  or  very  nearly  so,  with  the  fibrin  of 
clotted  blood. 

Fatty  Matters. — The  fatty  matters  of  the  blood  subserve  more 
than  one  purpose.  For  while  they  are  the  means,  at  least  in 
part,  by  which  the  fat  of  the  body,  so  widely  distributed  in  the 
proper  adipose  and  other  textures,  is  replenished,  they  also,  by 
their  union  with  oxygen,  assist  in  maintaining  the  temperature 
of  the  body.  In  certain  secretions  also,  notably  the  milk  and 
bile,  fat  is  an  important  constituent. 

Saline  Matter, — The  uses  of  the-  saline  constituents  of  the 
blood  are,  first,  to  enter  into  the  composition  of  such  textures 
and  secretions  as  naturally  contain  them,  and,  secondly,  to 
assist  in  preserving  the  due  specific  gravity  and  alkalinity  of 
the  blood  and,  perhaps,  also  in  preventing  its  decomposition. 


USES    OF    THE     BLOOD.  87 

The  phosphate  and  carbonate  of  sodium,  besides  maintaining 
the  alkalinity  of  the  blood,  are  said  especially  to  preserve  the 
liquidity  of  its  albumen,  and  to  favor  its  circulation  through 
the  capillaries,  at  the  same  time  that  they  increase  the  absorp- 
tive power  of  the  serum  for  gases.  But  although,  from  the 
constant  presence  of  a  certain  quantity  of  saline  matter  in  the 
blood,  we  may  believe  that  it  has  these  last-mentioned  impor- 
tant functions  in  connection  with  the  blood  itself,  apart  from 
the  nutrition  of  the  body,  yet,  from  the  amount  which  is  daily 
separated  by  the  different  excretory  organs,  and  especially  by 
the  kidneys,  wre  must  also  believe  that  a  considerable  quantity 
simply  passes  through  the  blood,  both  from  the  food  and  from 
the  tissues,  as  a  temporary  and  useless  constituent,  to  be  ex- 
creted when  opportunity  offers. 

Corpuscles. — The  uses  of  the  red  corpuscles  are  probably  not 
yet  fully  known,  but  they  may  be  inferred,  at  least  in  part, 
from  the  composition  and  properties  of  their  contents.  The 
affinity  of  haemoglobin  for  oxygen  has  been  already  mentioned ; 
and  the  main  function  of  the  red  corpuscles  seems  to  be  the 
absorption  of  oxygen  in  the  lungs  by  means  of  this  constitu- 
ent, and  its  conveyance  to  all  parts  of  the  body,  especially  to 
those  tissues,  the  nervous  and  muscular,  the  discharge  of  whose 
functions  depends  in  so  great  a  degree  upon  a  rapid  and  full 
supply  of  this  element.  The  readiness  with  which  haemoglo- 
bin absorbs  oxygen,  and  delivers  it  up  again  to  a  reducing 
agent,  so  well  shown  by  the  experiments  of  Prof.  Stokes,  ad- 
mirably adapts  it  for  this  purpose.  How  far  the  red  corpus- 
cles are  concerned  in  the  nutrition  of  the  tissues  is  quite  un- 
known. 

The  relation  of  the  white  to  the  red  corpuscles  of  the  blood 
has  been  already  considered  (p.  83);  of  the  functions  of  the 
former,  other  than  are  concerned  in  this  relationship,  nothing 
is  positively  known.  Recent  observations  of  the  migration  of 
the  white  corpuscles  from  the  interior  of  the  bloodvessels  into 
the  surrounding  tissues  (see  section,  On  the  Circulation  in  the 
Capillaries)  have,  however,  opened  out  a  large  field  for  inves- 
tigation of  their  probable  functions  in  connection  with  the  nu- 
trition of  the  textures,  in  which,  even  in  health,  they  appear 
to  wander. 


88  THE    CIRCULATION. 


CHAPTER  VI. 

CIRCULATION    OF    THE    BLOOD. 

THE  body  is  divided  into  two  chief  cavities — the  chest  or 
thorax  and  abdomen,  by  a  curved  muscular  partition,  called 
the  diaphragm  (Fig.  31).  The  chest  is  almost  entirely  filled 
by  the  lungs  and  heart ;  the  latter  being  fitted  in,  so  to  speak, 
between  the  two  lungs,  nearer  the  front  than  the  back  of  the 
chest,  and  partly  overlapped  by  them  (Fig.  31).  Each  of 
these  organs  is  contained  in  a  distinct  bag,  called  respectively 
the  right  and  left  pleura  and  the  pericardium,  the  latter  being 
fibrous  in  the  main,  but  lined  on  the  inner  aspect  by  a  smooth 
shining  epithelial  covering,  on  which  can  glide,  with  but  little 
friction,  the  equally  smooth  surface  of  the  heart  enveloped  by 
it.  In  Fig.  31  the  containing  bags  of  pleura  and  pericardium 
are  supposed  to  have  been  removed.  Entering  the  chest  from 
above  is  a  large  and  long  air-tube,  called  the  trachea,  which 
divides  into  two  branches,  one  for  each  lung,  and  through 
which  air  passes  and  repasses  in  respiration.  Springing  from 
the  upper  part  or  base  of  the  heart  may  be  seen  the  large  ves- 
sels, arteries,  and  veins,  which  convey  blood  either  to  or  from 
this  organ. 

In  the  living  body  the  heart  and  lungs  are  in  constant 
rhythmic  movement,  the  result  of  which  is  an  unceasing  stream 
of  air  through  the  trachea  alternately  into  and  out  of  the 
lungs,  and  an  unceasing  stream  of  blood  into  and  out  of  the 
heart. 

It  is  with  this  last  event  that  we  are  concerned  especially  in 
this  chapter, — with  the  means,  that  is  to  say,  by  which  the 
blood  which  at  one  moment  is  forced  out  of  the  heart,  is  in  a 
few  moments  more  returned  to  it,  again  to  depart,  and  again 
pass  through  the  body  in  course  of  what  is  technically  called 
the  circulation.  The  purposes  for  which  this  unceasing  cur- 
rent is  maintained,  are  indicated  in  the  uses  of  the  blood  enu- 
merated in  the  preceding  chapter. 

The  blood  is  conveyed  away  from  the  heart  by  the  arteries, 
and  returned  to  it  by  the  veins;  the  arteries  and  veins  being 
continuous  with  each*  other,  at  one  end  by  means  of  the  heart, 
and  at  the  other  by  a  fine  network  of  vessels  called  the  capil- 
laries. The  blood,  therefore,  in  its  passage  from  the  heart 


THE    CIRCULATION.  89 

passes  first  into  the  arteries,  then  into  the  capillaries,  and 
lastly  into  the  veins,  by  which  it  is  conveyed  back  again  to 
the  heart, — thus  completing  a  revolution,  or  circulation. 

FIG.  31. 


Lnrynx. 
Trachea. 


Aorta.         - 


Pnlmonar. 
Artery. 


Diaphragm.    Heart. 

View  of  heart  and  lungs  in  situ.  The  froct  portion  of  the  chest-wall,  and  the  outer 
or  parietal  layers  of  the  pleurae  and  pericardium,  have  been  removed.  The  lungs  are 
partly  collapsed. 

As  generally  described  there  are  two  circulations  by  which 
all  the  blood  must  pass ;  the  one,  a  shorter  circuit  from  the 
heart  to  the  lungs  and  back  again ;  the  other  and  larger  cir- 
cuit, from  the  heart  to  all  parts  of  the  body  and  back  again ; 
but  more  strictly  speaking,  there  is  only  one  complete  circula- 
tion, which  may  be  diagrammatically  represented  by  a  double 
loop,  as  in  Fig.  32. 

On  reference  to  this  figure  and  noticing  the  direction  of  the 
arrows  which  represent  the  course  of  the  stream  of  blood,  it 
will  be  observed  that  while  there  is  a  smaller  and  a  larger 
circle,  both  of  which  pass  through  the  heart,  yet  that  these  are 
not  distinct,  one  from  the  other,  but  are  formed  really  by  one 
continuous  stream,  the  whole  of  which  must,  at  one  part  of  its 
course,  pass  through  the  lungs.  Subordinate  to  the  two  prin- 
cipal circulations,  the  pulmonary  and  systemic,  as  they  are 


90 


THE    CIRCULATION. 


named,  it  will  be  noticed  also  in  the  same  figure,  that  there  is 
another,  by  which  a  portion  of  the  stream  of  blood  having 
been  diverted  once  into  the  capillaries  of  the  intestinal  canal, 
and  some  other  organs,  and  gathered  up  again  into  a  single 
stream,  is  a  second  time  divided  in  its  passage  through  the 


FIG.  32. 


Diagram  of  the  circulation. 


liver,  before  it  finally  reaches  the  heart  and  completes  a  revo- 
lution. This  subordinate  stream  through  the  liver  is  called 
the  portal  circulation. 

The  principal  force  provided  for  constantly  moving  the 
blood  through  this  course  is  that  of  the  muscular  substance  of 
the  heart ;  other  assistant  forces  are,  (2)  those  of  the  elastic 
walls  of  the  arteries,  (3)  the  pressure  of  the  muscles  among 
which  some  of  the  veins  run,  (4)  the  movements  of  the  walls 
of  the  chest  in  respiration,  and  probably,  to  some  extent,  (5) 


THE     HEART.  91 

the  interchange  of  relations  between  the  blood  and  the  tissues 
which  ensues  in  the  capillary  system  during  the  nutritive  pro- 
cesses. The  right  direction  of  the  blood's  course  is  determined 
and  maintained  by  the  valves  of  the  heart  to  be  immediately 
described  ;  which  valves  open  to  permit  the  movement  of  the 
blood  in  the  course  described,  but  close  when  any  force  tends 
to  move  it  in  the  contrary  direction. 

We  shall  consider  separately  each  member  of  the  system  of 
organs  for  the  circulation  :  and  first — 

The  Heart. 

The  heart  is  a  hollow  muscular  organ,  the  interior  of  which 
is  divided  by  a  partition  in  such  a  manner  as  to  form  two 
chief  chambers  or  cavities — right  and  left.  Each  of  these 
chambers  is  again  subdivided  into  an  upper  and  a  lower  por- 
tion called  respectively  the  auricle  and  ventricle,  which  freely 
communicate  one  with  the  other ;  the  aperture  of  communica- 
tion, however,  being  guarded  by  valvular  curtains,  so  disposed 
as  to  allow  blood  to  pass  freely  from  the  auricle  into  the  ven- 
tricle, but  not  in  the  opposite  direction.  There  are  thus  four 
cavities  altogether  in  the  heart — two  auricles  and  two  ventri- 
cles ;  the  auricle  and  ventricle  of  one  side  being  quite  sepa- 
rate from  those  of  the  other.  The  right  auricle  communicates, 
on  the  one  hand,  with  the  veins  of  the  general  system,  and, 
on  the  other,  with  the  right  ventricle,  while  the  latter  leads 
directly  into  the  pulmonary  artery,  the  orifice  of  which  is 
guarded  by  valves.  The  left  auricle  again  communicates,  on 
the  one  hand,  with  the  pulmonary  veins,  and,  on  the  other, 
with  the  left  ventricle,  while  the  latter  leads  directly  into  the 
aorta — a  large  artery  which  conveys  blood  to  the  general  sys- 
tem, the  orifice  of  which,  like  that  of  the  pulmonary  artery,  is 
guarded  by  valves. 

The  arrangement  of  the  heart's  valves  is  such  that  the  blood 
can  pass  only  in  one  definite  direction,  and  this  is  as  follows 
(Fig.  33):  From  the  right  auricle  the  blood  passes  into  the 
right  ventricle,  and  thence  into  the  pulmonary  artery,  by  which 
it  is  conveyed  to  the  capillaries  of  the  lungs.  From  the  lungs 
the  blood,  which  is  now  purified  and  altered  in  color,  is  ga- 
thered by  the  pulmonary  veins  and  taken  to  the  left  auricle. 
From  the  left  auricle  it  passes  into  the  left  ventricle,  and 
thence  into  the  aorta,  by  which  it  is  distributed  to  the  capil- 
laries of  every  portion  of  the  body.  The  branches  of  the  aorta, 
from  being  distributed  to  the  general  system,  are  called  sys- 
temic arteries  ;  and  from  these  the  blood  passes  into  the  systemic 


92  THE    CIRCULATION. 

capillaries,  where  it  again  becomes  dark  and  impure,  and 
thence  into  the  branches  of  the  systemic  veins,  which,  forming 
by  their  union  two  large  trunks,  called  the  superior  and  in- 
ferior vena  cava,  discharge  their  contents  into  the  right  auricle, 
whence  we  supposed  the  blood  to  start  (Fig.  33). 


FIG.  33. 


Diagram  of  the  circulation  through  the  heart  (after  Dalton).  a,  a.  Vena  cava,  su- 
I  erior  and  inferior,  b.  Right  ventricle,  c.  Pulmonary  artery,  d.  Pulmonary  vein. 
e.  Left  ventricle.  /.  Aorta. 


Structure  of  the  Valves  of  the  Heart. 

It  will  be  well  now  to  consider  the  structure  of  the  valves 
of  the  heart,  and  the  manner  in  which  they  perform  their  func- 
tion of  directing  the  stream  of  blood  in  the  course  which  has 
been  just  described.  The  valve  between  the  right  auricle  and 
ventricle  is  named  tricuspid  (Fig.  34),  because  it  presents  three 
principal  cusps  or  pointed  portions,  and  that  between  the  left 
auricle  and  ventricle  bicuspid  or  mitral,  because  it  has  two  such 
portions  (Fig.  35).  But  in  both  valves  there  is  between  each 
two  principal  portions  a  smaller  one;  so  that  more  properly, 
the  tricuspid  may  be  described  as  consisting  of  six,  and  the 


STRUCTURE    OF     HEARTHS    VALVES.  93 

mitral  of  four,  portions.  Each  portion  is  of  triangular  form, 
its  apex  and  sides  lying  free  in  the  cavity  of  the  ventricle,  and 
its  base,  which  is  continuous  with  the  bases  of  the  neighboring 


FIG.  34. 


The  right  auricle  and  ventricle  opened,  and  a  part  of  their  right  and  anterior  walls 
removed,  so  as  to  show  their  interior. — %.  1,  superior  vena  cava;  2,  inferior  vena 
cava  ;  2',  hepatic  veins  cut  short ;  3,  right  auricle ;  3',  placed  in  the  fossa  ovalis,  below 
which  is  the  Eustachian  valve  ;  3",  is  placed  close  to  the  aperture  of  the  coronary 
vein;  +,  +,  placed  in  the  auriculo-ventricular  groove,  where  a  narrow  portion  of 
the  adjacent  walls  of  the  auricle  and  ventricle  has  been  preserved  ;  4,  4,  cavity  of  the 
right  ventricle,  the  upper  figure  is  immediately  below  the  semilunar  valves;  4', 
large  columna  carnea  or  musculus  papillaris  ;  5,  5',  5",  tricuspid  valve  ;  6,  placed  in 
the  interior  of  the  pulmonary  artery,  a  part  of  the  anterior  wall  of  that  vessel  having 
been  removed,  and  a  narrow  portion  of  it  preserved  at  its  commencement  where  the 
semilunar  valves  are  attached ;  7,  concavity  of  the  aortic  arch  close  to  the  cord  of 
the  ductus  arteriosus ;  8,  ascending  part  or  sinus  of  the  arch  covered  at  its  com- 
mencement by  the  auricular  appendix  and  pulmonary  artery ;  9,  placed  between  the 
innominate  and  left  carotid  arteries  ,  10,  appendix  of  the  left  auricle  ;  11, 11,  the  out- 
side of  the  left  ventricle,  the  lower  figure  near  the  apex.  (From  Quain's  Anat»my.) 


94  THE    CIRCULATION. 

portions,  so  as  to  form  an  annular  membrane  around  the  auric- 
ulo- ventricular  opening,  being  fixed  to  a  tendinous  ring,  which 
encircles  the  orifice  between  the  auricle  and  ventricle,  and 
receives  the  insertions  of  the  muscular  fibres  of  both.  In  each 
principal  portion  of  the  valve  may  be  distinguished  a  middle- 
piece,  extending  from  its  base  to  its  apex,  and  including  about 
half  its  width;  this  piece  is  thicker,  and  much  tougher  and 
tighter  than  the  border-pieces,  which  are  attached  loose  and 
flapping  at  its  sides. 

While  the  bases  of  the  several  portions  of  the  valves  are 
fixed  to  the  tendinous  rings,  their  ventricular  surfaces  and 
borders  are  fastened  by  slender  tendinous  fibres,  the  chorda 
tendinece,  to  the  walls  of  the  ventricles,  the  muscular  fibres  of 
which  project  into  the  ventricular  cavity  in  the  form  of  bun- 
dles or  columns — the  columnce  carnece.  These  columns  are  not 
all  of  them  alike,  for  while  some  of  them  are  attached  along 
their  whole  length  on  one  side,  and  by  their  extremities, 
others  are  attached  only  by  their  extremities  ;  and  a  third  set, 
to  which  the  name  musculi  papillares  has  been  given,  are  at- 
tached to  the  wall  of  the  ventricle  by  one  extremity  only,  the 
other  projecting,  papilla-like,  into  the  cavity  of  the  ventricle 
(5,  Fig.  35),  and  having  attached  to  it  chordce  tendinece.  Of 
the  tendinous  cords,  besides  those  which  pass  from  the  walls 
of  the  ventricle  and  the  musculi  papillares,  to  the  margins  of 
the  valves  both  free  and  attached,  there  are  some  of  especial 
strength,  which  pass  from  the  same  parts  to  the  edges  of  the  mid- 
dle pieces  of  the  several  chief  portions  of  the  valve.  The  ends  of 
these  cords  are  spread  out  in  the  substance  of  the  valve,  giving 
its  middle-piece  its  peculiar  strength  and  toughness  ;  and  from 
the  sides  numerous  other  more  slender  and  branching  cords 
are  given  off,  which  are  attached  all  over  the  ventricular  sur- 
face of  the  adjacent  border-pieces  of  the  principal  portions  of 
the  valves,  as  well  as  to  those  smaller  portions  which  have 
been  mentioned  as  lying  between  each  two  principal  ones. 
Moreover,  the  musculi  papillares  are  so  placed  that  from  the 
summit  of  each  tendinous  cords  may  proceed  to  the  adjacent 
halves  of  two  of  the  principal  divisions,  and  to  one  interme- 
diate or  smaller  division,  of  the  valve. 

It  has  been  already  said  that  while  the  ventricles  communi- 
cate, on  the  one  hand,  with  the  auricles,  they  communicate,  on 
the  other,  with  the  large  arteries  which  convey  the  blood  away 
from  the  heart ;  the  right  ventricle  with  the  pulmonary  artery 
(6,  Fig.  34),  which  conveys  blood  to  the  lungs,  and  the  left 
ventricle  with  the  aorta,  which  distributes  it  to  the  general 
system  (7,  Fig.  35).  And  as  the  auriculo-ventricular  orifice 


STRUCTURE    OF    HEARTHS     VALVES. 


95 


is  guarded  by  valves,  so  are  also  the  mouths  of  the  pulmonary 
artery  and  aorta  (Figs.  34,  35). 


FIG.  35. 


The  left  auricle  and  ventricle  opened  and  a  part  of  their  anterior  and  left  walls 
removed  so  as  to  show  their  interior. — %.  The  pulmonary  artery  has  been  divided 
at  its  commencement  so  as  to  show  the  aorta ;  the  opening  into  the  left  ventricle  has 
been  carried  a  short  distance  into  the  aorta  between  two  of  the  segments  of  the 
semilunar  valves  ;  the  left  part  of  the  auricle  with  its  appendix  has  been  removed. 
The  right  auricle  has  been  thrown  out  of  view.  1,  the  two  right  pulmonary  veins 
cut  short ;  their  openings  are  seen  within  the  auricle  ;  1',  placed  within  the  cavity 
of  the  auricle  on  the  left  side  of  the  septum  and  on  the  part  which  forms  the  re- 
mains of  the  valve  of  the  foramen  ovale,  of  which  the  crescentic  fold  is  seen  towards 
the  left  hand  of  1' ;  2,  a  narrow  portion  of  the  wall  of  the  auricle  and  ventricle  pre- 
served round  the  auriculo-ventricular  orifice;  3,  3',  the  cut  surface  of  the  walls  of 
the  ventricle,  seen  to  become  very  much  thinner  towards  3",  at  the  apex  ;  4,  a  small 
part  of  the  anterior  wall  of  the  left  ventricle  which  has  been  preserved  with  the 


96  THE    CIRCULATION. 

The  valves,  three  in  number,  which  guard  the  orifice  of  each 
of  these  two  arteries,  are  called  the  semilunar  valves.  They 
are  nearly  alike  on  both  sides  of  the  heart ;  but  those  of  the 
aorta  are  altogether  thicker  and  more  strongly  constructed 
than  those  of  the  pulmonary  artery.  Like  the  tricuspid  and 
mitral  valves,  they  are  formed  by  a  duplicature  of  the  lining 
membrane  of  the  heart,  strengthened  by  fibrous  tissue.  Each 
valve  is  of  semilunar  shape,  its  convex  margin  being  attached 
to  a  fibrous  ring  at  the  place  of  junction  of  the  artery  to  the 
ventricle,  and  the  concave  or  nearly  straight  border  being  free 
(Fig.  35).  In  the  centre  of  the  free  edge  of  the  valve,  which 
contains  a  fine  cord  of  fibrous  tissue,  is  a  small  fibrous  nodule, 
the  corpus  Arantii,  and  from  this  and  from  the  attached  bor- 
der, fine  fibres  extend  into  every  part  of  the  mid  substance  of 
the  valve,  except  a  small  lunated  space  just  within  the  free 
edge,  on  each  side  of  the  corpus  Arantii.  Here  the  valve  is 
thinnest,  and  composed  of  little  more  than  the  endocardium. 
Thus  constructed  and  attached,  the  three  semilunar  valves  are 
placed  side  by  side  around  the  arterial  orifice  of  each  ventricle, 
so  as  to  form  three  little  pouches,  which  can  be  thrown  back 
and  flattened  by  the  blood  passing  out  of  the  ventricle,  but 
which  belly  out  immediately  so  as  to  prevent  any  return  (6, 
Fig.  34).  This  will  be  again  referred  to  immediately. 

The  muscular  fibres  of  the  heart,  unlike  those  of  most  in- 
voluntary muscles,  present  a  striated  appearance  under  the 
microscope.  (See  chapter  on  Motion.) 

THE   ACTION   OF   THE   HEART. 

The  heart's  action  in  propelling  the  blood  consists  in  the 
successive  alternate  contractions  and  dilatations  of  the  muscu- 
lar walls  of  its  two  auricles  and  two  ventricles.  The  auricles 
contract  simultaneously;  so  do  the  ventricles;  their  dilatations 
also  are  severally  simultaneous ;  and  the  contractions  of  the 
one  pair  of  cavities  are  synchronous  with  the  dilatations  of  the 
other. 

The  description  of  the  action  of  the  heart  may  best  be  corn- 


principal  anterior  columna  carnea  or  musculus  papillaris  attached  to  it;  5,  5,  mus- 
culi  papillares;  5',  the  left  side  of  the  septum,  between  the  two  ventricles,  within 
the  cavity  of  the  left  ventricle ;  6,  6',  the  mitral  valve ;  7,  placed  in  the  interior  of 
the  aorta  near  its  commencement  and  above  the  three  segments  of  its  semilunar 
valve,  which  are  hanging  loosely  together ;  7',  the  exterior  of  the  great  aortic  sinus; 
8,  the  root  of  the  pulmonary  artery  and  its  semilunar  valves  ;  8',  the  separated  por- 
tion of  the  pulmonary  artery  remaining  attached  to  the  aorta  by  9,  the  cord  of  the 
ductus  arteriosus  ;  10,  the  arteries  rising  from  the  summit  of  the  aortic  arch.  (From 
Quain's  Anatomy.) 


ACTION     OF    THE     HEART.  97 

menced  at  that  period  in  each  action  which  immediately  pre- 
cedes the  beat  of  the  heart  against  the  side  of  the  chest,  and, 
by  a  very  small  interval  more,  precedes  the  pulse  at  the  wrist. 
For  at  this  time  the  whole  heart  is  in  a  passive  state,  the  walls 
of  both  auricles  and  ventricles  are  relaxed,  and  their  cavities 
are  being  dilated.  The  auricles  are  gradually  filling  with 
blood  flowing  into  them  from  the  veins ;  and  a  portion  of  this 
blood  passes  at  once  through  them  into  the  ventricles,  the 
opening  between  the  cavity  of  each  auricle  and  that  of  its  cor- 
respond ing  ventricle  being,  during  all  the  pause,  free  and 
patent.  The  auricles,  however,  receiving  more  blood  than  at 
once  passes  through  them  to  the  ventricles,  become,  near  the 
end  of  the  pause,  fully  distended ;  then,  in  the  end  of  the  pause, 
they  contract  and  empty  their  contents  into  the  ventricles.  The 
contraction  of  the  auricles  is  sudden  and  very  quick ;  it  com- 
mences at  the  entrance  of  the  great  veins  into  them,  and  is 
thence  propagated  towards  the  auriculo- ventricular  opening  ; 
but  the  last  part  which  contracts  is  the  auricular  appendix. 
The  effect  of  this  contraction  of  the  auricles  is  to  propel  nearly 
the  whole  of  their  blood  into  the  ventricles.  The  reflux  of 
blood  into  the  great  veins  is  resisted  not  only  by  the  mass  of 
blood  in  the  veins  and  the  force  with  which  it  streams  into  the 
auricles,  but  also  by  the  simultaneous  contraction  of  the  mus- 
cular coats  with  which  the  large  veins  are  provided  for  some 
distance  before  their  entrance  into  the  auricles ;  a  resistance 
which,  however,  is  not  so  complete  but  that  a  small  quantity 
of  blood  does  regurgitate,  i.  e.,  flow  backwards  into  the  veins, 
at  each  auricular  contraction.  The  effect  of  this  regurgitation 
from  the  right  auricle  is  limited  by  the  valves  at  the  junction 
of  the  subclavian  and  internal  jugular  veins,  beyond  which  the 
blood  cannot  move  backwards ;  and  the  coronary  vein,  or  vein 
which  brings  back  to  the  right  auricle  the  blood  which  has 
circulated  in  the  substance  of  the  heart,  is  preserved  from  it 
by  a  valve  at  its  mouth. 

The  blood  which  is  thus  driven,  by  the  contraction  of  the 
auricles,  into  the  corresponding  ventricles,  being  added  to  that 
which  had  already  flowed  into  them  during  the  heart's  pause, 
is  sufficient  to  complete  the  dilatation  or  diastole  of  the  ven- 
tricles. Thus  distended,  they  immediately  contract :  so  im- 
mediately, indeed,  that  their  contraction,  or  systole,  looks  as 
if  it  were  continuous  with  that  of  the  auricles.  This  has  been 
graphically  described  by  Harvey  in  the  following  passage : 
"  These  two  motions,  one  of  the  ventricles,  another  of  the  au- 
ricles, take  place  consecutively,  but  in  such  a  manner  that 
there  is  a  kind  of  harmony,  or  rhythm,  present  between  them, 
the  two  concurring  in  such  wise  that  but  one  motion  is  appar- 


98  T  H  E    C I R  C  U  L  A  T I O  N. 

ent ;  especially  in  the  warmer-blooded  animals,  in  which  the 
movements  in  question  are  rapid.  Nor  is  this  for  any  other 
reason  than  it  is  in  a  piece  of  machinery,  in  which,  though  one 
wheel  gives  motion  to  another,  yet  all  the  wheels  seem  to  move 
simultaneously ;  or  in  that  mechanical  contrivance  which  is 
adapted  to  fire-arms,  where  the  trigger  being  touched,  down 
comes  the  flint,  strikes  against  the  steel,  elicits  a  spark  which, 
falling  among  the  powder,  it  is  ignited,  upon  which  the  flame 
extends,  enters  the  barrel,  causes  the  explosion,  propels  the 
ball,  and  the  mark  is  attained — all  of  which  incidents  by  reason 
of  the  celerity  with  which  they  happen,  seem  to  take  place  in 
the  twinkling  of  an  eye."  The  ventricles  contract  much  more 
slowly  than  the  auricles,  and  in  their  contraction,  probably 
always  thoroughly  empty  themselves,  differing  in  this  respect 
from  the  auricles,  in  which,  even  after  their  complete  contrac- 
tion, a  small  quantity  of  blood  remains.  The  form  and  position 
of  the  fleshy  columns  on  the  internal  walls  of  the  ventricle  ap- 
pear, indeed,  especially  adapted  to  produce  this  obliteration  of 
their  cavities  during  their  contraction  ;  and  the  completeness 
of  the  closure  may  often  be  observed  on  making  a  transverse 
section  of  a  heart  shortly  after  death,  in  any  case  in  which  the 
contraction  of  the  rigor  mortis  is  very  marked.  In  such  a  case, 
only  a  central  fissure  may  be  discernible  to  the  eye  in  the  place 
of  the  cavity  of  each  ventricle. 

At  the  same  time  that  the  walls  of  the  ventricles  contract, 
the  fleshy  columns,"  and  especially  those  of  them  called  the 
musculi  papillares,  contract  also,  and  assist  in  bringing  the 
margins  of  the  auriculo-ventricular  valves  into  apposition,  so 
that  they  close  the  auriculo-ventricular  openings,  and  prevent 
the  backward  passage  of  the  blood  into  the  auricles  (p.  100). 
The  whole  force  of  the  ventricular  contraction  is  thus  directed 
to  the  propulsion  of  the  blood  through  their  arterial  orifices. 
During  the  time  which  elapses  between  the  end  of  one  con- 
traction of  the  ventricles,  and  the  commencement  of  another, 
the  communication  between  them  and  the  great  arteries — the 
aorta  on  the  left  side,  the  pulmonary  artery  on  the  right — is 
closed  by  the  three  semilunar  valves  situated  at  the  orifice  of 
each  vessel.  But  the  force  with  which  the  current  of  blood  is 
propelled  by  the  contraction  of  the  ventricle  separates  these 
valves  from  contact  with  each  other,  and  presses  them  back 
against  the  sides  of  the  artery,  making  a  free  passage  for  the 
stream  of  blood.  Then,  as  soon  as  the  ventricular  contraction 
ceases,  the  elastic  walls  of  the  distended  artery  recoil,  and  by 
pressing  the  blood  behind  the  valves,  force  them  down  towards 
the  centre  of  the  vessel,  and  spread  them  out  so  as  to  close  the 


FUNCTION     OF    THE     VALVES.  99 

orifice,  and  prevent  any  of  the  blood  flowing  back  into  the 
ventricles  (p.  104). 

As  soon  as  the  auricles  have  completed  their  contraction 
they  begin  again  to  dilate,  and  to  be  refilled  with  blood,  which 
flows  into  them  in  a  steady  stream  through  the  great  venous 
trunks.  They  are  thus  filling  during  all  the  time  in  which  the 
ventricles  are  contracting;  and  the  contraction  of  the  ventricles 
being  ended,  these  also  again  dilate,  and  receive  again  the 
blood  that  flows  into  them  from  the  auricles.  By  the  time 
that  the  ventricles  are  thus  from  one-third  to  two-thirds  full, 
the  auricles  are  distended  ;  these,  then  suddenly  contracting, 
fill  up  the  ventricles,  as  already  described. 

If  we  suppose  a  cardiac  revolution,  which  includes  the  con- 
traction of  the  auricles,  the  contraction  of  the  ventricles,  and 
their  repose,  to  occupy  rather  more  than  a  second,  the  following 
table  will  represent,  in  tenths  of  a  second,  the  time  occupied 
by  the  various  events  we  have  considered. 

Contraction  of  Auricles, .     .     .  1  -f  Repose  of  Auricles,  .     .   10  =  11 
"  Ventricles,    .     .   4  -j-          "         Ventricles,    .     7  =  11 

Repose  (no  contraction  of  either 

auricles  or  ventricles),    .     .     ('»  -f  Contraction    of    either 

auricles  or  ventricles,      5=11 
11 


Action  of  the  Valves  of  the  Heart. 

The  periods  in  which  the  several  valves  of  the  heart  are  in 
action  may  be  connected  with  the  foregoing  table ;  for  the 
auriculo-ventricular  valves  are  closed,  and  the  arterial  valves 
are  open  during  the  whole  time  of  the  ventricular  contraction, 
while,  during  the  dilatation  and  distension  of  the  ventricles  the 
latter  valves  are  shut,  the  former  open.  Each  half  or  side  of 
the  heart,  through  the  action  of  its  valves,  may  be  compared 
with  a  kind  of  forcing-pump,  like  the  common  enema-syringe 
with  two  valves,  of  which  one  admits  the  fluid  on  raising  the 
piston,  but  is  closed  again  when  the  piston  is  forced  down ; 
while  the  other  opens  for  the  escape  of  the  fluid,  but  closes 
when  the  piston  is  raised,  so  as  to  prevent  the  regurgitation  of 
the  fluid  already  forced  through  it.  The  ventricular  dilata- 
tion is  here  represented  by  the  raising  up  of  the  piston ;  the 
valve  thus  admitting  fluid  represents  the  auriculo-veutricular 
valve,  which  is  closed  a^aft)  whenUae"  piston  Js;'  foi;c£d  down, 
i.  e.,  when  the  ventricle  contracts^  and  ,tlye"  ;opier,»  i.  e.,  the 
arterial,  valye^opecs: ,  Tfy<^  diagrams, ,pn^  the  following  page 
illustrate  this  <vef y  wpl J. ; .  "-% " ;  ' ; , ;  - ^  \  0  \ 


100 


THE     C I  R  C  U  L  A  T  I  O  X. 


During  auricular  contraction,  the  force  of  the  blood  pro- 
pelled into  the  ventricle  is  transmitted  in  all  directions,  but 


FIG.  36. 


»r  •       <pi&prp,ms  ef  v^l^ec  of  the. heart  (-after- Diriton). 

being  jn^ufficienttp  jraisie  the  ^milu^ar  sralves,  it  is  expended 
in  distepdjug '^c; veitrlole,  nrd  in  raising  an;!  gradually  clos- 


FUNCTION    OF     THE    VALVES.  101 

ing  the  auriculo-ventricular  valves,  which,  when  the  ventricle 
is  full,  form  a  complete  septum  between  it  and  the  auricle. 
This  elevation  of  the  auriculo-veutricular  valves  is,  no  doubt, 
materially  aided  by  the  action  of  the  elastic  tissue  which  Dr. 
Markham  has  shown  to  exist  so  largely  in  their  structure,  es- 
pecially on  the  auricular  surface.  When  the  ventricle  con- 
tracts, the  edges  of  the  valves  are  maintained  in  apposition  by 
the  simultaneous  contraction  of  the  musculi  papillares,  which 
are  enabled  thus  to  act  by  the  arrangement  of  their  tendinous 
cords  just  mentioned.  In  this  position  the  segments  of  the 
valves  are  held  secure,  even  though  the  form  and  size  of  the 
orifice  and  the  ventricle  may  change  during  the  continued 
contraction ;  for  the  border-pieces  are  held  by  their  mutual 
apposition  and  the  equal  pressure  of  the  blood  on  their  ven- 
tricular surfaces ;  and  the  middle-pieces  are  secure  by  their 
great  strength,  and  by  the  attachment  of  the  tendinous  cords 
along  their  margins,  these  cords  being  always  held  tight  by 
the  contraction  of  the  musculi  papillares.  A  peculiar  advan- 
tage, derived  from  the  projection  of  these  columns  into  the 
cavity  of  the  ventricle,  seems  to  be,  that  they  prevent  the 
valve  from  being  converted  into  the  auricle ;  for,  when  the 
ventricle  contracts,  and  the  parts  of  its  walls  to  which,  through 
the  medium  of  the  columns,  the  tendinous  cords  are  affixed, 
approach  the  auriculo-ventricular  orifices,  there  would  be  a 
tendency  to  slackness  of  the  cords,  and  the  valves  might  be 
everted,  if  it  were  not  that  while  the  wall  of  the  ventricle  is 
drawn  towards  the  orifice,  the  end  of  the  simultaneously  con- 
tracting fleshy  column  is  drawn  away  from  it,  and  the  cords 
are  held  tight. 

What  has  been  said  applies  equally  to  the  auriculo-ven- 
tricular valves  on  both  sides  of  the  heart,  and  of  both  alike 
the  closure  is  generally  complete  every  time  the  ventricles 
contract.  But  in  some  circumstances,  the  closure  of  the  tri- 
cuspid  valve  is  not  complete,  and  a  certain  quantity  of  blood 
is  forced  back  into  the  auricle ;  and,  since  this  may  be  advan- 
tageous, by  preventing  the  overfilling  of  the  vessels  of  the 
lungs,  it  has  been  called  the  safety-valve  action  of  this  valve 
(Hunter,  Wilkinson  King).  The  circumstances  in  which  it 
usually  happens  are  those  in  which  the  vessels  of  the  lung  are 
already  full  enough  when  the  right  ventricle  contracts,  as, 
e.  g.,  in  certain  pulmonary  diseases,  in  very  active  exertion, 
and  in  great  efforts.  In  these  cases,  perhaps,  because  the  right 
ventricle  cannot  contract  quickly  or  completely  enough,  the 
tricuspid  valve  does  not  completely  close,  and  the  regurgitation 
of  blood  may  be  indicated  by  a  pulsation  in  the  jugular  veins 
synchronous  with  that  in  the  carotid  arteries. 


102  THE     CIRCULATION. 

The  arterial  or  semilunar  valves  are,  as  already  said,  brought 
into  action  by  the  pressure  of  the  arterial  blood  forced  back 
towards  the  ventricles,  when  the  elastic  walls  of  the  arteries 
recoil  after  being  dilated  by  the  blood  propelled  into  them  in 
the  previous  contraction  of  the  ventricle.  The  dilatation  of 
the  arteries  is,  in  a  peculiar  manner,  adapted  to  bring  the 
valves  into  action.  The  lower  borders  of  the  semilunar  valves 
are  attached  to  the  inner  surface  of  a  tendinous  ring,  which  is, 
as  it  were,  inlaid,  at  the  orifice  of  the  artery,  between  the  mus- 
cular fibres  of  the  ventricle  and  the  elastic  fibres  of  the  walls 
of  the  artery.  The  tissue  of  this  ring  is  tough,  does  not  admit 
of  extension  under  such  pressure  as  it  is  commonly  exposed  to  ; 
the  valves  are  equally  inexteusile,  being,  as  already  mentioned, 
formed  of  tough,  close-textured,  fibrous  tissue,  with  strong  in- 
terwoven cords,  and  covered  with  endocardium.  Hence,  when 
the  ventricle  propels  blood  through  the  orifice  and  into  the 
canal  of  the  artery,  the  lateral  pressure  which  it  exercises  is 
sufficient  to  dilate  the  walls  of  the  artery,  but  not  enough  to 
stretch  in  an  equal  degree,  if  at  all,  the  unyielding  valves  and 
the  ring  to  which  their  lower  borders  are  attached.  The  effect, 
therefore,  of  each  such  propulsion  of  blood  from  the  ventricle 
is,  that  the  wall  of  the  first  portion  of  the  artery  is  dilated  into 
three  pouches  behind  the  valves,  while  the  free  margins  of  the 
valves,  which  had  previously  lain  in  contact  with  the  inner 
surface  of  the  artery  (as  at  A,  Fig.  37),  are  drawn  inward 
towards  its  centre  (Fig.  37,  B).  Their  positions  may  be  ex- 

FlG.  37. 


Sections  of  aorta,  to  show  the  action  of  the  semilunar  valves.  A  is  intended  to 
show  the  valves,  represented  by  the  dotted  lines,  in  contact  with  the  arterial  walls, 
represented  by  the  continuous  outer  line.  B  (after  Hunter)  shows  the  arterial  wall 
distended  into  three  pouches  (a),  and  drawn  away  from  the  valves,  which  are  straight- 
ened into  the  form  of  an  equilateral  triangle,  as  represented  by  the  dotted  lines. 

plained  by  the  foregoing  diagrams,  in  which  the  continuous 
lines  represent  a  transverse  section  of  the  arterial  walls,  the 


FUNCTION    OF    THE    VALVES.  103 

dotted  ones  the  edges  of  the  valves,  firstly,  when  the  valves 
are  in  contact  with  the  walls  (A),  and,  secondly,  when  the 
walls  being  dilated,  the  valves  are  drawn  away  from  them  (B). 
This  position  of  the  valves  and  arterial  walls  is  retained  so 
long  as  the  ventricle  continues  in  contraction ;  but,  so  soon  as 
it  relaxes,  and  the  dilated  arterial  walls  can  recoil  by  their 
elasticity,  they  press  the  blood  as  well  towards  the  ventricles 
as  onwards  in  the  course  of  the  circulation.  Part  of  the  blood 
thus  pressed  back  lies  in  the  pouches  (a,  Fig.  37,  B)  between 
the  valves  and  the  arterial  walls ;  and  the  valves  are  by  it 
pressed  together  till  their  thin  lunated  margins  meet  in  three 
lines  radiating  from  the  centre  to  the  circumference  of  the 
artery  (7  and  8,  Fig.  38). 

FIG.  38. 


View  of  the  base  of  the  ventricular  part  of  the  heart,  showing  the  relative  position 
of  the  arterial  and  auriculo-ventricular  orifices. — %.  The  muscular  fibres  of  the 
ventricles  are  exposed  by  the  removal  of  the  pericardium,  fat,  bloodvessels,  &c. ;  the 
pulmonary  artery  and  aorta  have  been  removed  by  a  section  made  immediately 
beyond  the  attachment  of  the  semilunar  valves,  and  the  auricles  have  been  removed 
immediately  above  the  auriculo-ventricular  orifices.  The  semilunar  and  auriculo- 
ventricular  valves  are  in  the  nearly  closed  condition.  1,  1,  the  base  of  the  right 
ventricle ;  1',  the  conus  arteriosus ;  2,  2,  the  base  of  the  left  ventricle  ;  3,  3,  the  divided 
wall  of  the  right  auricle  ;  4,  that  of  the  left ;  5,  5',  5",  the  tricuspid  valve  ;  6,  6',  the 
mitral  valve.  In  the  angles  between  these  segments  are  seen  the  smaller  fringes 
frequently  observed ;  7,  the  anterior  part  of  the  pulmonary  artery  ;  8,  placed  upon 
the  posterior  part  of  the  root  of  the  aorta ;  9,.  the  rig'ht,  9',  the  left  coronary  artery. 
(From  Quain's  Anatomy.) 

Mr.  Savory  has  clearly  shown  that  this  pressure  of  the  blood 
is  not  entirely  sustained  by  the  valves  alone,  but  in  part  by 


104 


THE     CIRCULATION. 


the  muscular  substance  of  the  ventricle.  Availing  himself  of 
a  method  of  dissection  hitherto  appar- 
ently overlooked,  namely,  that  of  mak- 
ing vertical  sections  (Fig.  39)  through 
various  parts  of  the  tendinous  rings, 
he  has  been  enabled  to  show  clearly 
that  the  aorta  and  pulmonary  artery, 
expanding  towards  their  termination, 
are  situated  upon  the  outer  edge  of  the 
thick  upper  border  of  the  ventricles, 
and  that  consequently  the  portion  of 
each  semilunar  valve  adjacent  to  the 
vessel  passes  over  and  rests  upon  the 
muscular  substance — being  thus  sup- 
ported, as  it  were,  on  a  kind  of  muscu- 
lar floor  formed  by  the  free  border  of 
vertical  section  through  the  the  ventricle.  The  result  of  this  ar- 
aorta  at  its  junction  with  the  rangement  will  be  that  the  reflux  of 
It r"  I',  s^r  ol  the  blood  will  be  most  efficiently  sus- 
valve,  s.  Section  of  ventricle,  tamed  by  the  ventricular  wall.1 

The  effect  of  the  blood's  pressure  on 

the  valves  is,  as  said,  to  cause  their  margins  to  meet  in  three 
lines  radiating  from  the  centre  to  the  circumference  (7  and  8, 
Fig.  38).  The  contact  of  the  valves  in  this  positton,  and  the 
complete  closure  of  the  arterial  orifice,  are  secured  by  the  pe- 
culiar construction  of  their  borders  before  mentioned.  Among 
the  cords  which  are  interwoven  in  the  substance  of  the  valves, 
are  two  of  greater  strength  and  prominence  than  the  rest ;  of 
which  one  extends  along  the  free  border  of  each  valve,  and 
the  other  forms  a  double  curve  or  festoon  just  below  the  free 
border.  Each  of  these  cords  is  attached  by  its  outer  extremi- 
ties to  the  outer  end  of  the  free  margin  of  its  valve,  and  in  the 
middle  to  the  corpus  Arantii;  they  thus  inclose  a  lunated 
space  from  a  line  to  a  line  and  a  half  in  width,  in  which  space 
the  substance  of  the  valve  is  much  thinner  and  more  pliant 
than  elsewhere.  When  the  valves  are  pressed  down,  all  these 
parts  or  spaces  of  their  surfaces  come  into  contact,  and  the 
closure  of  the  arterial  orifice  is  thus  secured  by  the  apposition 
not  of  the  mere  edges  of  the  valves,  but  of  all  those  thin  luna- 
ted parts  of  each,  which  lie  between  the  free  edges  and  the 
cords  next  below  them.  These  parts  are  firmly  pressed  to- 
gether, and  the  greater  the  pressure  that  falls  on  them,  the 


1  Mr.  Savory's  preparations,  illustrating  this  and  other  points  in 
relation  to  the  structure  and  functions  of  the  valves  of  the  heart,  are 
in  the  museum  of  St.  Bartholomew's  Hospital. 


SOUNDS    OF    THE     HEART.  105 

closer  and  more  secure  is  their  apposition.  The  corpora 
Arantii  meet  at  the  centre  of  the  arterial  orifice  when  the 
valves  are  down,  and  they  probably  assist  in  the  closure  ;  but 
they  are  not  essential  to  it,  for,  not  unfrequently,  they  are 
wanting  in  the  valves  of  the  pulmonary  artery,  which  are 
then  extended  in  larger,  thin,  flapping  margins.  In  valves  of 
this  form,  also,  the  inlaid  cords  are  less  distinct  than  in  those 
with  corpora  Arantii ;  yet  the  closure  by  contact  of  their  sur- 
faces is  not  less  secure. 

Sounds  of  the  Heart. 

When  the  ear  is  placed  over  the  region  of  the  heart,  two 
sounds  may  be  heard  at  every  beat  of  the  heart,  which  follow 
in  quick  succession,  and  are  succeeded  by  a  pause  or  period  of 
silence.  The  first  sound  is  dull  and  prolonged  ;  its  commence- 
ment coincides  with  the  impulse  of  the  heart,  and  just  precedes 
the  pulse  at  the  wrist.  The  second  is  a  shorter  and  sharper 
sound,  with  a  somewhat  flapping  character,  and  follows  close 
after  the  arterial  pulse.  The  period  of  time  occupied  respec- 
tively by  the  two  sounds  taken  together,  and  by  the  pause,  are 
almost  exactly  equal.  The  relative  length  of  time  occupied 
by  each  sound,  as  compared  with  the  other,  is  a  little  uncer- 
tain. The  difference  may  be  best  appreciated  by  considering 
the  different  forces  concerned  in  the  production  of  the  two 
sounds.  In  one  case  there  is  a  strong,  comparatively  slow, 
contraction  of  a  large  mass  of  muscular  fibres,  urging  forward 
a  certain  quantity  of  fluid  against  considerable  resistance ; 
while  in  the  other  it  is  a  strong  but  shorter  and  sharper  recoil 
of  the  elastic  coat  of  the  large  arteries — shorter  because  there 
is  no  resistance  to  the  flapping  back  of  the  semilunar  valves,  as 
there  was  to  their  opening.  The  difference  may  be  also  ex- 
pressed, as  Dr.  C.  J.  B.  Williams  has  remarked,  by  saying  the 
words  lubb — dup. 

The  events  which  correspond,  in  point  of  time,  with  the  first 
sound,  are  the  contraction  of  the  ventricles,  the  first  part  of 
the  dilatation  of  the  auricles,  the  closure  of  the  auriculo-ven- 
tricular  valves,  the  opening  of  the  semilunar  valves,  and  the 
propulsion  of  blood  into  the  arteries.  The  sound  is  succeeded, 
in  about  one-thirtieth  of  a  second,  by  the  pulsation  of  the  facial 
artery,  and  in  about  one-sixth  of  a  second,  by  the  pulsation  of 
the  arteries  at  the  wrist.  The  second  sound,  in  point  of  time, 
immediately  follows  the  cessation  of  the  ventricular  contrac- 
tion, and  corresponds  with  the  closure  of  the  semilunar  valves, 
the  continued  dilatation  of  the  auricles,  the  commencing  dila- 
tation of  the  ventricles,  and  the  opening  of  the  auriculo-ven- 


106  THE    CIRCULATION. 

tricular  valves.  The  pause  immediately  follows  the  second 
sound,  and  corresponds  in  its  first  part  with  the  completed  dis- 
tension of  the  auricles,  and  in  its  second  with  their  contraction, 
and  the  distension  of  the  ventricles,  the  auriculo-ventricular 
valves  being  all  the  time  open,  and  the  arterial  valves  closed. 

The  chief  cause  of  the  first  sound  of  the  heart  appears  to  be 
the  vibration  of  the  auriculo-ventricular  valves,  and  also,  but 
to  a  less  extent,  of  the  ventricular  walls,  and  coats  of  the  aorta 
and  pulmonary  artery,  all  of  which  parts  are  suddenly  put  into 
a  state  of  tension  at  the  moment  of  ventricular  contraction. 

This  view,  long  ago  advanced  by  Dr.  Billing,  is  supported 
by  the  fact  observed  by  Valentin,  that  if  a  portion  of  a  horse's 
intestine,  tied  at  one  end,  be  moderately  filled  with  water, 
without  any  admixture  of  air,  and  have  a  syringe  containing 
water  fitted  to  the  other  end,  the  first  sound  of  the  heart  is 
exactly  imitated  by  forcing  in  more  water,  and  thus  suddenly 
rendering  the  walls  of  the  intestine  more  tense. 

The  cause  of  the  second  sound  is  more  simple  than  that  of 
the  first.  It  is  probably  due  entirely  to  the  sudden  closure  and 
consequent  vibration  of  the  semilunar  valves  when  they  are 
pressed  down  across  the  orifices  of  the  aorta  and  pulmonary 
artery ;  for,  of  the  other  events  which  take  place  during  the 
second  sound,  none  is  calculated  to  produce  sound.  The  in- 
fluence of  the  valves  in  producing  the  sound,  is  illustrated  by 
the  experiment  already  quoted  from  Valentin,  and  from  others 
performed  on  large  animals,  such  as  calves,  in  which  the  results 
could  be  fully  appreciated.  In  these  experiments  two  delicate 
curved  needles  were  inserted,  one  into  the  aorta,  and  another 
into  the  pulmonary  artery,  below  the  line  of  attachment  of  the 
semilunar  valves,  and,  after  being  carried  upwards  about  half 
an  inch,  were  brought  out  again  through  the  coats  of  the  re- 
spective vessels,  so  that  in  each  vessel  one  valve  was  included 
between  the  arterial  walls  and  the  wire.  Upon  applying  the 
stethoscope  to  the  vessels,  after  such  an  operation,  the  second 
sound  had  ceased  to  be  audible.  Disease  of  these  valves,  when 
so  extensive  as  to  interfere  with  their  efficient  action,  also  often 
demonstrates  the  same  fact  by  modifying  or  destroying  the  dis- 
tinctness of  the  second  sound. 

One  reason  for  the  second  sound  being  a  clearer  and  sharper 
one  than  the  first  may  be,  that  the  semilunar  valves  are  not 
covered  in  by  the  thick  layer  of  fibres  composing  the  walls  of 
the  heart  to  such  an  extent  as  are  the  auriculo-ventricular.  It 
might  be  expected  therefore  that  their  vibration  would  be  more 
easily  heard  through  a  stethoscope  applied  to  the  walls  of  the 
chest. 

The  contraction  of  the  auricles  which  takes  place  in  the  end 


IMPULSE    OF    THE    HEART.  107 

of  the  pause  is  inaudible  outside  the  chest,  but  may  be  heard, 
when  the  heart  is  exposed  and  the  stethoscope  placed  on  it,  as 
a  slight  sound  preceding  and  continued  into  the  louder  sound 
of  the  ventricular  contraction. 

The  Impulse  of  the  Heart. — At  the  commencement  of  each 
ventricular  contraction,  the  heart  may  be  felt  to  beat  with  a 
slight  shock  or  impulse  against  the  walls  of  the  chest.  This 
impulse  is  most  evident  in  the  space  between  the  fifth  and  sixth 
ribs,  between  one  and  two  inches  to  the  left  of  the  sternum. 
The  force  of  the  impulse,  and  the  extent  to  which  it  may  be 
perceived  beyond  this  point,  vary  considerably  in  different  in- 
dividuals, and  in  the  same  individuals  under  different  circum- 
stances. It  is  felt  more  distinctly,  and  over  a  larger  extent  of 
surface,  in  emaciated  than  in  fat  and  robust  persons,  and  more 
during  a  forced  expiration  than  in  a  deep  inspiration ;  for,  in  the 
one  case,  the  intervention  of  a  thick  layer  of  fat  or  muscle  be- 
tween the  heart  and  the  surface  of  the  chest,  and  in  the  other  the 
inflation  of  the  portion  of  lung  which  overlaps  the  heart,  pre- 
vents the  impulse  from  being  fully  transmitted  to  the  surface. 
An  excited  action  of  the  heart,  and  especially  a  hypertrophied 
condition  of  the  ventricles,  will  increase  the  impulse,  while  a 
depressed  condition,  or  an  atrophied  state  of  the  ventricular 
walls,  will  diminish  it. 

The  impulse  of  the  heart  is  probably  the  result,  in  part,  of  a 
tilting  forwards  of  the  apex,  so  that  it  is  made  to  strike  against 
the  walls  of  the  chest.  This  tilting  movement  is  thought  to  be 
effected  by  the  contraction  of  the  spiral  muscular  fibres  of  the 
ventricles,  and  especially  of  certain  of  these  fibres  which,  ac- 
cording to  Dr.  Reid,  arise  from  the  base  of  the  ventricular 
septum,  pass  downwards  and  forwards,  forming  part  of  the 
septum,  then  emerge  and  curve  spirally  around  the  apex  and 
adjacent  portion  of  the  heart.  The  whole  extent  of  the  move- 
ment thus  produced  is,  however,  but  slight.  The  condition, 
which,  no  doubt,  contributes  most  to  the  occurrence  and  char- 
acter of  the  impulse  of  the  heart,  is  its  change  of  shape ;  for, 
during  the  contraction  of  the  ventricles,  and  the  consequent 
approximation  of  the  base  towards  the  apex,  the  heart  becomes 
more  globular,  and  bulges  so  much,  that  a  distinct  impulse  is 
felt  when  the  finger  is  placed  over  the  bulging  portion,  either 
at  the  front  of  the  chest,  or  under  the  diaphragm.  The  pro- 
duction of  the  impulse  is,  perhaps,  further  assisted  by  the  ten- 
dency of  the  aorta  to  straighten  itself  and  diminish  its  curva- 
ture when  distended  with  the  blood  impelled  by  the  ventricle ; 
and  by  the  elastic  recoil  of  all  the  parts  about  the  base  of  the 
heart/ which  according  to  the  experiments  of  Kurschner,  are 
stretched  downward  and  backward  by  the  blood  flowing  into 


108  THE    CIRCULATION. 

the  auricles  and  ventricles  during  the  dilatation  of  the  latter, 
but  recover  themselves  when,  at  the  beginning  of  the  contrac- 
tion of  the  ventricles,  the  flow  through  the  auriculo-ventricular 
orifices  is  stopped.  But  these  last-mentioned  conditions  can 
only  be  accessory  in  the  perfect  state  of  things ;  for  the  same 
tilting  movement  of  the  heart  ensues  when  its  apex  is  cut  off, 
and  when,  therefore,  no  tension  or  change  of  form  can  be  pro- 
duced by  the  blood. 

Although  what  we  generally  recognize  .as  the  impulse  of  the 
heart  is  produced  in  the  way  just  mentioned,  the  beat  is  not 
so  simple  a  shock  as  it  may  seem  when  only  felt  by  the  finger. 
By  means  of  an  instrument  called  a  cardiograph,  it  may  be 
shown  to  be  compounded  of  three  or  four  shocks,  of  which  the 
finger  can  only  feel  the  greatest. 

The  cardiograph  is  a  tube,  dilated  at  one  end  into  a  cup  or 
funnel,  either  open-mouthed  or  closed  by  an  elastic  membrane, 
while  at  the  other  it  communicates  with  the  interior  of  a  small 
metal  drum,  one  side  of  which  is  formed  by  an  elastic  mem- 
brane, on  which  rests  a  finely-balanced  lever,  like  that  of  the 
sphygmograph  (Fig.  42). 

When  used,  the  cup  at  one  end  of  the  tube  is  placed  imme- 
diately over  the  part  of  the  chest-wall  at  which  the  apex  of 
the  heart  beats ;  while  the  lever  on  the  drum  is  placed  in  con- 
tact with  a  registering  apparatus.  (See  description  of  sphyg- 
mograph, p.  125.)  When  the  heart  beats,  the  shock  commu- 
nicates a  series  of  impulses  to  the  column  of  air  in  the  now 
closed  tube,  with  the  effect  of  raising  the  elastic  wall  of  the 
drum,  and  of  course  the  lever  which  is  attached  to  it.  A 
tracing  of  the  heart's  impulse  is  thus  obtained  in  the  same 
way  as  that  of  the  pulse,  in  the  arteries  (Figs.  44  and  45). 

The  tracing  shows  that  besides  the  strong  beat  which  alone 
the  finger  recognizes  as  the  impulse  of  the  heart,  and  which  is 
caused  by  the  contraction  of  the  ventricles,  there  are  other 
minor  shocks  which  are  imperceptible  to  the  touch.  The 
latter,  M.  Marey,  by  experiments  on  the  lower  animals,  has 
proved  to  be  the  results,  respectively,  of  the  contraction  of  the 
auricles,  and  of  the  closure  of  the  auriculo-ventricular  and 
seniilunar  valves. 

Frequency  and  Force  of  the  Heart's  Action. 

The  frequency  with  which  the  heart  performs  the  actions 
we  have  described,  may  be  counted  by  the  pulses  at  the  wrist, 
or  in  any  other  artery ;  for  these  correspond  with  the  contrac- 
tions of  the  ventricles. 

The  heart  of  a  healthy  adult  man  in  the  middle  period  of 


ACTION     OF    THE     HEART.  109 

life,  acts  from  seventy  to  seventy-five  times  in  a  minute.  The 
frequency  of  the  heart's  action  gradually  diminishes  from  the 
commencement  to  near  the  end  of  life,  but  is  said  to  rise  again 
somewhat  in  extreme  old  age,  thus  : 

In  the    embryo   the   average   number  of 

pulses  in  a  minute  is  .         .         150 


Just  after  birth. 

During  the  first  year, 

During  the  second  year, 

During  the  third  year, 

About  the  seventh  year, 

About   the   fourteenth   year,   the   average 

number  of  pulses  in  a  minute  is 
In  adult  age,        .... 
In  old  age,  ..... 
In  decrepitude,    .... 


from  140  to  130 
130  to  115 
115  to  100 
100  to    90 
90  to    85 

85  to  80 

80  to  70 

70  to  60 

75  to  65 


In  persons  of  sanguine  temperament,  the  heart  acts  some- 
what more  frequently  than  in  those  of  the  phlegmatic  ;  and  in 
the  female  sex  more  frequently  than  in  the  male. 

After  a  meal  its  action  is  accelerated,  and  still  more  so 
during  bodily  exertion  or  mental  excitement;  it  is  slower 
during  sleep.  The  effect  of  disease  in  producing  temporary 
increase  or  diminution  of  the  heart's  action  is  well  known. 
From  the  observation  of  several  experimenters,  it  appears 
that,  in  the  state  of  health,  the  pulse  is  most  frequent  in  the 
morning,  and  becomes  gradually  slower  as  the  day  advances  : 
and  that  this  diminution  of  frequency  is  both  more  regular 
and  more  rapid  in  the  evening  than  in  the  morning.  It  is 
found,  also,  that  as  a  general  rule,  the  pulse,  especially  in  the 
adult  male,  is  more  frequent  in  the  standing  than  in  the  sitting 
posture,  and  in  the  latter,  than  in  the  recumbent  position  ;  the 
difference  being  greatest  between  the  standing  and  the  sitting 
posture.  The  effect  of  change  of  posture  is  greater  as  the  fre- 
quency of  the  pulse  is  greater,  and,  accordingly,  is  more 
marked  in  the  morning  than  in  the  evening.  Dr.  Guy,  by 
supporting  the  body  in  different  postures,  without  the  aid  of 
muscular  effort  of  the  individual,  has  proved  that  the  increased 
frequency  of  the  pulse  in  the  sitting  and  standing  positions  is 
dependent  upon  the  muscular  exertion  engaged  in  maintaining 
them  ;  the  usual  effect  of  these  postures  on  the  pulse  being 
almost  entirely  prevented  when  the  usually  attendant  muscular 
exertion  was  rendered  unnecessary.  The  effect  of  food,  like 
that  of  change  of  posture,  is  greater  in  the  morning  than  in 
the  evening.  According  to  Parrot,  the  frequency  of  the  pulse 
increases  in  a  corresponding  ratio  with  the  elevation  above  the 
sea  ;  and  Dr.  Frankland  informed  the  author,  that  at  the 

10 


110  THE    CIRCULATION. 

summit  of  Mont  Blanc,  his  pulse  was  about  double  the  ordi- 
nary standard  all  the  time  he  was  there.  After  six  hours' 
perfect  rest  and  sleep  at  the  top,  it  was  120,  on  descending  to 
the  corridor  it  fell  to  108,  at  the  Grands  Mulcts  it  was  88,  at 
Chamounix  56 ;  normally,  his  pulse  is  60. 

In  health,  there  is  observed  a  nearly  uniform  relation  be- 
tween the  frequency  of  the  pulse  and  of  the  respirations ;  the 
proportion  being,  on  an  average,  one  of  the  latter  to  three  or 
four  of  the  former.  The  same  relation  is  generally  main- 
tained in  the  cases  in  which  the  pulse  is  naturally  accelerated, 
as  after  food  or  exercise ;  but  in  disease  this  relation  usually 
ceases  to  exist.  In  many  affections  accompanied  with  in- 
creased frequency  of  the  pulse,  the  respiration  is,  indeed,  also 
accelerated,  yet  the  degree  of  its  acceleration  bears  no  definite 
proportion  to  the  increased  number  of  the  heart's  actions,  and 
in  many  other  cases,  the  pulse  becomes  more  frequent  without 
any  accompanying  increase  in  the  number  of  respirations ;  or, 
the  respiration  alone  may  be  accelerated,  the  number  of  pul- 
sations remaining  stationary,  or  even  falling  below  the  ordi- 
nary standard.  (On  the  whole  of  this  subject,  the  article 
Pulse,  by  Dr.  Guy,  in  the  Cyclopaedia  of  Anatomy  and  Physi- 
ology, may  be  advantageously  consulted.) 

The  force  with  which  the  left  ventricle  of  the  heart  contracts 
is  about  double  that  exerted  by  the  contraction  of  the  right : 
being  equal  (according  to  Valentin)  to  about  -^th  of  the 
weight  of  the  whole  body,  that  of  the  right  being  equal  only 
to  youth  of  the  same.  This  difference  in  the  amount  of  force 
exerted  by  the  contraction  of  the  two  ventricles,  results  from 
the  walls  of  the  left  ventricle  being  about  twice  as  thick  as 
those  of  the  right.  And  the  difference  is  adapted  to  the 
greater  degree  of  resistance  which  the  left  ventricle  has  to 
overcome,  compared  with  that  to  be  overcome  by  the  right ; 
the  former  having  to  propel  blood  through  every  part  of  the 
body,  the  latter  only  through  the  lungs. 

The  force  exercised  by  the  auricles  in  their  contraction  has 
not  been  determined.  Neither  is  it  known  with  what  amount 
of  force  either  the  auricles  or  the  ventricles  dilate ;  but  there  is 
no  evidence  for  the  opinion,  that  in  their  dilatation  they  can 
materially  assist  the  circulation  by  any  such  action  as  that  of 
a  sucking-pump,  or  a  caoutchouc  bag,  in  drawing  blood  into 
their  cavities.  That  the  force  which  the  ventricles  exercise  in 
dilatation  is  very  slight,  has  been  proved  by  Oesterreicher. 
He  removed  the  heart  of  a  frog  from  the  body,  and  laid  upon 
it  a  substance  sufficiently  heavy  to  press  it  flat,  and  yet  so 
small  as  not  to  conceal  the  heart  from  view ;  he  then  observed 
that  during  the  contraction  of  the  heart,  the  weight  was  raised  ; 


RHYTHM    OF    THE     HEART.  Ill 

but  that  during  its  dilatation,  the  heart  remained  flat.  And 
the  same  was  shown  by  Dr.  Clendinning,  who,  applying  the 
points  of  a  pair  of  spring  callipers  to  the  heart  of  a  live  ass, 
found  that  their  points  were  separated  as  often  as  the  heart 
swelled  up  in  the  contraction  of  the  ventricles,  but  approached 
each  other  by  the  force  of  the  spring  when  the  ventricles  di- 
lated. Seeing  how  slight  the  force  exerted  in  the  dilatation  of 
the  ventricles  is,  it  has  been  supposed  that  they  are  only  di- 
lated by  the  pressure  of  the  blood  impelled  from  the  auricles ; 
but  that  both  ventricles  and  auricles  dilate  spontaneously  is 
proved  by  their  continuing  their  successive  contractions  and 
dilatations  when  the  heart  is  removed,  or  even  when  they  are 
separated  from  one  another,  and  when  therefore  no  such  force 
as  the  pressure  of  blood  can  be  exercised  to  dilate  them.  By 
such  spontaneous  dilatation  they  at  least  offer  no  resistance  to 
the  influx  of  blood,  and  save  the  force  which  would  otherwise 
be  required  to  dilate  them. 

The  capacity  of  the  two  ventricles  is  probably  exactly  the 
same.  It  is  difficult  to  determine  with  certainty  how  much 
this  may  be ;  but,  taking  the  mean  of  various  estimates,  it  may 
be  inferred  that  each  ventricle  is  able  to  contain  on  an  aver- 
age, about  three  ounces  of  blood,  the  whole  of  which  is  im- 
pelled into  their  respective  arteries  at  each  contraction.  The 
capacity  of  the  auricles  is  rather  less  than  that  of  the  ven- 
tricles :  the  thickness  of  their  walls  is  considerably  less.  The 
latter  condition  is  adapted  to  the  small  amount  of  force  which 
the  auricles  require  in  order  to  empty  themselves  into  their  ad- 
joining ventricles ;  the  former  to  the  circumstance  of  the  ven- 
tricles being  partly  filled  with  blood  before  the  auricles  con- 
tract. 

Cause  of  the  Rhythmic  Action  of  the  Heart. 

It  has  been  attempted  in  various  ways  to  account  for  the 
existence  and  continuance  of  the  rhythmic  movements  of  the 
heart.  By  some  it  has  been  supposed  that  the  contact  of  blood 
with  the  lining  membrane  of  the  cavities  of  the  heart,  furnishes 
a  stimulus,  in  answer  to  which  the  walls  of  these  cavities  con- 
tract. But  the  fact  that  the  heart,  especially  in  amphibia  and 
fishes,  will  continue  to  contract  and  dilate  regularly  and  in 
rhythmic  order  after  it  is  removed  from  the  body,  completely 
emptied  of  blood,  and  even  placed  in  a  vacuum  where  it  can- 
not receive  the  stimulus  of  the  atmospheric  air,  is  a  proof  that 
even  if  the  contact  of  blood  be  the  ordinary  stimulus  to  the 
heart's  contraction,  it  cannot  alone  be  an  explanation  of  its 
rhythmic  motion. 

The  influence  of  the  mind,  and  of  some  affections  of  the 


112  THE    CIRCULATION. 

brain  and  spinal  cord  upon  the  action  of  the  heart,  proves  that 
it  is  not  altogether,  or  at  all  times,  independent  of  the  cerebro- 
spinal  nervous  system.  Yet  the  numerous  experiments  insti- 
tuted for  the  purpose  of  determining  the  exact  relation  in 
which  the  heart  stands  towards  this  system,  have  failed  to  prove 
that  the  action  is  directly  governed  under  ordinaiy  circum- 
stances by  the  power  of  any  portion  of  the  brain  or  spinal  cord. 
Sudden  destruction  of  either  the  brain  or  spinal  cord  alone,  or 
of  both  together,  produces,  immediately,  a  temporary  interrup- 
tion or  cessation  of  the  heart's  action :  but  this  appears  to  be 
only  an  effect  of  the  shock  of  so  severe  an  injury ;  for,  in  some 
such  cases,  the  movements  of  the  heart  are  subsequently  re- 
sumed, and  if  artificial  respiration  be  kept  up,  may  continue 
for  a  considerable  time ;  and  may  then  again  be  arrested  by 
a  violent  shock  applied  through  an  injury  of  the  stomach. 
While,  therefore,  we  must  admit  an  indirect  or  occasional  in- 
fluence exercised  by,  or  through,  the  brain  and  spinal  cord 
upon  the  movements  of  the  heart,  and  may  believe  this  in- 
fluence to  be  the  greater  the  more  highly  the  several  organs 
are  developed,  yet  it  is  clear  that  we  cannot  ascribe  the  regu- 
lar determination  and  direction  of  the  movements  to  these 
nervous  centres. 

The  persistence  of  the  movements  of  the  heart  in  their  regu- 
lar rhythmic  order,  after  its  removal  from  the  body,  and  their 
capability  of  being  then  re-excited  by  an  ordinary  stimulus 
after  they  have  ceased,  prove  that  the  cause  of  these  move- 
ments must  be  resident  within  the  heart  itself.  And  it  seems 
probable,  from  the  experiments  and  observations  of  various 
observers,  that  it  is  connected  with  the  existence  of  numerous 
minute  ganglia  of  the  sympathetic  nervous  system,  which,  with 
connecting  nerve-fibres,  are  distributed  through  the  substance 
of  the  heart.  These  ganglia  appear  to  act  as  so  many  centres 
or  organs  for  the  production  of  motor  impulses ;  while  the  con- 
necting nerve-fibres  unite  them  into  one  system,  and  enable 
them  to  act  in  concert  and  direct  their  impulses  so  as  to  excite 
in  regular  series  the  successive  contractions  of  the  several 
muscles  of  the  heart.  The  mode  in  which  ganglia  thus  act  as 
centres  and  co-ordinators  of  nervous  power  will  be  described  in 
the  chapter  on  the  NERVOUS  SYSTEM  ;  and  it  will  appear  prob- 
able that  the  chief  peculiarity  of  the  heart,  in  this  respect,  is 
due  to  the  number  of  its  ganglia,  and  the  apparently  equal 
power  which  they  all  exercise  ;  so  that  there  is  no  one  part  of 
the  heart  whose  action,  more  than  another's,  determines  the 
actions  of  the  rest.  Thus,  if  the  heart  of  a  reptile  be  bisected, 
the  rhythmic,  successive  actions  of  auricle  and  ventricle  will 
go  on  in  both  halves :  we  therefore  cannot  say  that  the  action 


RHYTHM     OF    THE     HEART.  113 

of  the  right  side  determines  or  regulates  that  of  the  left,  or 
vice  versd;  and  we  must  suppose  that  when  they  act  together 
in  the  perfect  heart,  it  is  because  they  are  both,  as  it  were,  set 
to  the  same  time.  Neither  can  we  say  that  the  auricles  deter- 
mine the  action  of  the  ventricles ;  for,  if  they  are  separated, 
they  will  both  contract  and  dilate  in  regular,  though  not  nec- 
essarily similar,  succession.  A  fact  pointed  out  by  Mr.  Mai- 
den shows  how  the  several  portions  of  each  cavity  are  similarly 
adjusted  to  act  alike,  yet  independently  of  each  other.  If  a 
point  of  the  surface  of  the  ventricle  of  a  turtle's  or  frog's  heart 
be  irritated,  it  will  immediately  contract,  and  very  quickly 
afterwards  all  the  rest  of  the  ventricle  will  contract ;  but,  at 
the  close  of  this  general  contraction,  the  part  that  was  irritated 
and  contracted  first,  is  slightly  distended  or  pouched  out,  show- 
ing that  it  was  adjusted  to  contract  in,  and  for  only,  a  certain 
time,  and  that  therefore  as  it  began  to  contract  first,  so  it  began 
to  dilate  first. 

The  best  interpretation,  perhaps,  yet  given  of  it,  and  of 
rhythmic  processes  in  general,  is  that  by  Mr.  Taget,  who  re- 
gards them  as  dependent  on  rhythmic  nutrition,  i.  e.,  on  a 
method  of  nutrition  in  which  the  acting  parts  are  gradually 
raised,  with  time-regulated  progress,  to  a  certain  state  of  in- 
stability of  composition,  which  then  issues  in  the  discharge  of 
their  functions,  e.  g.,  of  nerve-force  in  the  case  of  the  cardiac 
ganglia,  by  which  force  the  muscular  walls  are  excited  to  con- 
traction. According  to  this  view,  there  is  in  the  nervous 
ganglia  of  the  heart,  and  in  all  parts  originating  rhythmic  pro- 
cesses, the  same  alternation  of  periods  of  action  with  periods  of 
repose,  during  which  the  waste  in  the  structure  is  repaired,  as 
is  observed  in  most  of,  if  not  all,  the  organic  phenomena  of 
life.  All  organic  processes  seem  to  be  regulated  with  exact 
observance  of  time;  and  rhythmic  nutrition  and  action,  as  ex- 
hibited in  the  action  of  the  heart,  are  but  well  marked  ex- 
amples of  such  chrouometric  arrangement. 

We  may  conclude,  then,  that  the  nervous  ganglia  in  the 
heart's  substance  are  the  immediate  regulators  of  the  heart's 
action,  but  that  they  are  themselves  liable  to  influences  con- 
veyed from  without,  through  branches  of  the  pueumogastric 
and  sympathetic  nerves. 

The  pneumogastric  nerves  are  the  media  of  an  inhibitory  or 
restraining  influence  over  the  action  of  the  heart ;  for  when  by 
section  their  influence  is  withdrawn,  the  pulsations  of  the 
organ  are  increased  in  frequency  and  strength  ;  while  an  oppo- 
site effect  is  produced  by  stimulating  them, — the  transmission 
of  an  electric  current  of  even  moderate  strength  diminishing 
the  pulsations,  or  stopping  them  altogether.  Stimulation  of 


114  THE    CIRCULATION. 

the  sympathetic  nerves,  on  the  other  hand,  accelerates  and 
strengthens  the  heart's  action. 

Various  theories  have  been  proposed  to  account  for  these 
peculiar  results,  but  none  of  them  are  very  satisfactory,  and  it 
is  probable  that  many  more  facts  must  be  discovered  before 
any  theory  on  the  subject  can  be  permanently  maintained. 

The  connection  of  the  action  of  the  heart  with  the  other 
organs,  and  the  influences  to  which  it  is  subject  through  them, 
are  explicable  from  the  connection  of  its  nervous  system  with 
the  other  ganglia  of  the  sympathetic,  and  with  the  brain  and 
spinal  cord  through,  chiefly,  the  pneumogastric  nerves.  But 
this  influence  is  proved  in  a  much  more  striking  manner  by 
the  phenomena  of  disease  than  by  any  experimental  or  other 
physiological  observations.  The  influence  of  a  shock  in  arrest- 
ing or  modifying  the  action  of  the  heart, — its  very  slow  action 
after  compression  of  the  brain,  or  injury  to  the  cervical  por- 
tion of  the  spinal  cord, — its  irregularities  and  palpitations  in 
dyspepsia  and  hysteria, — are  better  evidence  for  the  connection 
of  the  heart  with  the  other  organs  through  the  nervous  sys- 
tem, than  are  any  results  obtained  by  experiments. 

Effects  of  the  Heart's  Action. 

That  the  contractions  of  the  heart  supply  alone  a  sufficient 
force  for  the  circulation  of  the  blood,  appears  to  be  established 
by  the  results  of  several  experiments,  of  which  the  following 
is  one  of  the  most  conclusive :  Dr.  Sharpey  injected  bullock's 
blood  into  the  thoracic  aorta  of  a  dog  recently  killed,  after 
tying  the  abdominal  aorta  above  the  renal  arteries,  and  found 
that,  with  a  force  just  equal  to  that  by  which  the  ventricle 
commonly  impels  the  blood  in  the  dog,  the  blood  which  he  in- 
jected into  the  aorta  passed  iu  a  free  stream  out  of  the  trunk 
of  the  vena  cava  inferior.  It  thus  traversed  both  the  systemic 
and  hepatic  capillaries ;  and  when  the  aorta  was  not  tied 
above  the  renals,  blood  injected  under  the  same  pressure 
flowed  freely  through  the  vessels  of  the  lower  extremities.  A 
pressure  equal  to  that  of  one  and  a  half  or  two  inches  of  mer- 
cury was,  in  the  same  way,  found  sufficient  to  propel  blood 
through  the  vessels  of  the  lungs. 

But  although  it  is  probably  true  that  the  heart's  action 
alone  is  sufficient  to  insure  the  circulation,  yet  there  exist 
several  other  forces  which  are,  as  it  were,  supplementary  to 
the  action  of  the  heart,  and  assist  it  in  maintaining  the  circu- 
lation. The  principal  of  these  supplemental  forces  have  been 
already  alluded  to,  and  will  now  be  more  fully  pointed  out. 


STRUCTURE    OF    ARTERIES.  115 


THE   ARTERIES. 

The  walls  of  the  arteries  are  composed  of  three  principal 
coats,  termed  the  external  or  tunica  adventitia,  the  middle,  and 
the  internal,  while  the  latter  is  lined  within  by  a  single  layer 
of  tessellated  epithelium. 

The  external  coat  or  tunica  adventitia,  the  strongest  and 
toughest  part  of  the  wall  of  the  artery,  is  formed  of  areolar 
tissue,  with  which  is  mingled  throughout  a  network  of  elastic 
fibres.  At  the  inner  part  of  this  outer  coat  the  elastic  network 
forms  in  most  arteries  so  distinct  a  layer  as  to  be  sometimes 
called  the  external  elastic  coat. 

The  middle  coat  is  composed  of  both  muscular  and  elastic 
fibres. 

The  former,  which  are  of  the  pale  or  unstriped  variety  (see 
chapter  on  Motion),  are  arranged  for  the  most  part  trans- 
versely to  the  long  axis  of  the  artery;  while  the  elastic  ele- 
ment, taking  also  a  transverse  direction,  is  disposed  in  the 
form  of  closely  interwoven  and  branching  fibres,  which  inter- 
sect in  all  parts  the  layers  of  muscular  fibre.  In  arteries  of 
various  size  there  is  a  difference  in  the  proportion  of  the  mus- 
cular and  elastic  element,  elastic  tissue  preponderating  in  the 
largest  arteries,  while  this  condition  is  reversed  in  those  of 
medium  and  small  size. 

The  internal  arterial  coat  is  formed  by  layers  of  elastic  tis- 
sue, consisting  in  part  of  coarse  longitudinal  branching  fibres, 
and  in  part  of  a  very  thin  and  brittle  membrane  which  pos- 
sesses little  elasticity,  and  is  thrown  into  folds  or  wrinkles 
when  the  artery  contracts.  This  latter  membrane,  the  striated 
or  fenestrated  coat  of  Henle,  is  peculiar  in  its  tendency  to  curl 
up,  when  peeled  off  from  the  artery,  and  in  the  perforated  and 
streaked  appearance  which  it  presents  under  the  microscope. 
Its  inner  surface  is  lined  with  a  delicate  layer  of  epithelium, 
composed  of  thin  squamous  elongated  cells,  which  make  it 
smooth  and  polished,  and  furnish  a  nearly  impermeable  sur- 
face, along  which  the  blood  may  flow  with  the  smallest  possible 
amount  of  resistance  from  friction. 

The  walls  of  the  arteries,  with  the  possible  exception  of  the 
epithelial  lining  and  the  layers  of  the  internal  coat  immedi- 
ately outside  it,  are  not  nourished  by  the  blood  which  they 
convey,  but  are,  like  other  parts  of  the  body,  supplied  with 
little  arteries,  ending  in  capillaries  and  veins,  which,  branching 
throughout  the  external  coat,  extend  for  some  distance  into 
the  middle,  but  do  not  reach  the  internal  coat.  These  nutrient 
vessels  are  called  vasa  vasorum.  Nerve-fibres  are  also  supplied 
to  the  walls  of  the  arteries. 


116 


THE     CIRCULATION. 


The  function  of  the  arteries  is  to  convey  blood  from  the 
heart  to  all  parts  of  the  body,  and  each  tissue  which  enters 
into  the  construction  of  an  artery  has  a  special  purpose  to 
serve  in  this  distribution. 

(1.)  The  external  coat  forms  a  strong  and  tough  investment, 


FIG.  40. 


FIG.  41. 


FIG.  40. — Muscular  fibre-cells  from  human  arteries,  magnified  350  diameters 
(Kolliker).  a,  natural  state  ;  ft,  treated  with  acetic  acid. 

FIG.  41.— Portion  of  fenestrated  membrane  from  the  crural  artery,  magnified  200 
diameters,  a,  b,  c,  perforations  (from  Henle). 

which,  though  capable  of  extension,  appears  principally  de- 
signed to  strengthen  the  arteries  and  to  guard  against  their 
excessive  distension  from  the  force  of  the  heart's  action.  In 
it,  too,  the  little  vasa  vasorum  find  a  suitable  tissue  in  which  to 
subdivide  for  the  supply  of  the  arterial  coats. 

(2.)  The  purpose  of  the  elastic  tissue,  which  enters  so  largely 
into  the  formation  of  all  the  coats  of  the  arteries,  is,  1st.  To 
guard  the  arteries  from  the  suddenly  exerted  pressure  to  which 
they  are  subjected  at  eac-h  contraction  of  the  ventricles.  In 
every  such  contraction,  the  contents  of  the  ventricles  are  forced 
into  the  arteries  more  quickly  than  they  can  be  discharged 
into  and  through  the  capillaries.  The  blood  therefore  being, 
for  an  instant,  resisted  in  its  onward  course,  a  part  of  the  force 
with  which  it  was  impelled  is  directed  against  the  sides  of  the 
arteries;  under  this  force,  which  might  burst  a  brittle  tube, 
their  elastic  walls  dilate,  stretching  enough  to  receive  the 
blood,  and  as  they  stretch,  becoming  more  tense  and  more 
resisting.  Thus,  by  yielding,  they,  as  it  were,  break  the  shock 


ELASTICITY     OF     ARTERIES.  117 

of  the  force  impelling  the  blood,  and  exhaust  it  before  they 
are  in  danger  of  bursting,  through  being  overstretched.  Elas- 
ticity is  thus  advantageous  in  all  arteries,  but  chiefly  so  in  the 
aorta  and  its  large  branches,  which  are  provided,  as  already 
said,  with  a  large  proportional  quantity  of  elastic  tissue,  in 
adaptation  to  the  great  force  of  the  left  ventricle,  which  falls 
first  on  them,  and  to  the  increased  pressure  of  the  arterial 
blood  in  violent  expiratory  efforts. 

On  the  subsidence  of  the  pressure,  when  the  ventricles  cease 
contracting,  the  arteries  are  able,  by  the  same  elasticity,  to 
resume  their  former  calibre;  and  in  thus  doing,  they  manifest, 
2d,  the  chief  purpose  of  their  elasticity,  that,  namely,  of  equal- 
izing the  current  of  the  blood  by  maintaining  pressure  on  the 
blood  in  the  arteries  during  the  periods  at  which  the  ventricles 
are  at  rest  or  dilating.  If  some  such  method  as  this  had  not 
been  adopted — if,  for  example,  the  arteries  had  been  rigid 
tubes,  the  blood,  instead  of  flowing  as  it  does,  in  a  constant 
stream,  would  have  been  propelled  through  the  arterial  system 
in  a  series  of  jerks  corresponding  to  the  ventricular  contrac- 
tions, with  intervals  of  almost  complete  rest  during  the  inaction 
of  the  ventricles.  But  in  the  actual  condition  of  the  arteries, 
the  force  of  the  successive  contractions  of  the  ventricles  is  ex- 
pended partly  in  the  direct  propulsion  of  the  blood,  and  partly 
in  the  dilatation  of  the  elastic  arteries;  and  in  the  intervals 
between  the  contractions  of  the  ventricles,  the  force  of  the  re- 
coiling and  contracting  arteries  is  employed  in  continuing  the 
same  direct  propulsion.  Of  course,  the  pressure  exercised  by 
the  recoiling  arteries  is  equally  diffused  in  every  direction 
through  the  blood,  and  the  blood  would  tend  to  move  back- 
wards as  well  as  onwards,  but  that  all  movement  backwards 
is  prevented  by  the  closure  of  the  semilunar  arterial  valves, 
which  takes  place  at  the  very  commencement  of  the  recoil  of 
the  arterial  walls. 

By  this  exercise  of  the  elasticity  of  the  arteries,  all  the  force 
of  the  ventricles  is  made  advantageous  to  the  circulation ;  for 
that  part  of  their  force  which  is  expended  in  dilating  the 
arteries,  is  restored  in  full,  according  to  that  law  of  action  of 
elastic  bodies,  by  which  they  return  to  the  state  of  rest  with  a 
force  equal  to  that  by  which  they  were  disturbed  therefrom. 
There  is  thus  no  loss  of  force ;  but  neither  is  there  any  gain, 
for  the  elastic  walls  of  the  artery  cannot  originate  any  force 
for  the  propulsion  of  the  blood — they  only  restore  that  which 
they  received  from  the  ventricles;  they  would  not  contract 
had  they  not  first  been  dilated,  any  more  than  a  spiral  spring 
would  shorten  itself  unless  it  were  first  elongated.  The  advan- 
tage of  elasticity  in  this  respect  is,  therefore,  not  that  it  in- 


118  THE     CIRCULATION. 

creases,  but  that  it  equalizes  or  diffuses  the  force  derived  from 
the  periodic  contractions  of  the  ventricles.  The  force  with 
which  the  arteries  are  dilated  every  time  the  ventricles  con- 
tract, might  be  said  to  be  received  by  them  in  store,  to  be  all 
given  out  again  in  the  next  succeeding  period  of  dilatation  of 
the  ventricles.  It  is  by  this  equalizing  influence  of  the  suc- 
cessive branches  of  every  artery  that,  at  length,  the  intermit- 
tent accelerations  produced  in  the  arterial  current  by  the  action 
of  the  heart,  cease  to  be  observable,  and  the  jetting  stream  is 
converted  into  the  continuous  and  equable  movement  of  the 
blood  which  we  see  in  the  capillaries  and  veins. 

In  the  production  of  a  continuous  stream  of  blood  in  the 
smaller  arteries  and  capillaries,  the  resistance  which  is  offered 
to  the  blood -stream  in  the  capillaries  (p.  136),  is  a  necessary 
agent.  Were  there  no  greater  obstacle  to  the  escape  of  blood 
from  the  arteries  than  exists  to  its  entrance  into  them  from  the 
heart,  the  stream  would  be  intermittent,  notwithstanding  the 
elasticity  of  the  walls  of  the  arteries. 

It  is  the  resistance  which  the  left  ventricle  meets  with  in 
forcing  blood  into  the  arteries  that  causes  part  of  the  force  of 
its  contraction  to  be  expended  in  dilating  them,  or,  as  before 
remarked,  in  laying  up  in  them  a  power  which  will  act  in  the 
intervals  of  the  ventricle's  contraction. 

(3.)  By  means  of  the  elastic  tissue  in  their  walls  (and  of 
the  muscular  tissue  also),  the  arteries  are  enabled  to  dilate  and 
contract  readily  in  correspondence  with  any  temporary  increase 
or  diminution  of  the  total  quantity  of  blood  in  the  body ;  and 
within  a  certain  range  of  diminution  of  the  quantity,  still  to 
exercise  due  pressure  on  their  contents. 

The  elastic  coat,  however,  not  only  assists  in  restoring  the 
normal  calibre  of  an  artery  after  temporary  dilatation,  but 
also  (4),  may  assist  in  restoring  it  after  diminution  of  the  cali- 
brev  whether  this  be  caused  by  a  temporary  contraction  of  the 
muscular  coat,  or  the  application  of  a  compressing  force  from 
without.  This  action  of  the  elastic  tissue  in  arteries,  is  well 
shown  in  arteries  which  contract  after  death,  but  regain  their 
average  patency  on  the  cessation  of  post-mortem  rigidity  (p. 
119).  (5.)  By  means  of  their  elastic  coat  the  arteries  are 
enabled  to  adapt  themselves  to  the  different  movements  of  the 
several  parts  of  the  body. 

We  have  already  referred  to  the  fact  that  the  middle  coat 
of  the  arteries  is  composed  of  unstriped  muscular  fibres,  mingled 
with  fine  elastic  filaments.  The  evidence  for  the  muscular 
contractility  of  arteries  may,  however,  be  given  briefly  for  the 
sake  of  the  physiological  facts  on  which  it  hinges. 

^1.)  When  a  small  artery  in  the  living  subject  is  exposed 


CONTRACTILITY    OF    ARTERIES.  119 

to  the  air  or  cold,  it  gradually  but  manifestly  contracts.  Hun- 
ter observed  that  the  posterior  tibial  artery  of  a  dog  when 
laid  bare,  became  in  a  short  time  so  much  contracted  as  almost 
to  prevent  the  transmission  of  blood  ;  and  the  observation  has 
been  often  and  variously  confirmed.  Simple  elasticity  could 
not  effect  this  ;  for  after  death,  when  the  vital  muscular  power 
has  ceased,  and  the  mechanical  elastic  one  alone  operates,  the 
contracted  artery  dilates  again. 

(2.)  When  aii  artery  is  cut  across,  its  divided  ends  contract, 
and  the  orifices  may  be  completely  closed.  The  rapidity  and 
completeness  of  this  contraction  vary  in  different  animals ; 
they  are  generally  greater  in  young  than  in  old  animals ;  and 
less,  apparently,  in  man  than  in  animals.  In  part  this  con- 
traction is  due  to  elasticity,  but  in  part,  no  doubt,  to  muscular 
action  ;  for  it  is  generally  increased  by  the  application  of  cold, 
or  of  any  simple  stimulating  substances,  or  by  mechanically 
irritating  the  cut  ends  of  the  artery,  as  by  picking  or  twisting 
them.  Such  irritation  would  not  be  followed  by  these  effects, 
if  the  arteries  had  no  other  power  of  contracting  than  that 
depending  upon  elasticity. 

(3.)  The  contractile  property  of  arteries  continues  many 
hours  after  death,  and  thus  affords  an  opportunity  of  distin- 
guishing it  from  elasticity.  When  a  portion  of  an  artery,  the 
splenic,  for  example,  of  a  recently  killed  animal,  is  exposed, 
it  gradually  contracts,  and  its  canal  may  be  thus  completely 
closed  :  in  this  contracted  state  it  remains  for  a  time,  varying 
from  a  few  hours  to  two  days :  then  it  dilates  again,  and  per- 
manently retains  the  same  size.  If,  while  contracted,  the  ar- 
tery be  forcibly  distended,  its  contractility  is  destroyed,  and 
it  holds  a  middle  or  natural  size. 

This  persistence  of  the  contractile  property  after  death  was 
well  shown  in  an  observation  of  Hunter,  which  may  be  men- 
tioned as  proving,  also,  the  greater  degree  of  contractility  pos- 
sessed by  the  smaller  than  by  the  larger  arteries.  Having 
injected  the  uterus  of  a  cow,  which  had  been  removed  from 
the  animal  upwards  of  twenty-four  hours,  he  found,  after  the 
lapse  of  another  day,  that  the  larger  vessels  had  become  much 
more  turgid  than  when  he  injected  them,  and  that  the  smaller 
arteries  had  contracted  so  as  to  force  the  injection  back  into 
the  larger  ones. 

The  results  of  an  experiment  which  Hunter  made  with  the 
vessels  of  an  umbilical  cord  prove  still  more  strikingly  the 
long  continuance  of  the  contractile  power  of  arteries  after 
death.  In  a  woman  delivered  on  a  Thursday  afternoon,  the 
umbilical  cord  was  separated  from  the  foetus,  having  been  first 
tied  in  two  places,  and  then  cut  between,  so  that  the  blood 


120  THE    CIRCULATION. 

contained  in  the  cord  and  placenta  was  confined  in  them.  On 
the  following  morning,  Hunter  tied  a  string  round  the  cord, 
about  an  inch  below  the  other  ligature,  that  the  blood  might 
still  be  confined  in  the  placenta  and  remaining  cord.  Having 
cut  off  this  piece,  and  allowed  all  the  blood  to  escape  from  its 
vessels,  he  attentively  observed  to  what  size  the  ends  of  the 
cut  arteries  were  brought  by  the  elasticity  of  their  coats,  and 
then  laid  aside  the  piece  of  cord  to  see  the  influence  of  the 
contractile  power  of  its  vessels.  On  Saturday  morning,  the 
day  after,  the  mouths  of  the  arteries  were  completely  closed 
up.  He  repeated  the  experiment  the  same  day  with  another 
portion  of  the  same  cord,  and  on  the  following  morning  found 
the  results  to  be  precisely  similar.  On  Sunday,  he  performed 
the  experiment  the  third  time,  but  the  artery  then  seemed  to 
have  lost  its  contractility,  for  on  Monday  morning,  the  mouths 
of  the  cut  arteries  were  found  open.  In  each  of  these  experi- 
ments there  was  but  little  alteration  perceived  in  the  orifices 
of  the  veins. 

(4.)  The  influence  of  cold  in  increasing  the  contraction  of 
a  divided  artery  has  been  referred  to:  it  has  been  shown, 
also,  by  Schwann,  in  an  experiment  on  the  mesentery  of  a 
living  toad.  Having  extended  the  mesentery  under  the  micro- 
scope, he  placed  upon  it  a  few  drops  of  water,  the  temperature 
of  which  was  some  degrees  lower  than  that  of  the  atmosphere. 
The  contraction  of  the  vessels  soon  commenced,  and  gradually 
increased  until,  at  the  expiration  of  ten  or  fifteen  minutes,  the 
diameter  of  the  canal  of  an  artery,  which  at  first  was  0.0724 
of  an  English  line,  was  reduced  to  0.0276.  The  arteries  then 
dilated  again,  and  at  the  expiration  of  half  an  hour  had  ac- 
quired nearly  their  original  size.  By  renewing  the  application 
of  the  water,  the  contraction  was  reproduced :  in  this  way  the 
experiment  could  be  performed  several  times  on  the  same  ar- 
tery. It  is  thus  proved,  that  cold  will  excite  contraction  in 
the  walls  of  very  small,  as  well  as  of  comparatively  large  ar- 
teries :  it  could  not  produce  such  contraction  in  a  merely  elastic 
substance ;  but  it  is  a  stimulus  to  the  organic  muscular  fibres 
in  many  other  parts,  as  well  as  in  the  arterial  coat ;  as,  e.  g., 
in  the  skin,  the  dartos,  and  the  walls  of  the  bronchi. 

(5.)  Lastly,  satisfactory  evidence  of  the  muscularity  of  the 
arterial  coats  is  furnished  by  the  experiments  of  Ed.  and  E. 
H.  Weber,  and  of  Professor  Kolliker,  in  which  they  applied 
the  stimulus  of  electro-magnetism  to  small  arteries. "  The  ex- 
periments of  the  Webers  were  performed  on  the  small  mesen- 
teric  arteries  of  frogs ;  and  the  most  striking  results  were  ob- 
tained when  the  diameter  of  the  vessels  examined  did  not 
exceed  from  to  -  of  a  Paris  line.  When  a  vessel  of  this 


FUNCTIONS    OF    MUSCULAR    COAT.  121 

size  was  exposed  to  the  electric  current,  its  diameter  in  from 
five  to  ten  seconds,  became  one-third  less,  and  the  area  of  its 
section  about  one-half.  On  continuing  the  stimulus,  the  nar- 
rowing gradually  increased,  until  the  calibre  of  the  tube  be- 
came from  three  to  six  times  smaller  than  it  was  at  first,  so 
that  only  a  single  row  of  blood-corpuscles  could  pass  along  it 
at  once ;  and  eventually  the  vessel  was  closed  and  the  current 
of  blood  arrested. 

With  regard  to  the  purpose  served  by  the  muscular  coat  of 
the  arteries,  there  appears  no  sufficient  reason  for  supposing 
that  it  assists,  to  more  than  a  very  small  degree,  in  propelling 
the  onward  current  of  blood.  Its  most  important  office  is  that 
of  regulating  the  quantity  of  blood  to  be  received  by  each 
part,  and  of  adjusting  it  to  the  requirements  of  each,  accord- 
ing to  various  circumstances,  but  chiefly  and  most  naturally, 
according  to  the  activity  with  which  the  functions  of  each 
part  are  at  different  times  performed.  The  amount  of  work 
done  by  each  organ  of  the  body  varies  at  different  times,  and 
the  variations  often  quickly  succeed  each  other,  so  that,  as  in 
the  brain,  for  example,  during  sleep  and  waking,  within  the 
same  hour  a  part  may  be  now  very  active  and  then  inactive. 
In  all  its  active  exercise  of  function,  such  a  part  requires  a 
larger  supply  of  blood  than  is  sufficient  for  it  during  the  times 
when  it  is  comparatively  inactive.  It  is  evident  that  the  heart 
cannot  regulate  the  supply  to  each  part  at  different  periods, 
neither  could  this  be  regulated  by  any  general  and  uniform 
contraction  of  the  arteries  ;  but  it  may  be  regulated  by  the 
power  which  the  arteries  of  each  part  have,  in  their  muscular 
tissue,  of  contracting  so  as  to  diminish,  and  of  passively  di- 
lating or  yielding  so  as  to  permit  an  increase  of,  the  supply  of 
blood,  according  as  the  requirements  of  the  part  may  demand. 
And  thus,  while  the  ventricles  of  the  heart  determine  the 
total  quantity  of  blood,  to  be  sent  onwards  at  each  contraction, 
and  the  force  of  its  propulsion,  and  while  the  large  and  merely 
elastic  arteries  distribute  it  and  equalizers  stream,  the  smaller 
arteries  with  muscular  tissue  add  to  these  two  purposes,  that  of 
regulating  and  determining,  according  to  its  requirements,  the 
proportion  of  the  whole  quantity  of  blood  which  shall  be  dis- 
tributed to  each  part. 

It  must  be  remembered,  however,  that  this  regulating  func- 
tion of  the  arteries  is  itself  governed  and  directed  by  the  ner- 
vous system. 

The  muscular  tissue  of  arteries  is  supplied  with  nerves 
chiefly,  if  not  entirely,  by  branches  from  the  sympathetic  sys- 
tem. These  so-called  vasomotor  nerves  are  again  connected, 
through  the  medium  of  ganglia,  with  the  fibres  from  the  sym- 


122  THE     CIRCULATION. 

pathetic  system  supplied  to  the  organs  nourished  by  these  same 
arteries.  Thus,  any  condition  in  these  organs  which  causes 
them  to  need  a  different  amount  of  blood,  whether  more  or 
less,  produces  a  certain  impression  on  their  nerves,  and  by 
these  the  impression  is  carried  to  the  ganglia,  and  thence  re- 
flected along  the  nerves  which  supply  the  arteries.  The  mus- 
cular element  of  these  vessels  responds  in  obedience  to  the 
impression  conveyed  to  it  by  the  nerves ;  and,  according  to  its 
contraction  or  dilatation,  is  a  larger  or  smaller  quantity  of 
blood  allowed  to  pass. 

Another  function  of  the  muscular  element  of  the  middle 
coat  of  arteries  is,  doubtless,  to  co-operate  with  the  elastic  in 
adapting  the  calibre  of  the  vessels  to  the  quantity  of  blood 
which  they  contain.  For  the  amount  of  fluid  in  the  blood- 
vessels varies  very  considerably  even  from  hour  to  hour,  and 
can  never  be  quite  constant ;  and  were  the  elastic  tissue  only 
present,  the  pressure  exercised  by  the  walls  of  the  containing 
vessels  on  the  contained  blood  would  be  sometimes  very  small, 
and  sometimes  inordinately  great.  The  presence  of  a  muscu- 
lar element,  however,  provides  for  a  certain  uniformity  in  the 
amount  of  pressure  exercised  ;  and  it  is  by  this  adaptive,  uni- 
form, gentle,  muscular  contraction,  that  the  tone  of  the  blood- 
vessels is  maintained.  Deficiency  of  this  tone  is  the  cause  of 
the  soft  and  yielding  pulse,  and  its  unnatural  excess  of  the 
hard  and  tense  one. 

The  elastic  and  muscular  contraction  of  an  artery  may  also 
be  regarded  as  fulfilling  a  natural  purpose  when,  the  artery 
being  cut,  it  first  limits  and  then,  in  conjunction  with  the  coag- 
ulated fibrin,  arrests  the  escape  of  blood.  It  is  only  in  conse- 
quence of  such  contraction  and  coagulation  that  we  are  free 
from  danger  through  even  very  slight  wounds ;  for  it  is  only 
when  the  artery  is  closed  that  the  processes  for  the  more  perma- 
nent and  secure  prevention  of  bleeding  are  established. 

Mr.  Savory  has  shown  that  the  natural  state  of  all  arteries, 
in  regard  at  least  to  their  length,  is  one  of  tension — that  they 
are  always  more  or  less  stretched,  and  ever  ready  to  recoil  by 
virtue  of  their  elasticity,  whenever  the  opposing  force  is  re- 
moved. The  extent  to  which  the  divided  extremities  of  ar- 
teries retract  is  a  measure  of  this  tension,  not  of  their  elasticity. 

From  what  has  been  said  in  the  preceding  pages,  it  appears 
that  the  office  of  the  arteries  in  the  circulation  is, — 1st,  the 
conveyance  and  distribution  of  blood  to  the  several  parts  of 
the  body ;  2d,  the  equalization  of  the  current,  and  the  con- 
version of  the  pulsatile  jetting  movement  given  to  the  blood 
by  the  ventricles,  into  a  uniform  flow ;  3d,  the  regulation  of 


THE    PULSE.  123 

the  supply  of  blood  to  each  part,  in  accordance  with  its  de- 
mands. 

The  Pulse. 

The  jetting  movement  of  the  blood,  which,  as  just  stated, 
it  is  one  of  the  offices  of  the  arteries  to  change  into  a  uni- 
form motion,  is  the  cause  of  the  pulse,  and  therefore  needs  a 
separate  consideration.  We  have  already  said,  that  as  the 
blood  is  not  able  to  pass  through  the  arteries  so  quickly  'as  it 
is  forced  into  them  by  the  ventricle,  on  account  of  the  resist- 
ance it  experiences  in  the  capillaries,  a  part  of  the  force  with 
which  the  heart  impels  the  blood  is  exercised  upon  the  walls 
of  the  vessels  which  it  distends.  The  distension  of  each  artery 
increases  both  its  length  and  its  diameter.  In  their  elonga- 
tion, the  arteries  change  their  form,  the  straight  ones  becoming 
curved,  or  having  such  a  tendency,  and  those  already  curved 
becoming  more  so  ;l  but  they  recover  their  previous  form  as  well 
as  their  diameter  when  the  ventricular  contraction  ceases,  and 
their  elastic  walls  recoil.  The  increase  of  their  curves  which 
accompanies  the  distension  of  arteries,  and  the  succeeding  re- 
coil, may  be  well  seen  in  the  prominent  temporal  artery  of  an 
old  person.  The  elongation  of  the  artery  is  in  such  a  case 
quite  manifest. 

The  dilatation  or  increase  of  the  diameter  of  the  artery  is 
less  evident.  In  several  reptiles,  it  may  be  seen  without  aid, 
in  the  immediate  vicinity  of  the  heart,  and  it  may  be  watched, 
with  a  simple  magnifying  glass,  in  the  aorta  of  the  tadpole. 
Its  slight  amount  in  the  smaller  arteries,  the  difficulty  of 
observing  it  in  opaque  parts,  and  the  rapidity  with  which  it 
takes  place,  are  sufficient  to  account  for  its  being,  in  Mam- 
malia, imperceptible  to  the  eye.  But  in  these  also  experi- 
ment has  proved  its  occurrence.  Flourens,  in  evidence  of  such 
dilatation,  says  he  encircled  a  large  artery  with  a  thin  elastic 
metallic  ring  cleft  at  one  point,  and  that  at  the  moment  of 
pulsation  the  cleft  part  became  perceptibly  widened. 

This  dilatation  of  an  artery,  and  the  elongation  producing 
curvature,  or  increasing  the  natural  curves,  are  sensible  to 
the  finger  placed  over  the  vessel,  and  produce  the  pulse.  The 
mind  cannot  distinguish  the  sensation  produced  by  the  dilata- 
tion from  that  produced  by  the  elongation  and  curving ;  that 
which  it  perceives  most  plainly,  however,  is  the  dilatation.2 

1  There  is,  perhaps,  an  exception  to  this  in  the  case  of  the  aorta,  of 
which  the  curve  is  by  some  supposed  to  be  diminished  when  it  is  elon- 
gated ;  but  if  this  be  so,  it  is  because  only  one  end  of  the  arch  is  im- 
movable;  the  other  end,  with  the  heart/may  move  forward  slightly 
when  the  ventricles  contract. 

8  For  this  fact,  which  is  contrary  to  the  commonly  accepted  doc- 


124  THE    CIRCULATION. 

The  pulse — due  to  any  given  beat  of  the  heart — is  not  per- 
ceptible at  the  same  moment  in  all  the  arteries  of  the  body. 
Thus  it  can  be  felt  in  the  carotid  a  very  short  time  before  it  is 
perceptible  in  the  radial  artery,  and  in  this  vessel  again  before 
the  dorsal  artery  of  the  foot.  The  delay  in  the  beat  is  in  pro- 
portion to  the  distance  of  the  artery  from  the  heart,  but  the 
difference  in  time  between  the  beat  of  any  two  arteries  never 
exceeds  probably  %  to  £  of  a  second. 

A  great  deal  of  light  has  been  thrown  on  what  may  be  called 
the  form  of  the  pulse  by  the  sphygmograph  (Figs.  42  and  43). 
The  principle  on  which  the  sphygmograph  acts  is  very  simple 
(see  Fig.  42).  The  small  button  replaces  the  finger  in  the 
ordinary  act  of  taking  the  pulse  and  is  made  to  rest  lightly  on 
the  artery,  the  pulsations  of  which  it  is  desired  to  investigate. 
The  up-and-down  movement  of  the  button  is  communicated  to 
the  lever,  to  the  hinder  end  of  which  is  attached  a  slight  spring, 
which  allows  the  lever  to  move  up,  at  the  same  time  that  it  is 
just  strong  enough  to  resist  its  making  any  sudden  jerk,  and 
in  the  interval  of  the  beats  also  to  assist  in  bringing  it  back  to 
its  original  position.  For  ordinary  purposes,  the  instrument 
is  bound  on  the  wrist  (Fig.  43). 

trine,  I  am  indebted  to  my  friend,  Dr.  Hensley,  who  has  kindly  fur- 
nished me  with  the  following  note  on  the  subject: 

By  determining  the  conditions  of  equilibrium  of  a  portion  of  artery 
supposed  cylindrical  and  filled  with  blood  at  a  given  pressure,  it  is 
easily  shown  that  the  transverse  tension  is  double" the  longitudinal. 

Also  it  may  be  shown  experimentally  that,  if  strips  of  equal  breadth, 
cut  in  the  two  directions  from  one  of 'the  larger  arteries,  be  stretched 
by  equal  weights,  the  stretching  of  tbe  transverse  slip  is  somewhat 
greater  than  that  of  the  longitudinal  one. 

(By  the  word  stretching  is  to  be  understood  amount  of  stretching, 
and  not  increase  of  length :  it  may  be  measured  by  the  ratio  which  the 
increase  of  length  bears  to  the  original  length :  thus  things  wliose 
natural  lengths  are  5  and  10  inches  are  equally  stretched  when  their 
lengths  are  wade  6  and  12  inches  respectively.) 

Such  experiments  also  show  that,  within  certain  limits,  the  stretch- 
ing of  each  strip  varies  directly  as  its  tension. 

Hence  it  will  be  seen  that  the  transverse  stretching  of  an  artery, 
when  filled  with  blood,  must  be  somewhat  more  than  double  its  longi- 
tudinal stretching. 

This  being  true  for  different  blood  pressures,  the  difference  between 
the  transverse  stretchings  for  different  pressures  must  be  somewhat 
more  than  double  the  difference  between  the  corresponding  longitu- 
dinal stretchings;  and  thus  we  can  hardly  be  justified  in  saying  that 
the  increase  of  longitudinal  stretching  which  takes  place  with  the 
pulse  is  greater  than  the  increase  of  transverse  stretching. 

It  must  also  be  remembered  that  the  arteries  are,  under  all  circum- 
stances, naturally  in  a  state  of  tension  longitudinally,  and  that  their 
length,  therefore,  cannot  be  increased  at  all  until  the  blood  pressure 
is  increased  beyond  a  certain  point. — ED.) 


P  U  L  8  E  -  T  R  A  C I N  G  S. 


125 


It  is  evident  that  the  beating  of  the  pulse  with  the  reaction 
of  the  spring  will  cause  an  up-and-down  movement  of  the 
lever,  and  if  the  extremity  of  the  latter  be  inked,  it  will  write 


FIG.  42. 


Diagram  of  the  mode  of  action  of  thesphygmograph. 

the  effect  on  the  card,  which  is  made  to  move  by  clockwork  in 
the  direction  of  the  arrow.  Thus  a  tracing  of  the  pulse  is  ob- 
tained, and  in  this  way  much  more  delicate  effects  can  be  seen, 
than  can  be  felt  on  the  application  of  the  finger. 

FIG.  43. 


The  sphygmograph  applied  to  the  arm. 

Fig.  44  represents  a  healthy  pulse-tracing  of  the  radial 
artery,  but  somewhat  deficient  in  tone.  On  examination,  we 
see  that  the  up-stroke  which  represents  the  beat  of  the  pulse 
is  a  nearly  vertical  line,  while  the  down-stroke  is  very  slanting, 
and  interrupted  by  a  slight  reascent.  The  more  vigorous  the 
pulse,  if  it  be  healthy,  the  less  is  this  reasceut,  and  vice  versd. 
Fig.  45  represents  the  tracing  of  a  healthy  pulse  in  which  the 
tone  of  the  vessel  is  better  than  in  the  last  instance,  and  the 
down-stroke  is  therefore  less  interrupted. 

Sometimes  the  up-stroke  has  a  double  apex,  as  in  Fig.  46. 
This  will  be  explained  hereafter. 

11 


126 


THE    CIRCULATION. 


Before  proceeding  to  consider  the  formation  of  the  pulse,  as 
shown  by  these  tracings,  it  is  necessary  to  consider  what  are 
the  elements  combined  to  produce  it. 

Fig.  44. 


FIG.  44.  Pulse-tracing  of  radial  artery,  somewhat  deficient  in  tone. 

FIG.  45.  Firm  and  long  pulse  of  vigorous  health. 

FIG.  46.  Pulse-tracing  of  radial  artery,  with  double  apex. 

The  above  tracings  are  taken  from  Dr.  Sanderson's  work  "  On  the  Sphygmograph.'1 

The  heart  at  regular  intervals  discharges  a  certain  quantity 
of  blood  into  the  arteries  and  their  branches,  already  filled, 
though  not  distended  to  the  utmost,  with  fluid.  This  fresh 
quantity  of  blood  obtains  entrance  by  the  yielding  of  the 
artery's  elastic  walls,  and,  on  the  cessation  of  the  propelling 
force,  and  when  these  walls  recoil,  the  blood  is  prevented  from 
returning  into  the  ventricle  whence  it  is  issued,  by  the  shut- 
ting of  the  semilunar  valves  in  the  manner  before  described 
(p.  103).  The  pressure,  therefore,  which  is  exercised  on  the 
blood  by  the  contracting  arterial  walls,  will  cause  it  to  travel 
in  a  direction  away  from  the  heart,  or,  in  other  words,  towards 
the  capillaries  and  veins. 

It  was  formerly  supposed  that  the  pulse  was  caused  not  by 
the  direct  action  of  the  ventricle,  but  by  the  propagation  of  a 
wave  in  consequence  of  the  elastic  recoil  of  the  large  arteries, 
after  their  distension ;  and  successive  acts  of  dilatation  and 
recoil,  extending  along  the  arteries  in  the  direction  of  the  cir- 
culation, were  supposed  to  account  for  the  latter  appearance 
of  the  pulse  in  the  vessels  most  distant  from  the  heart.  The 
fact,  however,  that  the  pulse  is  perceptible  in  every  part  of  the 
arterial  system  previous  to  the  occurrence  of  the  second  sound 
of  the  heart,  that  is,  previous  to  the  closure  of  the  aortic 


PULSE-TRACINGS.  127 

valves,  is  a  fatal  objection  to  this  theory.  For,  if  the  pulse 
were  theVeffect  of  a  wave  propagated  by  the  alternate  dilata- 
tion and  contraction  of  successive  portions  of  the  arterial  tube, 
it  ought,  in  all  the  arteries  except  those  nearest  to  the  heart, 
to  follow  or  coincide  with,  but  could  never  precede,  the  second 
sound  of  the  heart ;  for  the  first  effect  of  the  elastic  recoil  of 
the  arteries  first  dilated  is  the  closure  of  the  aortic  valves ;  and 
their  closure  produces  the  second  sound. 

The  theory  which  seems  to  reconcile  all  the  facts  of  the  case, 
and  especially  those  two  which  appear  most  opposed,  namely, 
that  the  pulse  always  precedes  the  second  sound  of  the  heart, 
and  yet  is  later  in  the  arteries  far  from  the  heart  than  in  those 
near  it,  may  be  thus  stated :  It  supposes  that  the  blood  which 
is  impelled  onwards  by  the  left  ventricle  does  not  so  impart  its 
pressure  to  that  which  the  arteries  already  contain,  as  to  dilate 
the  whole  arterial  system  at  once ;  but  that  it  enters  the  ar- 
teries, it  displaces  and  propels  that  which  they  before  con- 
tained, and  flows  on  with  what  may  be  called  a  head-wave,  like 
that  which  is  formed  when  a  rapid  stream  of  water  overtakes 
another  moving  more  slowly.  The  slower  stream  offers  resist- 
ance to  the  more  rapid  one,  till  their  velocities  are  equalized; 
arid  because  of  such  resistance,  some  of  the  force  of  the  more 
rapid  stream  of  blood  just  expelled  from  the  ventricle,  is 
diverted  laterally,  and  with  the  rising  of  the  wave  the  arteries 
nearest  the  heart  are  dilated  and  elongated.  They  do  not  at 
once  recoil,  but  continue  to  be  distended  so  long  as  blood  is 
entering  them  from  the  ventricle.  The  wave  at  the  head  of 
the  more  rapid  stream  of  blood  runs  on,  propelled  and  main- 
tained in  its  velocity  by  the  continuous  contraction  of  the  ven- 
tricle ;  and  it  thus  dilates  in  succession  every  portion  of  the 
arterial  system,  and  produces  the  pulse  in  all.  At  length,  the 
whole  arterial  system  (wherein  a  pulse  can  be  felt)  is  dilated ; 
and  at  this  time,  when  the  wave  we  have  supposed  has  reached 
all  the  smaller  arteries,  the  entire  system  may  be  said  to  be 
simultaneously  dilated ;  then  it  begins  to  contract,  and  the 
contractions  of  its  several  parts  ensue  in  the  same  succession 
as  the  dilatations,  commencing  at  the  heart.  The  contraction 
of  the  first  portion  produces  the  closure  of  the  valves  and  the 
second  sound  of  the  heart ;  and  both  it  and  the  progressive 
contractions  of  all  the  more  distant  parts  maintain,  as  already 
said,  that  pressure  on  the  blood  during  the  inaction  of  the 
ventricle,  by  which  the  stream  of  the  arterial  blood  is  sustained 
between  the  jets,  and  is  finally  equalized  by  the  time  it  reaches 
the  capillaries. 

It  may  seem  an  objection  to  this  theory,  that  it  would  prob- 
ably require  a  larger  quantity  of  blood  to  dilate  all  the  ar- 


128  THE    CIRCULATION. 

teries  than  can  be  discharged  by  the  ventricle  at  each  contrac- 
tion. But  the  quantity  necessary  for  such  a  purpose  is  less 
than  might  be  supposed.  Injections  of  the  arteries  prove  that, 
including  all  down  to  those  of  about  one-eighth  of  a  line  in 
diameter,  they  do  not  contain  on  an  average  more  than  one 
and  a  half  pints  of  fluid,  even  when  distended.  There  can  be 
no  doubt,  therefore,  that  the  three  or  four  ounces  which  the 
ventricle  is  supposed  to  discharge  at  each  contraction,  being 
added  to  that  which  already  fills  the  arteries,  would  be  suffi- 
cient to  distend  them  all. 

A  distinction  must  be  carefully  made  between  the  passage 
of  the  wave  along  the  arteries,  and  the  velocity  of  the  stream 
(p.  131)  of  blood.  Both  wave  and  current  are  present;  but  the 
rates  at  which  they  travel  are  very  different,  that  of  the  wave 
being  twenty  or  thirty  times  as  great  as  that  of  the  current. 

Returning  now  to  the  consideration  of  the  pulse-tracings 
(p.  126),  it  may  be  remarked  that,  in  each,  the  up-stroke  cor- 
responds with  the  period  during  which  the  ventricle  is  con- 
tracting ;  the  down-stroke,  with  the  interval  between  its  con- 
tractions, or  in  other  words  with  the  recoil,  after  distension, 
of  the  elastic  arteries.  In  the  large  arteries,  when  at  least 
there  is  much  loss  of  tone,  the  up-stroke  is  double,  the  almost 
instantaneous  propagation  of  the  force  of  contraction  of  the 
left  ventricle  along  the  column  of  blood  in  the  arteries,  or  the 
percussion  impulse,  as  it  is  termed  by  Dr.  Sanderson,  being 
sufficiently  strong  to  jerk  up  the  lever  for  an  instant,  while  the 
wave  of  blood,  rather  more  slowly  propagated  from  the  ven- 
tricle, catches  it,  so  to  speak,  as  it  begins  to  fall,  and  again 
slightly  raises  it. 

In  the  radial  artery  tracings,  on  the  other  hand,  we  see  that 
the  up-stroke.  is  single.  In  this  case  the  percussion-impulse  is 
not  sufficiently  strong  to  jerk  up  the  lever  and  produce  an 
effect  distinct  from  that  of  the  systolic  wave  which  immedi- 
ately follows  it,  and  which  continues  and  completes  the  dis- 
tension. In  cases  of  feeble  arterial  tension,  however,  the  per- 
cussion-impulse may  be  traced  by  the  sphygmograph,  not  only 
in  the  carotid  pulse,  but  to  a  less  extent  in  the  radial  also  (as 
in  Fig.  46). 

In  looking  now  at  the  down-stroke  (Fig.  44)  in  the  tracings, 
we  see  that  in  the  case  of  an  artery  with  deficient  tone,  it  is  in- 
terrupted by  a  well-marked  notch,  or  in  other  words,  that  the 
descent  is  interrupted  by  a  slight  uprising.  There  are  indica- 
tions also  of  slighter  irregularities  or  vibrations  during  the  fall 
of  the  lever ;  while  these  are  alone  to  be  seen  in  the  pulse  of 
health,  or  in  other  words,  when  the  walls  of  the  artery  are  of 
good  tone  (Fig.  45).  In  some  cases  of  disease  the  reascent  is 


FO1RCE    OF     BLOOD     IN     ARTERIES. 


129 


FIG.  47. 


so  considerable  as  to  be  perceptible  to  the  finger,  and  this 
double  beat  has  received  the  technical  name  of  "dicrotous" 
pulse.  As  a  diseased  condition  this  has  long  been  recognized, 
but  it  is  only  since  the  invention  of  the  sphygmograph  that  it 
ha«  been  found  to  belong  in  a  certain  degree  to  the  normal 
pulse  also. 

Various  theories  have  been  framed  to  account  for  the  dicro- 
tism  of  the  pulse.  By  some,  it  is  supposed  to  be  due  to  the 
aortic  valves,  the  sudden  closure  of  which  stops  the  incipient 
regurgitation  of  blood  into  the  ventricle,  and  causes  a  mo- 
mentary rebound  throughout  the  arterial  system ;  while  Dr. 
Sanderson  considers  it  to  be  caused  by  a  kind  of  rebound  from 
the  periphery  rather  than  from  the  central  part  of  the  circu- 
lating apparatus. 

Force  of  the  Blood  in  the  Arteries. 

The  force  with  which  the  ventricles  act  in  their  contraction, 
and  the  reasons  for  believing  it  sufficient  for  the  circulation  of 
the  blood,  have  been  already  mentioned.  Both  calculation 
and  experiment  have  proved  that  very  little  of  this  force  is 
consumed  in  the  arteries.  Dr. 
Thomas  Young  calculated  that 
the  loss  of  force  in  overcoming 
friction  and  other  hindrances  in 
the  arteries  would  be  so  slight, 
that  if  one  tube  were  introduced 
into  the  aorta,  and  another  into 
any  other  artery,  even  into  one  as 
fine  as  hair,  the  blood  would  rise 
in  the  tube  from  the  small  vessel 
to  within  two  inches  of  the  height 
to  which  it  would  rise  from  the 
large  vessel.  The  correctness  of 
the  calculation  is  established  by 
the  experiments  of  Poiseuille,  who 
invented  an  instrument  named  a 
hsemadynamometer,  for  estimating 
the  statical  pressure  exercised  by 
the  blood  upon  the  walls  of  the 
arteries.  It  consists  of  a  long  glass 
tube,  bent  so  as  to  have  a  short 
horizontal  portion  (b,  Fig.  47), 
a  branch  (a)  descending  at  right 
angles  from  it,  and  a  long  ascend- 
ing branch  (c).  Mercury  poured 
into  the  ascending  and  descending 
portions  will  necessarily  have  the 


130  THE     CIRCULATION. 

same  level  in  both  branches,  and  in  a  vertical  position  the 
height  of  its  column  must  be  the  same  in  both.  If,  now,  the 
blood  is  made  to  flow  from  an  artery,  through  the  horizontal 
portion  of  the  tube  (which  should  contain  a  solution  of  carbo- 
nate of  potash  to  prevent  coagulation)  into  the  descending 
branch,  it  will  exert  on  the  mercury  a  pressure  equal  to  the 
force  by  which  it  is  moved  in  the  arteries ;  and  the  mercury 
will,  in  consequence,  descend  in  this  branch,  and  ascend  in 
the  other.  The  depth  to  which  it  sinks  in  the  one  branch, 
added  to  the  height  to  which  it  rises  in  the  other,  will  give  the 
whole  height  of  the  column  of  mercury  which  balances  the 
pressure  exerted  by  the  blood ;  the  weight  of  the  blood,  which 
takes  the  place  of  the  mercury  in  the  descending  branch,  and 
which  is  more  than  ten  times  less  than  the  same  quantity  of 
quicksilver,  being  subtracted.  Poiseuille  thus  calculated  the 
force  with  which  the  blood  moves  in  an  artery,  according  to 
the  laws  of  hydrostatics,  from  the  diameter  of  the  artery,  and 
the  height  of  the  column  of  quicksilver ;  that  is  to  say,  from 
the  weight  of  a  column  of  mercury,  whose  base  is  a  circle  of 
the  same  diameter  as  the  artery,  and  whose  height  is  equal  to 
the  difference  in  the  levels  of  the  mercury  in  the  two  branches 
of  the  instrument.  He  found  the  blood's  pressure  equal  in  all 
the  arteries  examined ;  difference  in  size,  and  distance  from 
the  heart  being  unattended  by  any  corresponding  difference  of 
force  in  the  circulation.  The  height  of  the  column  of  mercury 
displaced  by  the  blood  was  the  same  in  all  the  arteries  of  the 
same  animal.  The  correctness  of  these  views  having  been 
questioned,  Poiseuille  has  recently  repeated  his  observations, 
and  obtained  the  same  results. 

From  the  mean  result  of  several  observations  on  horses  and 
dogs,  he  calculated  that  the  force  with  which  the  blood  is 
moved  in  any  large  artery,  is  capable  of  supporting  a  column 
of  mercury  six  inches  and  one  and  a  half  lines  in  height,  or  a 
column  of  water  seven  feet  one  line  in  height.  With  these  re- 
sults, the  more  recent  observations  of  other  experimenters 
closely  accord.  Poiseuille's  experiments  having  thus  shown  to 
him  that  the  force  of  the  blood's  motion  is  the  same  in  the  most 
different  arteries,  he  concluded  that,  to  measure  the  amount  of 
the  blood's  pressure  in  any  artery  of  which  the  calibre  is  known, 
it  is  necessary  merely  to  multiply  the  area  of  a  transverse  sec- 
tion of  a  vessel  by  the  height  of  the  column  of  mercury  which 
is  already  known  to  be  supported  by  the  force  of  the  blood  in 
any  part  of  the  arterial  system.  The  weight  of  a  column  of 
mercury  of  the  dimensions  thus  found,  will  represent  the  pres- 
sure exerted  by  the  column  of  blood.  And  assuming  that  the 
mean  of  the  greatest  and  least  height  of  the  column  of  mercury 


THE    CAPILLARIES.  131 

found,  by  experiments  on  different  animals,  to  be  supported  by 
the  force  of  the  blood  in  them,  is  equivalent  to  the  height  of 
the  column  which  the  force  of  the  blood  in  the  human  aorta 
would  support,  he  calculated  that  about  4  Ibs.  4  oz.  avoirdu- 
pois would  indicate  the  static  force  with  which  the  blood  is  im- 
pelled into  the  human  aorta.  By  the  same  calculation,  he 
estimated  the  force  of  the  circulation  in  the  aorta  of  the  mare 
to  be  about  11  Ibs.  9  oz.  avoirdupois:  and  that  in  the  radial 
artery  at  the  human  wrist  only  4  drs.  We  have  already  seen 
that  the  muscular  force  of  the  right  ventricle  is  equal  to  only 
one-half  that  of  the  left,  consequently,  if  Poiseuille's  estimate 
of  the  latter  be  correct,  the  force  with  which  the  blood  is  pro- 
pelled into  the  lungs  will  only  be  equal  to  2  Ibs.  2  oz.  avoir- 
dupois. 

The  amounts  above  stated  indicate  the  pressure  exerted  by 
the  blood  at  the  several  parts  of  the  arterial  system  at  the  time 
of  the  ventricular  contraction.  During  the  dilatation,  this 
pressure  is  somewhat  diminished.  Hales  observed,  that  the 
column  of  blood  in  the  tube  inserted  into  an  artery,  falls  an 
inch,  or  rather  more,  after  each  pulse ;  Ludwig  has  observed 
the  same,  and  recorded  it  more  minutely.  The  pressure  is  also 
influenced  by  the  various  circumstances  which  affect  the  action 
of  the  heart ;  the  diminution  or  increase  of  the  pressure  being 
proportioned  to  the  weaker  or  stronger  action  of  this  organ. 
Valentin  observed  that,  on  increasing  the  amount  of  blood  by 
the  injection  of  a  fresh  quantity  into  it,  the  pressure  in  the 
vessels  was  also  increased,  while  a  contrary  effect  ensued  on 
diminishing  the  quantity  of  blood. 

Velocity  of  the  Blood  in  the  Arteries. 

The  velocity  of  the  stream  of  blood  is  greater  in  the  arteries 
than  in  any  other  part  of  the  circulatory  system,  and  in  them 
it  is  greatest  in  the  neighborhood  of  the  heart,  and  during  the 
ventricular  systole;  the  rate  of  movement  diminishing  during 
the  diastole  of  the  ventricles,  and  in  the  parts  of  the  arterial 
system  most  distant  from  the  heart.  From  Volkmann's  ex- 
periments with  thehsemodromometer,  it  may  be  concluded  that 
the  blood  moves  in  the  large  arteries  near  the  heart  at  the  rate 
of  about  ten  or  twelve  inches  per  second.  Vierordt  calculated 
the  rapidity  of  the  stream  at  about  the  same  rate  in  the  arteries 
near  the  heart,  and  at  two  and  a  quarter  inches  per  second  in 
the  arteries  of  the  foot. 

THE   CAPILLARIES. 

In  all  organic  textures,  except  some  parts  of  the  corpora 
cavernosa  of  the  penis,  and  of  the  uterine  placenta,  and  of  the 


132 


THE    CIRCULATION. 


FIG.  48. 


spleen,  the  transmission  of  the  blood  from  the  minute  branches 
of  the  arteries  to  the  minute  veins  is  effected  through  a  net- 
work of  microscopic  vessels,  in  the  meshes  of  which  the  proper 
substance  of  the  tissue  lies  (Fig.  48).  This  may  be  seen  in  all 
minutely  injected  preparations ;  and  during  life,  by  the  aid  of 
the  microscope,  in  any  transparent  vascular  parts, — such  as  the 
web  of  the  frog's  foot,  the  tail  or  external  branchiae  of  the  tad- 
pole, or  the  wing  of  the  bat. 

The  ramifications  of  the  minute  arteries  form  repeated  an- 
astomoses with  each  other  and  give  off  the  capillaries  which, 
by  their  anastomoses,  compose  a  continuous  and  uniform  net- 
work, from  which  the  venous  radicles,  on  the  other  hand,  take 
their  rise.  The  reticulated  vessels  connecting  the  arteries  and 
veins  are  called  capillary,  on  account 
of  their  minute  size  ;  and  intermedi- 
ate vessels,  on  account  of  their  po- 
sition. The  point  at  which  the  ar- 
teries terminate  and  the  minute  veins 
commence,  cannot  be  exactly  defined, 
for  the  transition  is  gradual ;  but  the 
intermediate  network  has,  neverthe- 
less, this  peculiarity,  that  the  small 
vessels  which  compose  it  maintain 
the  same  diameter  throughout ;  they 
do  not  diminish  in  diameter  in  one 
direction,  like  arteries  and  veins  ;  and 
the  meshes  of  the  network  that  they 
compose  are  more  uniform  in  ghape 
and  size  than  those  formed  by  the 
anastomoses  of  the  minute  arteries 
and  veins. 

The  structure  of  the  capillaries  is 
much  more  simple  than  that  of  the 
arteries  or  veins.  Their  walls  are 
composed  of  a  single  layer  of  elon- 
gated or  radiate,  flattened  and  nu- 
cleated cells,  so  joined  and  dovetailed 
together  as  to  form  a  continuous 
transparent  membrane  (Fig.  49). 
Outside  these  cells,  in  the  larger  cap- 
illaries, there  is  a  structureless,  or 
very  finely  fibrillated  membrane,  on  the  inner  surface  of  which 
they  are  laid  down. 

The  diameter  of  the  capillary  vessels  varies  somewhat  in  the 
different  textures  of  the  body,  the  most  common  size  being 
about  --th  of  an  inch.  Among  the  smallest  may  be  men- 


Bloodvessels  of  an  intestinal 
villas,  representing  the  ar- 
rangement of  capillaries  be- 
tween the  ultimate  venous  and 
arterial  branches ;  a,  a,  the  ar- 
teries; 6,  the  vein. 


THE    CAPILLARIES. 


133 


tioned  those  of  the  brain,  and  of  the  follicles  of  the  mucous 
membrane  of  the  intestines ;  among  the  largest,  those  of  the 
skin,  and  especially  those  of  the  medulla  of  bones. 

The  form  of  the  capillary  network  presents  considerable 
variety  in  the  different  textures  of  the  body :  the  varieties  con- 
sisting principally  of  modifications  of  two  chief  kinds  of  mesh, 
the  rounded  and  the  elongated.  That  kind  in  which  the  meshes 
or  interspaces  have  a  roundish  form  is  the  most  common,  and 
prevails  in  those  parts  in  which  the  capillary  network  is  most 


FIG.  49. 


Magnified  view  of  capillary  vessels  from  the  bladder  of  the  cat.— A,  V,  an  artery 
and  a  vein ;  i,  transitional  vessel  between  them  and  c  c,  the  capillaries.  The  muscu- 
lar coat  of  the  larger  vessels  is  left  out  in  the  figure  to  allow  the  epithelium  to  be 
seen  at  c',  a  radiate  epithelium  scale  with  four  pointed  processes,  running  out  upon 
the  four  adjoining  capillaries  (after  Chrzonszczewesky,  Virch.  Arch.  1856)- 

dense,  such  as  the  lungs  (Fig.  50),  most  glands,  and  mucous 
membranes,  and  the  cutis.  The  meshes  of  this  kind  of  net- 
work are  not  quite  circular,  but  more  or  less  angular,  some- 
times presenting  a  nearly  regular  quadrangular  or  polygonal 
form,  but  being  more  frequently  irregular.  The  capillary  net- 
work with  elongated  meshes  (Fig.  51)  is  observed  in  parts  in 
which  the  vessels  are  arranged  among  bundles  of  fine  tubes  or 
fibres,  as  in  muscles  and  nerves.  In  such  parts,  the  meshes 

12 


134 


THE    CIRCULATION. 


usually  have  the  form  of  a  parallelogram,  the  short  sides  of 
which  may  be  from  three  to  eight  or  ten  times  less  than  the 
long  ones ;  the  long  sides  always  corresponding  to  the  axis  of 


FIG.  50. 


FIG.  51. 


FIG.  50. — Network  of  capillary  vessels  of  the  air-cells  of  the  horse's  lung,  magnified 
a,  a,  capillaries  proceeding  from  6,  6,  terminal  branches  of  the  pulmonary  artery 
(after  Frey). 

FIG.  51. — Injected  capillary  vessels  of  muscle,  seen  with  a  low  magnifying  power 
(Sharpey). 

the  fibre  or  tube,  by  which  it  is  placed.  The  appearance  of 
both  the  rounded  and  elongated  meshes  is  much  varied  accord- 
ing as  the  vessels  composing  them  have  a  straight  or  tortuous 
form.  Sometimes  the  capillaries  have  a  looped  arrangement, 
a  single  capillary  projecting  from  the  common  network  into 
some  prominent  organ,  and  returning  after  forming  one  or 
more  loops,  as  in  the  papillae  of  the  tongue  and  skin.  What- 
ever be  the  form  of  the  capillary  network  in  any  tissue  or 
organ,  it  is,  as  a  rule,  found  to  prevail  in  the  corresponding 
parts  of  all  animals. 

The  number  of  the  capillaries  and  the  size  of  the  meshes  in 
different  parts  determine  in  general  the  degree  of  vascularity 
of  those  parts.  The  parts  in  which  the  network  of  capillaries 
is  closest,  that  is,  in  which  the  meshes  or  interspaces  are  the 
smallest,  are  the  lungs  and  the  choroid  membrane  of  the  eye. 
In  the  iris  and  ciliary  body  the  interspaces  are  somewhat 
wider,  yet  very  small.  In  the  human  liver,  the  interspaces 
are  of  the  same  size,  or  even  smaller  than  the  capillary  vessels 


THE    CAPILLARIES.  135 

themselves.  In  the  human  lung  they  are  smaller  than  the 
vessels ;  in  the  human  kidney,  and  in  the  kidney  of  the  dog, 
the  diameter  of  the  injected  capillaries,  compared  with  that 
of  the  interspaces,  is  in  the  proportion  of  one  to  four,  or  of  one 
to  three.  The  brain  receives  a  very  large  quantity  of  blood  ; 
but  the  capillaries  in  which  the  blood  is  distributed  through 
its  substance  are  very  minute,  and  less  numerous  than  in  some 
other  parts.  Their  diameter,  according  to  E.  H.  Weber,  com- 
pared with  the  long  diameter  of  the  meshes,  being  in  the  pro- 
portion of  one  to  eight  or  ten  ;  compared  with  the  transverse 
diameter,  in  the  proportion  of  one  to  four  or  six.  In  the  mu- 
cous membranes — for  example,  in  the  conjunctiva — and  in  the 
cutis  vera,  the  capillary  vessels  are  much  larger  than  in  the 
brain,  and  the  interspaces  narrower, — namely,  not  more  than 
three  or  four  times  wider  than  the  vessels.  In  the  periosteum 
the  meshes  are  much  larger.  In  the  cellular  coat  of  arteries, 
the  width  of  the  meshes  is  ten  times  that  of  the  vessels  (Henle). 

It  may  be  held  as  a  general  rule,  that  the  more  active  the 
functions  of  an  organ  are,  the  more  vascular  it  is;  that  is,  the 
closer  is  its  capillary  network  and  the  larger  its  supply  of 
blood.  Hence  the  narrowness  of  the  interspaces  in  all  glandu- 
lar organs,  in  mucous  membranes,  and  in  growing  parts ;  their 
much  greater  width  in  bones,  ligaments,  and  other  very  tough 
and  comparatively  inactive  tissues  ;  and  the  complete  absence 
of  vessels  in  cartilage,  the  dense  tendons  of  adults,  and  such 
parts  as  those  in  which,  probably,  very  little  organic  change 
occurs  after  they  are  once  formed.  But  the  general  rule  must 
be  modified  by  the  consideration,  that  some  organs,  such  as 
the  brain,  though  they  have  small  and  not  very  closely  ar- 
ranged capillaries,  may  receive  large  supplies  of  blood  by 
reason  of  its  more  rapid  movement.  When  an  organ  has 
large  arterial  trunks  and  a  comparatively  small  supply  of 
capillaries,  the  movement  of  the  blood  through  it  will  be  so 
quick,  that  it  may,  in  a  given  time,  receive  as  much  fresh 
blood  as  a  more  vascular  part  with  smaller  trunks,  though  at 
any  given  instant  the  less  vascular  part  will  have  in  it  a 
smaller  quantity  of  blood. 

In  the  Circulation  in  the  Capillaries,  as  seen  in  any  trans- 
parent part  of  a  living  adult  animal  by  means  of  the  micro- 
scope (Fig.  52),  the  blood  flows  with  a  constant  equable  motion. 
In  very  young  animals,  the  motion,  though  continuous,  is  ac- 
celerated at  intervals  corresponding  to  the  pulse  in  the  larger 
arteries,  and  a  similar  motion  of  the  blood  is  also  seen  in  the 
capillaries  of  adult  animals  when  they  are  feeble :  if  their 
exhaustion  is  so  great  that  the  power  of  the  heart  is  still  more 
diminished,  the  red  corpuscles  are  observed  to  have  merely 


136 


THE     CIRCULATION. 


FIG.  52. 


Capillaries  in  the  web  of  the  frog's 
foot  magnified. 


the  periodic  motion,  arid  to  remain  stationary  in  the  intervals  ; 
while,  if  the  debility  of  the  animal  is  extreme,  they  even  re- 
cede somewhat  after  each  impulse, 
apparently  because  of  the  elastic- 
ity of  the  capillaries,  and  the  tis- 
sues around  them.  These  obser- 
vations may  be  added  to  those 
already  advanced  (p.  114)  to 
prove  that,  even  in  the  state  of 
great  debility,  the  action  of  the 
heart  is  sufficient  to  impel  the 
blood  through  the  capillary  ves- 
sels. Moreover,  Dr.  Marshall 
Hall  having  placed  the  pectoral 
fin  of  an  eel  in  the  field  of  the 
microscope  and  compressed  it  by 
the  weight  of  a  heavy  probe,  ob- 
served that  the  movement  of  the 
blood  in  the  capillaries  became 
obviously  pulsatory,  the  pulsa- 
tions being  synchronous  with  the  contractions  of  the  ventricle. 
The  pulsatory  motion  of  the  blood  in  the  capillaries  cannot  be 
attributed  to  an  action  in  these  vessels ;  for,  when  the  animal 
is  tranquil,  they  present  not  the  slightest  change  in  their 
diameter. 

It  is  in  the  capillaries,  that  the  chief  resistance  is  offered  to 
the  progress  of  the  blood  ;  for  in  them  the  friction  of  the  blood 
is  greatly  increased  by  the  enormous  multiplication  of  the 
surface  with  which  it  is  brought  in  contact.  The  velocity  of 
the  blood  is  also  in  them  reduced  to  its  minimum,  because  of 
the  widening  of  the  stream.  If,  as  Professor  Miiller  says,  the 
sectional  area  of  all  the  branches  of  a  vessel  united  were 
always  the  same  as  that  of  the  vessel  from  which  they  arise, 
and  if  the  aggregate  sectional  area  of  the  capillary  vessels 
were  equal  to  that  of  the  aorta,  the  mean  rapidity  of  the 
blood's  motion  in  the  capillaries  would  be  the  same  as  in  the 
aorta  and  largest  arteries ;  and  if  a  similar  correspondence  of 
capacity  existed  in  the  veins  and  arteries,  there  would  be  an 
equal  correspondence  in  the  rapidity  of  the  circulation  in  them. 
It  is  quite  true,  that  the  force  with  which  the  blood  is  propelled 
in  the  arteries,  as  shown  by  the  quantity  of  blood  which 
escapes  from  them  in  a  certain  space  of  time,  is  greater  than 
that  with  which  it  moves  in  the  veins ;  but  this  force  has  to 
overcome  all  the  resistance  offered  in  the  arterial  and  capillary 
system — the  heart,  itself,  indeed,  must  overcome  this  resist- 
ance ;  so  that  the  excess  of  the  force  of  the  blood's  motion  in 


THE    CAPILLARIES.  137 

the  arteries  is  expended  in  overcoming  this  resistance,  and  the 
rapidity  of  the  circulation  in  the  arteries,  even  from  the  com- 
mencement of  the  aorta,  would  be  the  same  as  in  the  veins 
and  capillaries,  if  the  aggregate  capacity  of  each  of  the  three 
systems  of  vessels  were  the  same. 

But  since  the  aggregate  sectional  area  of  the  branches  is 
greater  than  that  of  the  trunk  from  which  they  arise,  the 
rapidity  of  the  blood's  motion  will  necessarily  be  greater  in 
the  trunk,  and  will  diminish  in  proportion  as  the  aggregate 
capacity  of  the  vessels  increases  during  their  ramification  :  in 
the  same  manner  as,  other  things  being  equal,  the  velocity  of 
a  stream  diminishes  as  it  widens. 

The  observations  of  Hales,  E.  H.  Weber,  and  Valentin, 
agree  very  closely  as  to  the  rate  of  the  blood  in  the  capillaries 
of  the  frog  ;  and  the  mean  of  their  estimates  gives  the  velocity 
of  the  systemic  capillary  circulation  at  about  one  inch  per 
minute.  Through  the  pulmonic  capillaries,  the  rate  of  motion, 
according  to  Hales,  is  about  five  times  that  through  the  sys- 
temic ones.  The  velocity  in  the  capillaries  of  warm-blooded 
animals  is  greater,  but  has  not  yet  been  accurately  estimated. 
If  it  be  assumed  to  be  three  times  as  great  as  in  the  frog,  still 
the  estimate  may  seem  too  low,  and  inconsistent  with  the  facts, 
which  show  that  the  whole  circulation  is  accomplished  in 
about  a  minute.  But  the  whole  length  of  capillary  vessels, 
through  which  any  given  portion  of  blood  has  to  pass,  prob- 
ably does  not  exceed  -g^th  of  an  inch ;  and  therefore  the  time 
required  for  each  quantity  of  blood  to  traverse  its  own  ap- 
pointed portion  of  the  general  capillary  system  will  scarcely 
amount  to  a  second ;  while  in  the  pulmonic  capillary  system 
the  length  of  time  required  will  be  much  less  even  than  this. 

The  estimates  given  above  are  drawn  from  observations  of 
the  movements  of  the  red  blood-corpuscles,  which  move  in  the 
centre  of  the  stream.  At  the  circumference  of  the  stream,  hi 
contact  with  the  walls  of  the  vessel,  and  adhering  to  them, 
there  is  a  layer  of  liquor  sanguinis  which  appears  to  be  motion- 
less. The  existence  of  this  still  layer,  as  it  js  termed,  is  in- 
ferred both  from  the  general  fact  that  such  a  one  exists  in 
all  fine  tubes  traversed  by  fluid,  and  from  what  can  be  seep  in 
watching  the  movements  of  the  blood-corpuscles.  The  red 
corpuscles  occupy  the  middle  of  the  stream  and  move  with 
comparative  rapidity  ;  the  colorless  lymph-corpusc}es  run  much 
more  slowly  by  the  walls  of  the  vessel ;  while  next  to  the  wall 
there  is  often  a  transparent  space  in  which  the  fluid  appears 
to  be  at  rest ;  for  if  any  of  the  corpuscles  happen  to  be  forced 
within  it,  they  move  more  slowly  than  before,  rolling  lazily 
along  the  side  of  the  vessel,  an4  often  adhering  to  its  wall. 


138  T  H  E    ( ;  I  R  C  U  L  A  T I O  N. 

Part  of  this  slow  movement  of  the  pale  corpuscles  and  their 
occasional  stoppage  may  be  due,  as  E.  H.  Weber  has  suggested, 
to  their  having  a  natural  tendency  to  adhere  to  the  walls  of 
the  vessels.  Sometimes,  indeed,  when  the  motion  of  the  blood 
is  not  strong,  many  of  the  white  corpuscles  collect  in  a  capil- 
lary vessel,  and  for  a  time  entirely  prevent  the  passage  of  the 
red  corpuscles.  But  there  is  no  doubt  that  such  a  still  layer 
of  liquor  sanguinis  exists  next  the  walls  of  the  vessels,  and  it 
is  between  this  and  the  tissues  around  the  vessels  that  those 
interchanges  of  particles  take  place  which  ensue  in  nutrition, 
secretion,  and  absorption  by  the  bloodvessels;  interchanges 
which  are  probably  facilitated  by  the  tranquillity  of  the  fluids 
between  which  they  are  effected. 

Until  within  the  last  few  years  it  has  been  generally  sup- 
posed that  the  occurrence  of  any  transudation  from  the  inte- 
rior of  the  capillaries  into  the  midst  of  the  surrounding  tissues 
was  confined,  in  the  absence  of  injury,  strictly  to  the  fluid  part 
of  the  blood  ;  in  other  words,  that  the  corpuscles  could  not  es- 
cape from  the  circulating  stream,  unless  the  wall  of  the  con- 
taining bloodvessel  were  ruptured.  It  is  true  that  an  English 
physiologist,  Dr.  Augustus  Waller,  affirmed  in  1846,  that  he 
had  seen  blood-corpuscles,  both  red  and  white,  pass  bodily 
through  the  wall  of  the  capillary  vessel  in  which  they  were 
contained ;  and  that,  as  no  opening  could  be  seen  before  their 
escape,  so  none  could  be  observed  afterwards — so  rapidly  was 
the  part  healed.  But  these  observations  did  not  attract  much 
notice  until  the  phenomena  of  escape  of  the  blood-corpuscles 
from  the  capillaries  and  minute  veins,  apart  from  mechanical 
injury,  was  rediscovered  by  Professor  Cohnheim  in  1867. 

Professor  Cohnheim's  experiment  demonstrating  the  passage 
of  the  corpuscles  through  the  wall  of  the  bloodvessel,  is  per- 
formed in  the  following  manner.  A  frog  is  curarized,  that  is 
to  say,  paralysis  is  produced  by  injecting  under  the  skin  a 
minute  quantity  of  the  poison  called  curare;  and  the  abdomen 
having  been  opened,  a  portion  of  small  intestine  is  drawn  out, 
and  its  transparent  mesentery  spread  out  under  a  microscope. 
After  a  variable  time,  occupied  by  dilatation,  following  con- 
traction, of  the  minute  vessels,  and  accompanying  quickening 
of  the  blood-stream,  there  ensues  a  retardation  of  the  current ; 
and  blood-corpuscles,  both  red  and  white,  begin  to  make  their 
way  through  the  capillaries  and  small  veins.  The  process  of 
extrusion  of  the  white  corpuscles  is  thus  described  by  Dr. 
Burdon  Sanderson,  and  the  passage  of  the  red  corpuscles  oc- 
curs after  much  the  same  fashion. 

"Simultaneously  with  the  retardation,  the  leucocytes,  in- 
stead of  loitering  here  and  there  at  the  edge  of  the  axial  cur- 


T  H  E    C  A  P I  L  L  A  K  I E  S.  139 

rent,  begiii_t0  crowd  in  numbers  against  the  vascular  wall,  as 
was  long  ago  described  by  Dr.  Williams.  In  this  way  the 
vein  becomes  lined  with  a  continuous  pavement  of  these  bodies, 
which  remain  almost  motionless,  notwithstanding  that  the 
axial  current  sweeps  by  them  as  continuously  as  before,  though 
with  abated  velocity.  Now  is  the  moment  at  which  the  eye 
must  be  fixed  on  the  outer  contour  of  the  vessel,  from  which 
(to  quote  Professor  Cohnheim's  words)  here  and  there  minute, 
colorless,  button-shaped  elevations  spring,  just  as  if  they  were 
produced  by  budding  out  of  the  wall  of  the  vessel  itself.  The 
buds  increase  gradually  and  slowly  in  size,  until  each  assumes 
the  form  of  a  hemispherical  projection,  of  width  corresponding 
to  that  of  a  leucocyte.  Eventually  the  hemisphere  is  convert- 
ed into  a  pear-shaped  body,  the  small  end  of  which  is  still  at- 
tached to  the  surface  of  the  vein,  while  the  round  part  pro- 
jects freely.  Gradually  the  little  mass  of  protoplasm  removes 
itself  further  and  further  away,  and,  as  it  does  so,  begins  to 
shoot  out  delicate  prongs  of  transparent  protoplasm  from  its 
surface,  in  nowise  differing  in  their  aspect  from  the  slender 
thread  by  which  it  is  still  moored  to  the  vessel.  Finally  the 
thread  is  severed,  and  the  process  is  complete.  The  observer 
has  before  him  an  emigrant  leucocyte,  which  in  all  apprecia- 
ble respects  resembles  those  which  have  been  already  de- 
scribed in  the  aqueous  humor  of  the  inflamed  eye." 

Various  explanations  of  these  remarkable  phenomena  have 
been  suggested.  Probably  the  nearest  to  the  truth  are  those 
which  attribute  the  chief  share  in  the  process  to  the  vital  en- 
dowments with  respect  to  mobility  and  contractility  of  the 
parts  concerned — both  of  the  corpuscles  (Bastian)  and  the  cap- 
illary wall  (Strieker).  Dr.  Sanderson  remarks,  "  The  capillary 
is  not  a  dead  conduit,  but  a  tube  of  living  protoplasm.  There 
is  no  difficulty  in  understanding  how  the  membrane  may  open 
to  allow  the  escape  of  leucocytes,  and  close  again  after  they 
have  passed  out ;  for  it  is  one  of  the  most  striking  peculiari- 
ties of  contractile  substance  that  when  two  parts  of  the  same 
mass  are  separated,  and  again  brought  into  contact,  they  melt 
together  as  if  they  had  not  been  severed." 

Hitherto,  the  escape  of  the  corpuscles  from  the  interior  of 
the  bloodvessels  into  the  surrounding  tissues  has  been  studied 
chiefly  in  connection  with  pathology.  But  it  is  impossible  to 
say,  at  present,  to  what  degree  the  discovery  may  not  influence 
all  present  notions  regarding  the  nutrition  of  the  tissues,  even 
in  health. 

The  circulation  through  the  capillaries  must,  of  necessity, 
be  largely  influenced  by  that  which  occurs  in  the  vessels  on 
either  side  of  them — in  the  arteries  or  the  veins ;  their  in- 


140  THE    CIRCULATION. 

termediate  position  causing  them  to  feel  at  once,  so  to  speak, 
any  alteration  in  the  size  or  rate  of  the  arterial  or  venous 
blood-stream.  Thus,  the  apparent  contraction  of  the  capilla- 
ries, on  the  application  of  certain  irritating  substances,  and 
during  fear,  and  their  dilatation  in  blushing,  may  be  referred 
to  the  action  of  the  small  arteries,  rather  than  to  that  of  the 
capillaries  themselves.  But  largely  as  the  capillaries  are  in- 
fluenced by  these,  and  by  the  conditions  of  the  parts  which 
surround  and  support  them,  their  own  endowments  must  not 
be  disregarded.  They  must  be  looked  upon,  not  as  mere 
passive  canals  for  the  passage  of  blood,  but  as  possessing  en- 
dowments of  their  own,  in  relation  to  the  circulation.  The 
capillary  wall  is,  according  to  Strieker,  actively  living  and 
contractile ;  and  there  is  no  reason  to  doubt  that,  as  such,  it 
must  have  an  important  influence  in  connection  with  that  nu- 
tritive exchange  which  goes  on  without  cessation  between  the 
blood  within  and  the  tissues  outside  the  capillary  vessel ;  a 
process  which,  under  the  name  of  vital  capillary  force,  has 
long  been  recognized  as  one  of  the  means  concerned  in  the 
circulation  of  the  blood. 

The  results  of  morbid  action,  as  well  as  the  phenomena  of 
health,  strongly  support  the  notion  of  the  existence  of  this 
so-called  vital  capillary  attraction  between  the  blood  and  the 
tissues.  For  example,  when  the  access  of  oxygen  to  the  lungs 
is  prevented,  the  circulation  through  the  pulmonic  capillaries 
is  gradually  retarded,  the  blood-corpuscles  cluster  together, 
and  their  movement  is  eventually  almost  arrested,  even  while 
the  action  of  the  heart  continues.  In  inflammation,  also,  the 
capillaries  of  an  inflamed  part  are  enlarged  and  distended 
with  blood,  which  either  moves  very  slowly  or  is  completely 
at  rest.  In  both  these  cases  the  phenomena  are  local,  and  in- 
dependent of  the  action  of  the  heart,  and  appear  to  result 
from  some  alteration  in  the  blood,  which  increases  the  adhesion 
of  its  particles  to  one  another,  and  to  the  walls  of  the  capilla- 
ries, to  an  amount  which  the  propelling  action  of  the  heart  is 
not  able  to  overcome. 

It  may  be  concluded  then,  that  the  capillaries,  which  are 
formed  of  a  simple  cellular  membrane,  can  of  themselves  ex- 
ercise no  such  direct  influence  on  the  movement  of  their  con- 
tents as  to  be  at  all  comparable  in  degree  to  that  which  is  ex- 
ercised by  the  arteries  or  veins :  yet  that  the  constant  inter- 
change of  relations  between  the  blood  within  and  the  tissues 
outside  these  vessels  does  in  some  measure  facilitate  the  move- 
ment of  blood  through  the  capillary  system,  and  constitute  one 
of  the  assistant  forces  of  the  circulation. 


THE     V  E  I  X  S. 


141 


THE   VEINS. 

In  structure  the  coats  of  veins  bear  a  general  resemblance  to 
those  of  arteries.  Thus,  they  possess  an  outer,  middle,  and  in- 
ternal coat.  The  outer  coat  is  constructed  of  areolar  tissue 
like  that  of  the  arteries,  but  is  thicker.  In  some  veins  it  con- 
tains muscular  fibre-cells. 

The  middle  coat  is  considerably  thinuer  than  that  of  the 
arteries ;  and,  although  it  contains  circular  unstriped  muscular 
fibres  or  fibre-cells,  these  are  mingled  with  a  larger  proportion 
of  yellow  elastic  and  white  fibrous  tissue.  In  the  large  veins 
near  the  heart,  namely,  the  vence  eavce  and  pulmonary  veins, 
the  middle  coat  is  replaced,  for  some  distance  from  the  heart, 
by  circularly  arranged  striped  muscular  fibres,  continuous  with 
those  of  the  auricles. 

The  internal  coat  of  veins  is  less  brittle  than  the  correspond- 
ing coat  of  an  artery,  but  in  other  respects  resembles  it  closely. 

The  chief  influence  which  the  veins  have  in  the  circulation, 
is  effected  with  the  help  of  the  valves,  which  are  placed  in  all 
veins  subject  to  local  pressure  from  the  muscles  between  or  near 
which  they  run.  The  general  construction  of  these  valves  is 
similar  to  that  of  the  semiluuar  valves  of  the  aorta  and  pul- 
monary artery,  already  described  (p.  96)  ;  but  their  free  mar- 
gins are  turned  in  the  opposite  direction,  i.e.,  towards  the  heart, 
so  as  to  stop  any  movement  of  blood  backward  in  the  veins. 
They  are  commonly  placed  in  pairs,  at  various  distances  in 
different  veins,  but  almost  uniformly  in  each  (Fig.  53).  In  the 
smaller  veins,  single  valves  are  often  met  with ;  and  three  or 


Diagrams  showing  valves  of  veins.  A.  Part  of  a  vein  laid  open  and  spread  out, 
with  two  pairs  of  valves.  B.  Longitudinal  section  of  a  vein,  showing  the  apposition 
of  the  edges  of  the  valves  in  their  closed  state.  C.  Portion  of  a  distended  vein,  ex- 
hibiting a  swelling  in  the  situation  of  a  pair  of  valves. 


142  THE    CIRCULATION. 

four  are  sometimes  placed  together,  or  near  one  another,  in  the 
largest  veins,  such  as  the  subclavian,  and  at  their  junction  with 
the  jugular  veins.  The  valves  are  semiluuar;  the  unattached 
edge  being  in  some  examples  concave,  in  others  straight.  They 
are  composed  of  inextensile  fibrous  tissue,  and  are  covered 
with  epithelium  like  that  lining  the  veins.  During  the  period 
of  their  inaction,  when  the  venous  blood  is  flowing  in  its  proper 
direction,  they  lie  by  the  sides  of  the  veins ;  but  when  in  ac- 
tion, they  close  together  like  the  valves  of  the  arteries,  and 
offer  a  complete  barrier  to  any  backward  movement  of  the 
blood  (Figs.  54  and  55). 

Valves  are  not  equally  numerous  in  all  veins,  and  in  many 
they  are  absent  altogether.  They  are  most  numerous  in  the 
veins  of  the  extremities,  and  more  so  in  those  of  the  leg  than 
the  arm.  They  are  commonly  absent  in  veins  of  less  than  a 
line  in  diameter,  and,  as  a  general  rule,  there  are  few  or  none 
in  those  which  are  not  subject  to  muscular  pressure.  Among 
those  veins  which  have  no  valves  may  be  mentioned  the  supe- 
rior and  inferior  vena  cava,  the  trunk  and  branches  of  the  portal 
vein,  the  hepatic  and  renal  veins,  and  the  pulmonary  veins ; 
those  in  the  interior  of  the  cranium  and  vertebral  column,  those 
of  the  bones,  and  the  trunk  and  branches  of  the  umbilical  vein 
are  also  destitute  of  valves. 

The  principal  obstacle  to  the  circulation  is  already  over- 
come when  the  blood  has  traversed  the  capillaries;  and  the 
force  of  the  heart  which  is  not  yet  consumed,  is  sufficient  to 
complete  its  passage  through  the  veins,  in  which  the  obstruc- 
tions to  its  movement  are  very  slight.  For  the  formidable 
obstacle  supposed  to  be  presented  by  the  gravitation  of  the 
blood,  has  no  real  existence,  since  the  pressure  exercised  by 
the  column  of  blood  in  the  arteries,  will  be  always  sufficient  to 
support  a  column  of  venous  blood  of  the  same  height  as  itself: 
the  two  columns  mutually  balancing  each  other.  Indeed,  so 
long  as  both  arteries  and  veins  contain  continuous  columns  of 
blood,  the  force  of  gravitation,  whatever  be  the  position  of  the 
body,  can  have  no  power  to  move  or  resist  the  motion  of  any 
part  of  the  blood  in  any  direction.  The  lowest  bloodvessels 
have,  of  course,  to  bear  the  greatest  amount  of  pressure;  the 
pressure  on  each  part  being  directly  proportionate  to  the  height 
of  the  column  of  blood  above  it :  hence  their  liability  to  disten- 
sion. But  this  pressure  bears  equally  on  both  arteries  and 
veins,  and  cannot  either  move,  or  resist  the  motion  of,  the  fluid 
they  contain,  so  long  as  the  columns  of  fluid  are  of  equal 
height  in  both,  and  continuous.  Their  condition  may,  in  this 
respect,  be  compared  with  that  of  a  double  bent  tube,  full  of 
fluid,  held  vertically ;  whatever  be  the  height  and  gravitation 


PRESSURE     IN     VEINS.  143 

of  the  columns  of  fluid,  neither  of  them  can  move  of  its  own 
weight,  each  being  supported  by  the  other ;  yet  the  least  pres- 
sure on  the  top  of  either  column  will  lift  up  the  other ;  so, 
when  the  body  is  erect,  the  least  pressure  on  the  column  of 
arterial  blood  may  lift  up  'the  venous  blood,  and,  were  it  not 
for  the  valves,  the  least  pressure  on  the  venous  might  lift  up 
the  arterial  column. 

In  experiments  to  determine  what  proportion  of  the  force  of 
the  left  ventricle  remains  to  propel  the  blood  in  the  veins,  Valen- 
tin found  that  the  pressure  of  the  blood  in  the  jugular  vein  of 
a  dog,  as  estimated  by  the  hsemadynamometer,  did  not  amount 
to  more  than  j\  or  y1^  of  that  in  the  carotid  artery  of  the  same 
animal ;  and  this  estimate  is  confirmed,  in  the  instances  of 
several  other  arteries  and  their  corresponding  veins,  by  Mogk. 
In  the  upper  part  of  the  inferior  vena  cava,  Valentin  could 
scarcely  detect  the  existence  of  any  pressure,  nearly  the  whole 
force  received  from  the  heart  having  been,  apparently,  con- 
sumed during  the  passage  of  the  blood  through  the  capillaries. 
But  slight  as  this  remaining  force  might  be  (and  the  experi- 
ment in  which  it  was  estimated  would  reduce  the  force  of  the 
heart  below  its  natural  standard),  it  would  be  enough  to  com- 
plete the  circulation  of  the  blood  ;  for,  as  already  stated,  the 
spontaneous  dilatation  of  the  auricles  and  ventricles,  though  it 
may  not  be  forcible  enough  to  assist  the  movement  of  blood 
into  them,  is  adapted  to  offer  to  that  movement  no  obstacle. 

Very  effectual  assistance  to  the  flow  of  blood  in  the  veins 
is  afforded  by  the  action  of  the  muscles  capable  of  pressing  on 
such  veins  as  have  valves. 

The  effect  of  muscular  pressure  on  such  veins  may  be  thus  ex- 
plained. When  pressure  is  applied  to  any  part  of  a  vein,  and 
the  current  of  blood  in  it  is  obstructed,  the  portion  behind  the 
seat  of  pressure  becomes  swollen  and  distended  as  far  back  as 
to  the  next  pair  of  valves.  These,  acting  like  the  arterial 
valves,  and  being,  like  them,  inextensile  both  in  themselves 
and  at  their  margins  of  attachment,  do  not  follow  the  vein  in 
its  distension,  but  are  drawn  out  towards  the  axis  of  the  canal. 
Then,  if  the  pressure  continues  on  the  vein,  the  compressed 
blood,  tending  to  move  equally  in  all  directions,  presses  the 
valves  down  into  contact  at  their  free  edges,  and  they  close  the 
vein  and  prevent  regurgitation  of  the  blood.  Thus,  whatever 
force  is  exercised  by  the  pressure  of  the  muscles  on  the  veins, 
is  distributed  partly  in  pressing  the  blood  onwards  in  the 
proper  course  of  the  circulation,  and  partly  in  pressing  it  back- 
wards and  closing  the  valves  behind. 

The  circulation  might  lose  as  much  as  it  gains  by  such  com- 
pression of  the  veins,  if  it  were  not  for  the  numerous  anas- 


144 


THE     CIRCULATION. 


toraoses  by  which  they  communicate,  one  with  another;  for 
through  these,  the  closing  up  of  the  venous  channel  by  the 
backward  pressure  is  prevented  from  being  any  serious  hin- 
drance to  the  circulation,  since  the  blood,  of  which  the  onward 
course  is  arrested  by  the  closed  valves,  can  at  once  pass 
through  some  anastomosing  channel,  and  proceed  on  its  way 
by  another  vein  (Figs.  54  and  55).  Thus,  therefore,  the 


FIG.  55. 


FIG.  54. — Vein  with  valves  open  (Dalton). 

FIG.  55. — Vein  with  valves  closed  ;  stream  of  blood  passing  off  by  lateral  channel 
(Dalton). 

effect  of  muscular  pressure  upon  veins  which  have  valves,  is 
turned  almost  entirely  to  the  advantage  of  the  circulation  ; 
the  pressure  of  the  blood  onwards  is  all  advantageous,  and 
the  pressure  of  the  blood  backwards  is  prevented  from  being 
a  hindrance  by  the  closure  of  the  valves  and  the  anastomoses 
of  the  veins. 

The  effects  of  such  muscular  pressure  are  well  shown  by 
the  acceleration  of  the  stream  of  blood  when,  in  venesection, 
the  muscles  of  the  forearm  are  put  in  action,  and  by  the 
general  acceleration  of  the  circulation  during  active  exercise ; 
and  the  numerous  movements  which  are  continually  taking 
place  in  the  body  while  awake,  though  their  single  effects  may 
be  less  striking,  must  be  an  important  auxiliary  to  the  venous 
circulation.  Yet  they  are  not  essential ;  for  the  venous  circu- 
lation continues  unimpaired  in  parts  at  rest,  in  paralyzed 
limbs,  and  in  parts  in  which  the  veins  are  not  subject  to  any 
muscular  pressure. 


EFFECTS     OF     RESPIRATION.  145 

Besides  the  assistance  thus  .afforded  by  muscular  pressure 
to  the  movement  of  blood  along  veins  possessed  of  valves,  it 
has  been  discovered  by  Mr.  Wharton  Jones  that,  in  the  web 
of  the  bat's  wing,  the  veins  are  furnished  with  valves,  and 
possess  the  remarkable  property  of  rhythmical  contraction 
and  a  dilatation,  whereby  the  current  of  blood  within  them  is 
distinctly  accelerated.  The  contraction  occurred,  on  an  aver- 
age, about  ten  times  in  a  minute ;  the  existence  of  valves  pre- 
venting regurgitation,  the  entire  effect  of  the  contractions  was 
auxiliary  to  the  onward  current  of  blood.  Analogous  phe- 
nomena have  been  now  frequently  observed  in  other  animals. 

Agents  concerned  in  the  Circulation  of  the  Blood. 

The  agents  concerned  in  the  circulation  of  the  blood  which 
have  been  now  described,  may  be  thus  enumerated  : 

1.  The  action  of  the  heart  and  of  the  arteries. 

2.  The  vital  capillary  force  exercised  in  the  capillaries. 

3.  The  possible  slight  action  of  the  muscular  coat  of  veins ; 
and,  much  more,  the  contraction  of  muscles  capable  of  acting 
on  veins  provided  with  valves. 

It  remains  only  to  consider  (4)  the  influence  of  the  respira- 
tory movements  on  the  circulation. 

Although  the  continuance  of  the  respiratory  movements  is 
essential  to  the  circulation  of  the  blood,  and  although  their 
cessation  is  followed,  within  a  very  few  minutes,  by  that  of  the 
heart's  action  also,  yet  their  direct  mechanical  influence  on  the 
movement  of  the  current  of  blood  is  probably,  under  ordinary 
circumstances,  but  slight.  The  effect  of  expiration  in  increas- 
ing the  pressure  of  the  blood  in  the  arteries  is  minutely  illus- 
trated by  the  experiments  of  Ludwig.  It  acts  as  the  pressure 
of  contracting  muscles  does  upon  the  veins,  and  is  advantage- 
ous to  the  onward  movement  of  arterial  blood,  inasmuch  as  all 
movement  backwards  into  the  heart,  which  would  otherwise 
occur  at  the  same  moment  and  from  the  same  cause,  is  pre- 
vented by  the  force  of  the  onward  stream  of  blood  from  the 
contracting  ventricle,  and  in  the  intervals  of  this  contraction 
by  the  closure  of  the  semilunar  valves.  Under  ordinary  cir- 
cumstances, and  with  a  free  passage  through  the  capillaries  of 
the  lungs,  the  effect  of  expiration  on  the  stream  of  blood  in  the 
veins  is  also  probably  to  assist,  rather  than  retard  its  move- 
ment in  the  proper  direction.  For,  with  no  obstruction  in 
front,  there  is  the  force  of  the  blood  streaming  into  the  heart 
from  behind,  to  prevent  any  tendency  to  a  backward  flow,  even 
apart  from  what  may  be  effected  by  the  presence  of  the  valves 
of  the  venous  system. 


146  THE     CIRCULATION. 

It  is  true  that  in  violent  expiratory  efforts  there  is  a  certain 
retardation  of  the  circulation  in  the  veins.  The  effect  of  such 
retardation  is  shown  in  the  swelling  up  of  the  veins  of  the  head 
and  neck,  and  the  lividity  of  the  face,  during  coughing,  strain- 
ing, and  similar  violent  expiratory  efforts ;  the  effect  shown  in 
these  instances  being  due  both  to  some  actual  regurgitation  of 
the  blood  in  the  great  veins,  and  to  the  accumulation  of  blood 
in  all  the  veins,  from  their  being  constantly  more  and  more 
filled  by  the  influx  from  the  arteries. 

But  strong  expiratory  efforts,  as  in  straining  and  the  like, 
are  not  fairly  comparable  to  ordinary  expiration,  inasmuch  as 
they  are  instances  of  more  or  less  interference  with  expiration, 
and  involve  probably  circumstances  leading  to  obstruction  of 
the  circulation  in  the  pulmonary  capillaries,  such  as  are  not 
present  in  the  ordinary  rhythmical  exit  of  air  from  the  lungs. 

The  act  of  inspiration  is  favorable  to  the  venous  circulation, 
and  its  effect  is  not  counterbalanced  by  its  tendency  to  draw 
the  arterial,  as  well  as  the  venous,  blood  towards  the  cavity  of 
the  chest.  When  the  chest  is  enlarged  in  inspiration,  the  ad- 
ditional space  within  it  is  filled  chiefly  by  the  fresh  quantity 
of  air  which  passes  through  the  trachea  and  bronchial  passages 
to  the  vesicular  structure  of  the  lungs.  But  the  blood  being, 
like  the  air,  subject  to  the  atmospheric  pressure,  some  of  it  also 
is  at  the  same  time  pressed  towards  the  expanding  cavity  of 
the  chest,  and  therein  towards  the  heart.  The  effect  of  this  on 
the  arterial  current  is  hindered  by  the  aortic  valves,  while  they 
are  closed,  and  by  the  forcible  outward  stream  of  blood  from 
the  ventricles  when  they  are  open  ;  while,  on  the  other  hand, 
there  is  nothing  to  prevent  an  increased  afflux  of  blood  to  the 
auricles  through  the  large  veins. 

Sir  David  Barry  was  the  first  who  showed  plainly  this  effect 
of  inspiration  on  the  venous  circulation ;  and  he  mentions 
the  following  experiment  in  proof  of  it.  He  introduced  one 
end  of  a  bent  glass  tube  into  the  jugular  vein  of  an  animal, 
the  vein  being  tied  above  the  point  where  the  tube  was  in- 
serted ;  the  inferior  end  of  the  tube  was  immersed  in  some 
colored  fluid.  He  then  observed  that  at  the  time  of  each  in- 
spiration the  fluid  ascended  in  the  tube,  while  during  expiration 
it  either  remained  stationary,  or  even  sank.  Poiseuille  con- 
firmed the  truth  of  this  observation,  in  a  more  accurate  manner, 
by  means  of  his  haemadynamometer.  And  a  like  confirmation 
has  been  since  furnished  by  Valentin,  and  in  minute  details 
by  Ludwig. 

The  effect  of  inspiration  on  the  veins  is  observable  only  in 
the  large  ones  near  the  thorax.  Poiseuille  could  not  detect  it 
by  means  of  his  instrument  in  veins  more  distant  from  the 


VELOCITY    OF     THE  •'"CIBCUL ATION.  147 

heart — for  example,  in  the  veins  of  the  extremities.  And  its 
beneficial  effect  would  be  neutralized  were  it  not  for  the  valves  ; 
for  he  found  that,  when  he  repeated  Sir  D.  Barry's  exper- 
iments, and  passed  the  tube  so  far  along  the  veins  that  it  went 
beyond  the  valves  nearest  to  the  heart,  as  much  fluid  was  forced 
back  into  the  tube  in  every  expiration  as  was  drawn  in  through 
it  in  every  inspiration. 

Some  recent  experiments,  by  Dr.  Burdon  Sanderson,  have 
proved  more  directly  that  inspiration  is  favorable  to  the  cir- 
culation, inasmuch  as,  during  it,  the  tension  of  the  arterial 
system  is  increased.  And  it  is  only  when  the  respiratory  orifice 
is  closed,  as  by  plugging  the  trachea,  that  inspiratory  efforts 
are  sufficient  to  produce  an  opposite  effect — to  diminish  the 
tension  in  the  arteries. 

On  the  whole,  therefore,  the  respiratory  movements  of  the 
chest  are  advantageous  to  the  circulation. 

Velocity  of  Blood  in  the  Veins. 

The  velocity  of  the  blood  is  greater  in  the  veins  than  in  the 
capillaries,  but  less  than  in  the  arteries ;  and  with  this  fact 
may  be  remembered  the  relative  capacities  of  the  arterial  and 
venous  systems ;  for  since  the  veins  return  to  the  heart  all  the 
blood  that  they  receive  from  it  in  a  given  time  through  the 
arteries,  their  larger  size  and  proportionally  greater  number 
must  compensate  for  the  slower  movement  of  the  blood  through 
them.  If  an  accurate  estimate  of  the  proportionate  areas  of 
arteries  and  the  veins  corresponding  to  them  could  be  made, 
we  might,  from  the  velocity  of  the  arterial  current,  calculate 
that  of  the  venous.  A  usual  estimate  is,  that  the  capacity 
of  the  veins  is  about  twice  or  three  times  as  great  as  that  of 
the  arteries,  and  that  the  velocity  of  the  blood's  motion  is, 
therefore,  about  twice  or  three  times  as  great  in  the  arteries  as 
in  the  veins.  Some  doubt  has,  however,  been  lately  expressed 
regarding  the  accuracy  of  this  calculation,  and  the  matter, 
therefore,  must  be  considered  not  yet  settled.  The  rate  at 
which  the  blood  moves  in  the  veins  gradually  increases  the 
nearer  it  approaches  the  heart,  for  the  sectional  area  of  the 
venous  trunks,  compared  with  that  of  the  branches  opening 
into  them,  becomes  gradually  less  as  the  trunks  advance  to- 
wards the  heart. 

Velocity  of  the  Circulation. 

Having  now  considered  the  share  which  each  of  the  circu- 
latory organs  has  in  the  propulsion  and  direction  of  the  blood, 
we  may  speak  of  their  combined  effects,  especially  in  regard  to 


148  THE    CIRCULATION. 

the  velocity  with  which  the  movement  of  the  blood  through  the 
whole  round  of  the  circulation  is  accomplished.  As  Miiller 
says,  the  rate  of  the  blood's  motion  in  the  vessels  must  not  be 
judged  of  by  the  rapidity  with  which  it  flows  from  a  vessel 
when  divided.  In  the  latter  case,  the  rate  of  motion  is  the 
result  of  the  entire  pressure  to  which  the  whole  mass  of  blood 
is  subjected  in  the  vascular  system,  and  which  at  the  point  of 
the  incision  in  the  vessel  meets  with  no  resistance.  In  the 
closed  vessels,  on  the  contrary,  no  portion  of  blood  can  be 
moved  forwards  except  by  impelling  on  the  whole  mass,  and 
by  overcoming  the  resistance  arising  from  friction  in  the 
smaller  vessels. 

From  the  rate  at  which  the  blood  escapes  from  opened  ves- 
sels we  can  only  judge,  in  general,  that  its  velocity  is,  as 
already  said,  greater  in  arteries  than  in  veins,  and  in  both 
these  greater  than  in  the  capillaries.  More  satisfactory  data 
for  the  estimates  are  afforded  by  the  results  of  experiments  to 
ascertain  the  rapidity  with  which  poisons  introduced  into  the 
blood  are  transmitted  from  one  part  of  the  vascular  system  to 
another.  From  eighteen  such  experiments  on  horses,  Hering 
deduced  that  the  time  required  for  the  passage  of  a  solution  of 
ferrocyanide  of  potassium,  mixed  with  the  blood,  from  one 
jugular  vein  (through  the  right  side  of  the  heart,  the  pulmon- 
ary circulation,  the  left  cavities  of  the  heart,  and  the  general 
circulation)  to  the  jugular  vein  of  the  opposite  side,  varies 
from  twenty  to  thirty  seconds.  The  same  substance  was  trans- 
mitted from  the  jugular  vein  to  the  great  saphena  in  twenty 
seconds;  from  the  jugular  vein  to  the  masseteric  artery,  in 
between  fifteen  and  thirty  seconds  ;  to  the  facial  artery,  in  one 
experiment,  in  between  ten  and  fifteen  seconds ;  in  another 
experiment,  in  between  twenty  and  twenty-five  seconds ;  in  its 
transit  from  the  jugular  vein  to  the  metatarsal  artery,  it  occu- 
pied between  twenty  and  thirty  seconds,  and  in  one  instance 
more  than  forty  seconds.  The  result  was  nearly  the  same 
whatever  was  the  rate  of  the  heart's  action. 

Poiseuille's  observations  accord  completely  with  the  above, 
and  show,  moreover,  that  when  the  ferrocyanide  is  injected 
into  the  blood  with  other  substances,  such  as  acetate  of  am- 
monia, or  nitrate  of  potash  (solutions  of  which,  as  other 
experiments  have  shown,  pass  quickly  through  capillary- 
tubes),  the  passage  from  one  jugular  vein  to  the  other  is  ef- 
fected in  from  eighteen  to  twenty -four  seconds  ;  while,  if  instead 
of  these,  alcohol  is  added,  the  passage  is  not  completed  until 
from  forty  to  forty-five  seconds  after  injection.  Still  greater 
rapidity  of  transit  has  been  observed  by  Mr.  J.  Blake,  who 
found  that  nitrate  of  baryta  injected  into  the  jugular  vein  of 


VELOCITY    OF    THE    CIRCULATION.  149 

a  horse  could  be  detected  in  blood  drawn  from  the  carotid  ar- 
tery of  the  opposite  side  in  from  fifteen  to  twenty  seconds  after 
the  injection.  In  sixteen  seconds  a  solution  of  nitrate  of 
potash,  injected  into  the  jugular  vein  of  a  horse,  caused  com- 
plete arrest  of  the  heart's  action,  by  entering  and  diffusing 
itself  through  the  coronary  arteries.  In  a  dog,  the  poisonous 
effects  of  strychnia  on  the  nervous  system  were  manifested  in 
twelve  seconds  after  injection  into  the  jugular  vein;  in  a  fowl, 
in  six  and  a  half  seconds,  and  in  a  rabbit  in  four  and  a  half 
seconds. 

In  all  these  experiments,  it  is  assumed  that  the  substance 
injected  moves  with  the  blood,  and  at  the  same  rate  as  it,  and 
does  not  move  from  one  part  of  the  organs  of  circulation  to 
another  by  diffusing  itself  through  the  blood  or  tissues  more 
quickly  than  the  blood  moves.  The  assumption  is  sufficiently 
probable,  to  be  considered  nearly  certain,  that  the  times  above- 
mentioned,  as  occupied  in  the  passage  of  the  injected  sub- 
stances, are  those  in  which  the  portion  of  blood,  into  which 
each  was  injected,  was  carried  from  one  part  to  another  of  the 
vascular  system.  It  would,  therefore,  appear  that  a  portion  of 
blood  can  traverse  the  entire  course  of  the  circulation,  in  the 
horse,  in  half  a  minute ;  of  course  it  would  require  longer  to 
traverse  the  vessels  of  the  most  distant  part  of  the  extremities 
than  to  go  through  those  of  the  neck  ;  but  taking  an  average 
length  of  vessels  to  be  traversed,  and  assuming,  as  we  may, 
that  the  movement  of  blood  in  the  human  subject,  is  not 
slower  than  in  the  horse,  it  may  be  concluded  that  one  minute, 
which  is  the  estimate  usually  adopted  of  the  average  time  in 
which  the  blood  completes  its  entire  circuit  in  man,  is  rather 
above  than  below  the  actual  rate. 

Another  jnocle  of  estimating  the  general  velocity  of  the  cir- 
culating blood,  is  by  calculating  it  from  the  quantity  of  blood 
supposed  to  be  contained  in  the  body,  and  from  the  quantity 
which  can  pass  through  the  heart  in  each  of  its  actions.  But 
the  conclusions  arrived  at  by  this  method  are  less  satisfactory. 
For  the  estimates,  both  of  the  total  quantity  of  blood,  and  of 
the  capacity  of  the  cavities  of  the  heart,  have  as  yet  only  ap- 
proximated to  the  truth.  Still,  the  most  careful  of  the  esti- 
mates thus  made  accord  with  those  already  mentioned ;  for 
Valentin  has,  from  these  data,  calculated  that  the  blood  may 
all  pass  through  the  heart  in  from  43  j  to  62f  seconds. 

The  estimate  for  the  speed  at  which  the  blood  may  be  seen 
moving  in  transparent  parts,  is  not  opposed  to  this.  For,  as 
already  stated  (p.  137),  though  the  movement  through  the 
capillaries  may  be  very  slow,  yet  the  length  of  capillary  vessel 
through  which  any  portion  of  blood  has  to  pass  is  very  small. 

13 


150  THE    CIRCULATION. 

Even  if  we  estimate  that  length  at  the  tenth  of  an  inch,  and 
suppose  the  velocity  of  the  blood  therein  to  be  only  one  inch 
per  minute,  then  each  portion  of  blood  may  traverse  its  own 
distance  of  the  capillary  system  in  about  six  seconds.  There 
would  thus  be  plenty  of  time  for  the  blood  to  travel  through 
its  circuit  in  the  larger  vessels,  in  which  the  greatest  length  of 
tube  that  it  can  have  to  traverse  in  the  human  subject  does 
not  exceed  ten  feet. 

All  the  estimates  here  given  are  averages ;  but  of  course  the 
time  in  which  a  given  portion  of  blood  passes  from  one  side  of 
the  heart  to  the  other,  varies  much  according  to  the  organ  it 
has  to  traverse.  The  blood  which  circulates  from  the  left  ven- 
tricle, through  the  coronary  vessels,  to  the  right  side  of  the 
heart,  requires  a  far  shorter  time  for  the  completion  of  its 
course  than  the  blood  which  flows  from  the  left  side  of  the 
heart  to  the  feet,  and  back  again  to  the  right  side  of  the  heart ; 
for  the  circulation  from  the  left  to  the  right  cavities  of  the 
heart  may  be  represented  as  forming  a  number  of  arches,  vary- 
ing in  size,  and  requiring  proportionately  various  times  for  the 
blood  to  traverse  them;  the  smallest  of  these  arches  being 
formed  by  the  circulation  through  the  coronary  vessels  of  the 
heart  itself.  The  course  of  the  blood  from  the  right  side  of 
the  heart,  through  the  lungs  to  the  left,  is  shorter  than  most 
of  the  arches  described  by  the  systemic  circulation,  and  in  it 
the  blood  flows,  cceteris  paribus,  much  quicker  than  in  most  of 
the  vessels  which  belong  to  the  aortic  circulation.  For  although 
the  quantity  of  blood  contained,  at  any  instant,  in  the  greater 
circulation  of  the  body,  is  far  greater  than  the  quantity  within 
the  lesser  circulation ;  yet,  in  any  given  space  of  time,  as  much 
blood  must  pass  through  the  lungs  as  passes  in  the  same 
time  through  the  systemic  circulation.  If  the  systemic  vessels 
contain  five  times  as  much  blood  as  the  pulmonary,  the  blood 
in  them  must  move  five  times  as  slow  as  in  these;  else,  the 
right  side  of  the  heart  would  be  either  overfilled  or  not  filled 
enough. 

Peculiarities  of  the  Circulation  in  different  Parts. 

The  most  remarkable  peculiarities  attending  the  circulation 
of  blood  through  different  organs  are  observed  in  the  cases  of 
the  lungs,  the  liver,  the  brain,  and  the  erectile  organs.  The 
pulmonary  and  portal  circulations  have  been  already  alluded 
to  (pp.  89,  90),  and  will  be  again  noticed  when  considering 
the  functions  of  the  lungs  and  liver. 

The  chief  circumstances  requiring  notice,  in  relation  to  the 
cerebral  circulation,  are  observed  in  the  arrangement  and  dis- 


CEREBRAL    CIRCULATION.  151 

tribution  of  the  vessels  of  the  brain,  and  in  the  conditions 
attending  the  amount  of  blood  usually  contained  within  the 
cranium. 

The  functions  of  the  brain  seem  to  require  that  it  should 
receive  a  large  supply  of  blood.  This  is  accomplished  through 
the  number  and  size  of  its  arteries,  the  two  internal  carotids, 
and  the  two  vertebrals.  But  it  appears  to  be  further  necessary 
that  the  force  with  which  this  blood  is  sent  to  the  brain  should 
be  less,  or  at  least,  subject  to  less  variation  from  external  cir- 
cumstances than  it  is  in  other  parts.  This  object  is  effected  by 
several  provisions;  such  as  the  tortuosity  of  the  large  arteries, 
and  their  wide  anastomoses  in  the  formation  of  the  circle  of  Wil- 
lis, which  will  insure  that  the  supply  of  blood  to  the  brain  maybe 
uniform,  though  it  may  by  an  accident  be  diminished,  or  in  some 
way  changed,  through  one  or  more  of  the  principal  arteries. 
The  transit  of  the  large  arteries  through  bone,  especially  the 
carotid  canal  of  the  temporal  bone,  may  prevent  any  undue 
distension;  and  uniformity  of  supply  is  further  insured  by  the 
arrangement  of  the  vessels  in  the  pia  mater,  in  which,  previous 
to  their  distribution  to  the  substance  of  the  brain,  the  large 
arteries  break  up  and  divide  into  innumerable  minute  branches 
ending  in  capillaries,  which,  after  frequent  communications 
with  one  another,  enter  the  brain,  and  carry  into  nearly  every 
part  of  it  uniform  and  equable  streams  of  blood. 

The  arrangement  of  the  veins  within  the  cranium  is  also  pe- 
culiar. The  large  venous  trunks  or  sinuses  are  formed  so  as 
to  be  scarcely  capable  of  change  of  size;  and  composed,  as 
they  are,  of  the  tough  tissue  of  the  dura  mater,  and,  in  some 
instances,  bounded  on  one  side  by  the  bony  cranium,  they  are 
not  compressible  by  any  force  which  the  fulness  of  the  arteries 
might  exercise  through  the  substance  of  the  brain  ;  nor  do  they 
admit  of  distension  when  the  flow  of  venous  blood  from  the 
brain  is  obstructed. 

The  general  uniformity  in  the  supply  of  blood  to  the  brain, 
which  is  thus  secured,  is  well  adapted,  not  only  to  its  functions, 
but  also  to  its  condition  as  a  mass  of  nearly  incompressible 
substance  placed  in  a  cavity  with  unyielding  walls.  These 
conditions  of  the  brain  and  skull  have  appeared,  indeed,  to 
some,  enough  to  justify  the  opinion  that  the  quantity  of  blood  in 
the  brain  must  be  at  all  times  the  same  ;  and  that  the  quantity  of 
blood  received  within  any  given  time  through  the  arteries  must 
be  always,  and  at  the  same  time,  exactly  equal  to  that  re- 
moved by  the  veins.  In  accordance  with  this  supposition,  the 
symptoms  commonly  referred  to  either  excess  or  deficiency  of 
blood  in  the  brain,  were  ascribed  to  a  disturbance  in  the  bal- 
ance between  the  quantity  of  arterial  and  that  of  venous  blood. 


152  THE    CIRCULATION. 

Some  experiments  performed  by  Dr.  Kellie  appeared  to  estab- 
lish the  correctness  of  this  view.  But  Dr.  Burrows  having 
repeated  these  experiments,  and  performed  additional  ones, 
obtained  different  results.  He  found  that  in  animals  bled  to 
death,  without  any  aperture  being  made  in  the  cranium,  the 
brain  became  pale  and  anaemic  like  other  parts.  And  in  proof 
that,  during  life,  the  cerebral  circulation  is  influenced  by 
the  same  general  circumstances  that  influence  the  circulation 
elsewhere,  he  found  congestion  of  the  cerebral  vessels  in  rab- 
bits killed  by  strangling  or  drowning  ;  while  in  others,  killed 
by  prussic  acid,  he  observed  that  the  quantity  of  blood  in  the 
cavity  of  the  cranium  was  determined  by  the  position  in  which 
the  animal  was  placed  after  death,  the  cerebral  vessels  being 
congested  when  the  animal  was  suspended  with  his  head  down- 
wards, and  comparatively  empty  when  the  animal  was  kept 
suspended  by  the  ears.  He  concluded,  therefore,  that  although 
the  total  volume  of  the  contents  of  the  cranium  is  probably 
nearly  always  the  same,  yet  the  quantity  of  blood  in  it  is  liable 
to  variation,  its  increase  or  diminution  being  accompanied  by 
a  simultaneous  diminution  or  increase  in  the  quantity  of  the 
cerebro-spinal  fluid,  which,  by  readily  admitting  of  being  re- 
moved from  one  part  of  the  brain  and  spinal  cord  to  another, 
and  of  being  rapidly  absorbed,  and  as  readily  effused,  would 
serve  as  a  kind  of  supplemental  fluid  to  the  other  contents  of 
the  cranium,  to  keep  it  uniformly  filled  in  case  of  variations 
in  their  quantity.  And  there  can  be  no  doubt  that,  although 
the  arrangements  of  the  bloodvessels,  to  which  reference  has 
been  made,  insure  to  the  brain  an  amount  of  blood  which  is 
tolerably  uniform,  yet,  inasmuch  as  with  every  beat  of  the 
heart  and  every  act  of  respiration,  and  under  many  other  cir- 
cumstances, the  quantity  of  blood  in  the  cavity  of  the  cranium 
is  constantly  varying,  it  is  plain  that,  were  there  not  provision 
made  for  the  possible  displacement  of  some  of  the  contents  of 
the  unyielding  bony  case  in  which  the  brain  is  contained,  there 
would  be  often  alternations  of  excessive  pressure  with  insuffi- 
cient supply  of  blood.  Hence  we  may  consider  that  the  cere- 
bro-spinal fluid  in  the  interior  of  the  skull  not  only  subserves 
the  mechanical  functions  of  fat  in  other  parts  as  a  packing 
material,  but  by  the  readiness  with  which  it  can  be  displaced 
into  the  spinal  canal,  provides  the  means  whereby  undue  pres- 
sure and  insufficient  supply  of  blood  are  equally  prevented. 

Circulation  in  Erectile  Structures. — The  instances  of  greatest 
variation  in  the  quantity  of  blood  contained,  at  different  times, 
in  the  same  organs,  are  found  in  certain  structures  which, 
under  ordinary  circumstances,  are  soft  and  flaccid,  but,  at  cer- 
tain times,  receive  an  unusually  large  quantity  of  blood,  be- 


CIRCULATION   IN    ERECTILE   STRUCTURES.      153 

come  distended  and  swollen  by  it,  and  pass  into  the  state 
which  has  been  termed  erection.  Such  structures  are  the  cor- 
pora cavernosa  and  corpus  spongiosum  of  the  penis  in  the 
male,  and  the  clitoris  in  the  female;  and,  to  a  less  degree,  the 
nipple  of  the  mammary  gland  in  both  sexes.  The  corpus 
cavernosum  penis,  which  is  the  best  example  of  an  erectile 
structure,  has  an  external  fibrous  membrane  or  sheath ;  and 
from  the  inner  surface  of  the  latter  are  prolonged  numerous 
fine  lamellse  which  divide  its  cavity  into  small  compartments 
looking  like  cells  when  they  are  inflated.  Within  these  is 
situated  the  plexus  of  veins  upon  which  the  peculiar  erectile 
property  of  the  organ  mainly  depends.  It  consists  of  short 
veins  which  very  closely  interlace  and  anastomose  with  each 
other  in  all  directions,  and  admit  of  great  variation  of  size, 
collapsing  in  the  passive  state  of  the  organ,  but,  for  erection, 
capable  of  an  amount  of  dilatation  which  exceeds  beyond 
comparison  that  of  the  arteries  and  veins  which  convey  the 
blood  to  and  from  them.  The  strong  fibrous  tissue  lying  in 
the  intervals  of  the  venous  plexuses,  and  the  external  fibrous 
membrane  or  sheath  with  which  it  is  connected,  limit  the  dis- 
tension of  the  vessels,  and,  during  the  state  of  erection,  give  to 
the  penis  its  condition  of  tension  and  firmness.  The  same 
general  condition  of  vessels  exists  in  the  corpus  spongiosum 
urethrse,  but  around  the  urethra  the  fibrous  tissue  is  much 
weaker  than  around  the  body  of  the  penis,  and  around  the 
glans  there  is  none.  The  venous  blood  is  returned  from  the 
plexuses  by  comparatively  small  veins ;  those  from  the  glans 
and  the  fore  part  of  the  urethra  empty  themselves  into  the 
dorsal  vein  of  the  penis ;  those  from  the  corpus  cavernosum 
pass  into  deeper  veins  which  issue  from  the  corpora  cavernosa 
at  the  crura  penis ;  and  those  from  the  rest  of  the  urethra  and 
bulb  pass  more  directly  into  the  plexus  of  the  veins  about  the 
prostate.  For  all  these  veins  one  condition  is  the  same ; 
namely,  that  they  are  liable  to  the  pressure  of  muscles  when 
they  leave  the  penis.  The  muscles  chiefly  concerned  in  this 
action  are  the  erector  penis  and  accelerator  urinse. 

Erection  results  from  the  distension  of  the  venous  plexuses 
with  blood.  The  principal  exciting  cause  in  the  erection  of 
the  penis  is  nervous  irritation,  originating  in  the  part  itself,  or 
derived  from  the  brain  and  spinal  cord.  The  nervous  in- 
fluence is  communicated  to  the  penis  by  the  pudic  nerves, 
which  ramify  in  its  vascular  tissue:  and  Guenther  has  ob- 
served, that,  after  their  division  in  the  horse,  the  penis  is  no 
longer  capable  of  erection.  It  affords  a  good  example  of  the 
subjection  of  the  circulation  in  an  individual  organ  to  the 


154  THE    CIRCULATION. 

influence  of  the  nerves ;  but  the  mode  in  which  they  excite  a 
greater  influx  of  blood  is  not  with  certainty  known. 

The  most  probable  explanation  is  that  offered  by  Professor 
Kolliker,  who  ascribes  the  distension  of  the  venous  plexuses  to 
the  influence  of  organic  muscular  fibres,  which  are  found  in 
abundance  in  the  corpora  cavernosa  of  the  penis,  from  the 
bulb  to  the  glans,  also  in  the  clitoris  and  other  parts  capable 
of  erection.  While  erectile  organs  are  flaccid  and  at  rest, 
these  contractile  fibres  exercise  an  amount  of  pressure  on  the 
plexuses  of  vessels  distributed  amongst  them,  sufficient  to  pre- 
vent their  distension  with  blood.  But  when  through  the  in- 
fluence of  their  nerves,  these  parts  are  stimulated  to  erection, 
the  action  of  these  fibres  is  suspended,  and  the  plexuses  thus 
liberated  from  pressure,  yield  to  the  distending  force  of  the 
blood,  which,  probably,  at  the  same  time  arrives  in  greater 
quantity,  owing  to  a  simultaneous  dilatation  of  the  arteries  of 
the  parts,  and  thus  the  plexuses  become  filled,  and  remain  so 
until  the  stimulus  to  erection  subsides,  when  the  organic  mus- 
cular fibres  again  contract,  and  so  gradually  expel  the  excess 
of  blood  from  the  previously  distended  vessels.  The  influence 
of  cold  in  producing  extreme  contraction  and  shrinking  of 
erectile  organs,  and  the  opposite  effect  of  warmth  in  inducing 
fulness  and  distension  of  these  parts,  are  among  the  arguments 
used  by  Kolliker  in  support  of  this  opinion. 

The  accurate  dissections  and  experiments  of  Kobelt,  extend- 
ing and  confirming  those  of  Le  Gros  Clark  and  Krause,  have 
shown,  that  this  influx  of  the  blood,  however  explained,  is 
the  first  condition  necessary  for  erection,  and  that  through 
it  alone  much  enlargement  and  turgescence  of  the  penis  may 
ensue.  But  the  erection  is  probably  not  complete,  nor  main- 
tained for  any  time  except  when,  together  with  this  influx,  the 
muscles  already  mentioned  contract,  and  by  compressing  the 
veins,  stop  the  efflux  of  blood,  or  prevent  it  from  being  as  great 
as  the  influx. 

It  appears  to  be  only  the  most  perfect  kind  of  erection  that 
needs  the  help  of  muscles  to  compress  the  veins ;  and  none 
such  can  materially  assist  the  erection  of  the  nipples,  or  that 
amount  of  turgescence,  just  falling  short  of  erection,  of  which 
the  spleen  and  many  other  parts  are  capable.  For  such  tur- 
gescence nothing  more  seems  necessary  than  a  large  plexiform 
arrangement  of  the  veins,  and  such  arteries  as  may  admit, 
upon  local  occasions,  augmented  quantities  of  blood. 

The  Influence  of  the  Nervous  System  on  the  circulation  in 
the  bloodvessels  will  be  considered  in  Chapter  XVII. 


STRUCTURE    OF    THE    LUNGS.  155 


CHAPTER  VII. 

RESPIRATION. 

As  the  blood  circulates  through  the  various  parts  of  the 
body,  and  fulfils  its  office  by  nourishing  the  several  tissues,  by 
supplying  to  secreting  organs  the  materials  necessary  for  their 
secretions,  and  by  the  performance  of  other  duties  with  which 
it  is  charged,  it  is  deprived  of  part  of  its  nutritive  constituents, 
and  receives  impurities  which  need  removal  from  the  body.  It 
is,  therefore,  necessary  that  fresh  supplies  of  nutriment  should 
be  continually  added  to  the  blood,  and  that  provision  should 
be  made  for  the  removal  of  the  impurities.  The  first  of  these 
objects  is  accomplished  by  the  processes  of  digestion  and  ab- 
sorption. The  second  is  principally  effected  by  the  agency  of 
the  various  excretory  organs,  through  which  are  removed  the 
several  impurities  with  which  the  blood  is  charged,  whether 
these  impurities  are  derived  altogether  from  the  degenerations 
of  tissue,  or  in  part  also  from  the  elements  of  unassimilated 
food.  One  of  the  most  important  and  abundant  of  the  impu- 
rities is  carbonic  acid,  the  removal  of  which  and  the  introduc- 
tion of  fresh  quantities  of  oxygen,  constitute  the  chief  purpose 
of  respiration — a  process  which,  because  of  its  intimate  rela- 
tion to  the  circulation,  may  be  considered  here,  rather  than 
with  the  other  excretory  functions. 

Position  and  Structure  of  the  Lungs. 

The  lungs  occupy  the  greater  portion  of  the  chest,  or  upper- 
most of  the  two  cavities  into  which  the  body  is  divided  by  the 
diaphragm  (Fig.  31).  They  are  of  a  spongy  elastic  texture, 
and  on  section  appear  to  the  naked  eye  as  if  they  were  in 
great  part  solid  organs,  except  here  and  there,  at  certain 
points,  where  branches  of  the  bronchi  or  air-tubes  may  have 
been  cut  across,  and  show,  on  their  surface  of  the  section,  their 
tubular  structure. 

In  fact,  however,  the  lungs  are  hollow  organs,  and  we  may 
consider  them  as  really  two  bags  containing  air,  each  of  which 
communicates  by  a  separate  orifice  with  a  common  air-tube 
(Fig.  31 ),  through  the  upper  portion  of  which,  the  larynx,  they 
freely  communicate  with  the  external  atmosphere.  The  orifice 


156  RESPIRATION. 

of  the  larynx  is  guarded  by  muscles,  and  can  be  opened  or 
closed  at  will. 

It  has  been  said,  in  the  preceding  chapter  that  each  lung 
is  enveloped  in  a  distinct  fibrous  bag,  with  a  smooth,  slippery 
lining,  and  that  the  outer  smooth  surface  of  the  lung  glides 
easily  on  the  inner  smooth  surface  of  the  bag  which  envelops 

FIG.  56. 


Transverse  section  of  the  chest  (after  Gray). 

it.  This  enveloping  bag,  which  is  called  the  pleura,  is  easily 
seen  in  the  dead  subject ;  and  when  it  is  opened,  as  in  an  ordi- 
nary post-mortem  examination,  there  is  a  considerable  space 
left,  by  the  elastic  recoil  of  the  lung,  between  the  outer  sur- 
face of  the  lung  and  the  inner  surface  of  the  pleura,  which  is 
left  sticking,  so  to  speak,  to  the  inner  surface  of  the  walls  and 
floor  of  the  chest. 

The  space,  however,  between  the  lung  and  the  pleura  does 
not  exist  (except  in  some  cases  of  disease)  so  long  as  the  chest 
is  not  opened ;  and,  while  considering  the  subject  of  normal 
healthy  respiration,  we  may  discard  altogether  the  notion  of 
any  space  or  cavity  between  the  lung  and  the  wall  of  the 
chest.  So  far  as  the  movement  of  the  lung  is  concerned  it 
might  be  adherent  completely  to  the  chest-wall,  inasmuch  as 
they  accompany  each  other  in  all  their  movements ;  only  there 
is  a  slight  gliding  of  the  smooth  surface  of  the  lung  on  the 
smooth  inner  surface  of  the  pleura,  but  no  separation,  in  the 
slightest  degree,  of  one  from  the  other.1 

1  It  may  be  mentioned,  that  the  smooth  covering  of  the  lung  is 
really  continuous  with  the  inner  smooth  lining  of  the  walls  arid 
floor  of  the  chost,  as  will  be  readily  seen  in  Fig.  56.  Hence  the  mem- 


STRUCTURE    OF    THE    LUNGS. 


157 


The  trachea,  or  tube  through  which  air  passes  to  the  lungs, 
divides  into  two  branches — one  for  each  lung ;  and  these  primary 
branches,  or  bronchi,  after  entering  the  substance  of  the  organ, 
divide  and  subdivide  into  a  number  of  smaller  and  smaller 
branches,  which  penetrate  to  every  part  of  the  organ,  until  at 
length  they  end  in  the  smaller  subdivisions  of  the  lung  called 
lobules.  All  the  larger  branches  have  walls  formed  of  tough 
membrane,  containing  portions  of  cartilaginous  rings,  by  which 

FIG.  57. 


A  diagrammatic  representation  of  the  heart  and  great  vessels  in  connection  with 
the  lungs — Y&.  The  pericardium  has  been  removed,  and  the  lungs  are  turned  aside- 
1,  right  auricle;  2,  vena  cava  superior,  3,  vena  cava  inferior ;  4,  right  ventricle ;  5, 
stem  of  the  pulmonary  artery ;  a  a,  its  right  and  left  branches ;  6,  left  auricular 
appendage;  7,  left  ventricle ;  8,  aorta;  9,  10,  the  two  lobes  of  the  left  lung;  11,  12) 
13,  the  three  lobes  of  the  right  lung  ;  b  b,  right  and  left  bronchi;  v  v,  right  and.  left 
upper  pulmonary  veins. 

they  are  held  open,  and  unstriped  muscular  fibres,  as  well  as 
longitudinal  bundles  of  elastic  tissue.  They  are  lined  by  mu- 
cous membrane,  the  surface  of  which,  like  that  of  the  larynx 
and  trachea,  is  covered  with  vibratile  ciliary  epithelium  (Fig. 
Ooj. 

As  the  bronchi  divide  they  become  smaller  and  smaller,  and 
their  walls  thinner ;  the  cartilaginous  rings  especially  becom- 

brane  which  covers  the  lung  is  called  the  visceral  layer  of  the  pleura, 
and  that  which  lines  the  walls  and  floor  of  the  chest  the  parietal  l&yer. 
The  appearance  of  a  cavity  or  space  (Fig.  56)  between  the  visceral 
layer  of  pleura  (covering  the  lungs)  and  the  parietal  layer  (covering 
the  inner  surface  of  the  wall  of  the  chest  and  upper  part  of  the  dia- 
phragm) is  only  inserted  for  the  sake  of  distinctness. 

14 


158  RESPIRATION. 

ing  scarcer  and  more  irregular,  until,  in  the  smaller  bronchial 
tubes,  they  are  represented  only  by  minute  and  scattered  car- 
tilaginous flakes.  And  when  the  bronchi,  by  successive 
branches,  are  reduced  to  about  ^  of  an  inch  in  diameter, 
they  lose  their  cartilaginous  element  altogether,  and  their 
walls  are  formed  only  of  a  tough,  fibrous,  elastic  membrane, 
with  traces  of  circular  muscular  fibres ;  they  are  still  lined, 
however,  by  a  thin  mucous  membrane,  with  ciliated  epithe- 
lium. 

Each  lung  is  partially  subdivided  into  separate  portions, 
called  lobes;  the  right  lung  into  three  lobes,  and  the  left  lung 
into  two  (Fig.  57).  Each  of  these  lobes,  again,  is  composed 

FIG.  58. 


Ciliary  epithelium  of  the  human  trachea  magnified  350  diameters,  a,  layer  of 
longitudinally  arranged  elastic  fibres  ;  b,  basement-memhrane  ;  c,  deepest  cells,  cir- 
cular in  form  ;  d,  intermediate  elongated  cells;  e,  outermost  layer  of  cells  fully  de- 
veloped and  bearing  cilia  (after  Kolliker). 

of  a  large  number  of  minute  parts,  called  lobules.  Each  pul- 
monary lobule  may  be  considered  a  lung  in  miniature,  consist- 
ing, as  it  does,  of  a  branch  of  the  bronchial  tube,  of  air-cells, 
bloodvessels,  nerves,  and  lymphatics,  with  a  sparing  amount 
of  areolar  tissue. 

On  entering  a  lobule,  the  small  bronchial  tube  divides  and 
subdivides ;  its  walls,  at  the  same  time,  becoming  thinner  and 
thinner,  until  at  length  they  are  formed  only  of  a  thin  mem- 
brane of  areolar  and  elastic  tissue,  lined  by  a  layer  of  squamous 
epithelium,  not  provided  with  cilia.  At  the  same  time,  they 
are  altered  in  shape ;  each  of  the  minute  terminal  branches 
widening  out  funnel-wise,  and  its  walls  being  pouched  out  ir- 
regularly into  small  saccular  dilatations,  called  air-cells  (Fig. 
59).  Such  a  funnel-shaped  terminal  branch  of  the  bronchial 
tube,  with  its  group  of  pouches  or  air-cells,  has  been  called  an 
infundibulwn  (Fig.  59),  and  the  irregular  oblong  space  in  its 


STRUCTURE    OF    THE    LUNGS. 


159 


FIG.  59. 


centre,  with  which  the  air-cells  communicate,  an  intercellular 
passage. 

The  air-cells  may  be  placed  singly,  like  recesses  from  the  in- 
tercellular passage,  but  more  often  they  are  arranged  in  groups 
or  even  in  rows,  like  minute  sac- 
culated  tubes  ;  so  that  a  short  se- 
ries of  cells,  all  communicating 
with  one  another,  open  by  a 
common  orifice  into  the  tube. 
The  cells  are  of  various  forms, 
according  to  the  mutual  pres- 
sure to  which  they  are  subject ; 
their  walls  are  nearly  in  con- 
tact, and  they  vary  from  jfG  to 
Jfi  of  an  inch  in  diameter. 
Their  walls  are  formed  of  fine 
membrane,  similar  to  that  of 
the  intercellular  passages,  and 
continuous  with  it,  which  mem- 
brane is  folded  on  itself  so  as  to 
form  a  sharp-edged  border  at 
each  circular  orifice  of  commu- 
nication between  contiguous  air- 
cells,  or  between  the  cells  and 
the  bronchial  passages.  Nu- 
merous fibres  of  elastic  tissue 
are  spread  out  between  con- 
tiguous air-cells,  and  many  of  these  are  attached  to  the  outer 
surface  of  the  fine  membrane  of  which  each  cell  is  composed, 
imparting  to  it  additional  strength,  and  the  power  of  recoil 
after  distension  (Fig.  60,  b  and  c).  The  cells  are  lined  by  a 
layer  of  squamous  or  tessellated  epithelium,  not  provided  with 
cilia.  Outside  the  cells,  a  network  of  pulmonary  capillaries 
is  spread  out  so  densely  (Fig.  61),  that  the  interspaces  or 
meshes  are  even  narrower  than  the  vessels,  which  are,  on  an 
average,  -g^1^  of  an  inch  in  diameter.  Between  the  atmo- 
spheric air  in  the  cells  and  the  blood  in  these  vessels,  nothing 
intervenes  but  the  thin  membranes  of  the  cells  and  capilla- 
ries and  the  delicate  epithelial  lining  of  the  former ;  and  the 
exposure  of  the  blood  to  the  air  is  the  more  complete,  because 
the  folds  of  membrane  between  contiguous  cells,  and  often  the 
spaces  between  the  walls  of  the  same,  contain  only  a  single 
layer  of  capillaries,  both  sides  of  which  are  thus  at  once  ex- 
posed to  the  air. 

The  cells  situated  nearest  to  the  centre  of  the  lung  are 


Two  small  groups  of  air-cells,  or 
infundihvla,  a  a,  with  air  cells,  b  6,  and 
the  ultimate  bronchial  tubes,  c  c,  with 
which  the  air-cells  communicate. 
From  a  new-born  child  (after  Kolliker). 


160 


RESPIRATION. 


smaller,  and   their  networks  of  capillaries   are  closer  than 
those  nearer  to  the  circumference,  in  adaptation  to  the  more 

FIG. 


Air-cells  of  lung,  magnified  350  diameters,  a,  epithelial  lining  of  the  cells;  6, 
fibres  of  elastic  tissue  ;  c,  delicate  membrane  of  which  the  cell-wall  is  constructed 
with  elastic  fibres  attached  to  it  (after  Kolliker). 

FIG.  61. 


Capillary  network  of  the  pulmonary  bloodvessels  in  the  human  lung  (from 
Kolliker)  \°. 


MECHANISM    OF    RESPIKATIOX.  161 

ready  supply  of  fresh  air  to  the  central  than  the  peripheral 
portion  of  the  lungs.  The  cells  of  adjacent  lobules  do  not 
communicate ;  and  those1  of  the  same  lobule,  or  proceeding 
from  the  same  intercellular  passage,  do  so  as  a  general  rule 
only  near  angles  of  bifurcation ;  so  that,  when  any  bronchial 
tube  is  closed  or  obstructed,  the  supply  of  air  is  lost  for  all 
the  cells  opening  into  it  or  its  branches. 

Mechanism  of  Respiration. 

For  the  proper  understanding  of  the  mechanism  by  which 
air  enters  and  is  expelled  from  the  lungs,  the  following  facts 
must  be  borne  in  mind : 

The  lungs  form  two  distinct  hollow  bags  (communicating 
with  the  exterior  through  the  trachea  and  larynx),  and  are 
always  closely  in  contact  with  the  inner  surface  of  the  chest- 
walls,  while  their  lower  portions  are  closely  in  contact  with 
the  diaphragm,  or  muscular  partition  which  separates  the 
chest  from  the  abdomen  (Figs.  31  and  65).  The  lungs  follow 
all  movements  of  the  parts  in  contact  with  them  ;  and  for  the 
evident  reason  that  the  outer  surface  of  the  lung-bag  not  being 
exposed  directly  to  atmospheric  pressure,  while  the  inner  sur- 
face is  so  exposed,  the  pressure  from  within  preserves  the  lungs 
in  close  contact  with  the  parts  surrounding  them,  and  obliter- 
ates, practically,  the  pleural  space,  and  must  continue  to  do 
so,  until  from  some  cause  or  other — say  from  an  opening  for 
the  admission  of  air  through  the  chest-walls,  the  pressure  on 
the  outside  of  the  lung  equals  or  exceeds  that  on  the  interior. 
Any  such  artificial  condition  of  things,  however,  need  not  here 
be  considered. 

For  the  inspiration  of  air  into  the  lungs  it  will  be  evident 
from  the  foregoing  facts  that  all  that  is  necessary  is  such  a 
movement  of  the  side-walls  or  floor  of  the  chest,  or  of  both, 
that  the  capacity  of  the  interior  shall  be  enlarged.  By  such 
increase  of  capacity  there  will  be  of  course  a  diminution  of  the 
pressure  of  the  air  in  the  lungs,  and  a  fresh  quantity  will  enter 
through  the  larynx  and  trachea  to  equalize  the  pressure  on 
the  inside  and  outside  of  the  chest.  For  the  expiration  of  air, 
on  the  other  hand,  it  is  also  evident  that,  by  an  opposite  move- 
ment which  shall  contract  the  capacity  of  the  chest,  the  pres- 
sure in  the  interior  will  be  increased,  and  air  will  be  expelled, 
until  the  pressures  within  and  without  the  chest  are  again 
equal.  In  both  cases  the  air  passes  through  the  trachea  and 
larynx,  whether  in  entering  or  leaving  the  lungs,  there  being 
no  other  communication  with  the  exterior,  and  the  lung,  for 
the  reason  before  mentioned,  remains  under  all  the  circum- 


162  RESPIRATION. 

stances  described,  closely  in  contact  with  the  walls  and  floor 
of  the  chest.  To  speak  of  expansion  of  the  chest  is  to  speak 
also  of  expansion  of  the  lung. 

We  have  now  to  consider  the  means  by  which  the  chest- 
cavity  is  alternately  enlarged  and  contracted  for  the  entrance 
and  expulsion  of  atmospheric  air ;  or,  in  technical  terms,  for 
inspiration  and  expiration. 

Respiratory  Movements. 

The  chest  is  a  cavity  filled  by  the  lungs,  heart,  and  large 
bloodvessels,  &c.,  and  closed  everywhere  against  the  entrance  of 
air  except  by  the  way  of  the  larynx  and  trachea.  It  is  bounded 
behind  and  at  the  sides  by  the  spine  and  ribs,  and  in  front  by 
the  sternum  and  cartilages  of  the  ribs.  Its  floor  is  formed 
mainly  by  the  diaphragm. 

The  immediate  inner  lining  of  all  these  parts  is  the  outer 
or  polished  layer  of  the  pleura ;  and  this  membrane  also  is 
stretched  continuously  across  the  top  of  the  chest-cavity,  and 
mainly  forms  its  roof. 

The  enlargement  of  the  capacity  of  the  chest  in  inspiration 
is  a  muscular  act ;  the  muscles  concerned  in  producing  the 
effect  being  chiefly  the  diaphragm  and  the  external  intercostal 
muscles,  with  that  part  of  the  internal  intercostal  which  is  be- 
tween the  cartilages  of  the  ribs.  These  are  assisted  by  the 
levatores  costarum,  the  serratus  posticus  superior,  and  some 
others. 

The  vertical  diameter  of  the  chest  is  increased  by  the  con- 
traction and  consequent  descent  of  the  diaphragm — the  sides 
of  the  muscle  descending  most,  and  the  central  tendon  remain- 
ing comparatively  unmoved,  while  the  intercostal  and  other 
muscles  just  mentioned,  by  acting  at  the  same  time,  not  only 
prevent  the  diaphragm  during  its  contraction  from  drawing  in 
the  sides  of  the  chest,  but  increase  the  diameter  of  the  chest  in 
the  lateral  direction,  by  elevating  the  ribs ;  that  is  to  say,  by 
rotating  them,  to  speak  roughly,  around  an  axis  passing 
through  their  sternal  and  spinal  attachments — somewhat  after 
the  fashion  of  raising  the  handle  of  a  bucket  (Fig.  62).  This 
is  not  all,  however.  Another  effect  of  the  contraction  of  the 
intercostal  muscles  is  to  increase  the  antero-posterior  diameter 
of  the  chest — by  partially  straightening  out  the  angle  between 
the  rib  and  its  cartilage,  and  thus  lengthening  the  distance 
between  its  spinal  and  sternal  attachments  (Fig.  62,  A).  In 
this  way,  at  the  same  time  that  the  ribs  are  raised,  the  sternum 
is  pushed  forward.  This  forward  movement  of  the  sternum, 
which  is  accompanied  by  a  slight  upward  movement,  is  in  part 


RESPIRATORY     MOVEMENTS.  163 

accomplished  also  by  a  raising  of  the  anterior  extremities  of 
the  rib  cartilages,  which  of  course,  in  any  movement,  carry 
the  sternum  with  them.  The  differences  in  shape  and  direc- 

FIG.  G2. 


tion  of  the  upper  and  lower  true  ribs,  and  the  more  acute 
angles  formed  by  the  junction  of  the  latter  with  their  carti- 
lages, make  the  effect  much  greater  at  the  lower  than  at  the 
upper  part  of  the  chest. 

The  expansion  of  the  chest  in  inspiration  presents  some  pe- 
culiarities in  different  persons  and  circumstances.  In  young 
children,  it  is  effected  almost  entirely  by  the  diaphragm,  which 
being  highly  arched  in  expiration,  becomes  flatter  as  it  con- 
tracts, and,  descending,  presses  on  the  abdominal  viscera,  and 
pushes  forward  the  front  walls  of  the  abdomen.  The  move- 
ment of  the  abdominal  walls  being  here  more  manifest  than 
that  of  any  other  part,  it  is  usual  to  call  this  the  abdominal 
mode  or  type  of  respiration.  In  adult  men,  together  with  the 
descent  of  the  diaphragm,  and  the  pushing  forward  of  the 
front  wall  of  the  abdomen,  the  lower  part  of  the  chest  and 
the  sternum  are  subject  to  a  wide  movement  in  inspiration. 
In  women,  the  movement  appears  less  extensive  in  the  lower, 
and  more  so  in  the  upper,  part  of  the  chest ;  a  mode  of  breath- 
ing to  which  a  greater  mobility  of  the  first  rib  is  adapted,  and 
which  may  have  for  its  object  the  provision  of  sufficient  space 
for  respiration  when  the  lower  part  of  the  chest  is  encroached 
upon  by  the  pregnant  uterus.  MM.  Beau  and  Maissiat  call 
the  former  the  inferior  costal,  and  the  latter  the  superior  costal, 
type  of  respiration ;  but  the  annexed  diagrams  will  explain 
the  difference  better  than  the  names  will,  for  these  imply  a 


164 


RESPIRATION. 


greater  diversity  than  naturally  exists   in  the  modes  of  in- 
spiration. 

From  the  enlargement  produced  in  inspiration,  the  chest 
and  lungs  return  in  ordinary  tranquil  expiration,  by  their  elas- 
ticity ;  the  force  employed  by  the  inspiratory  muscles  in  dis- 


FlG.  64. 


FIG.  63  (after  Hutchinson).— The  changes  of  the  thoracic  and  abdominal  walls  of 
the  male  during  respiration.  The  back  is  supposed  to  be  fixed  in  order  to  throw  for- 
ward the  respiratory  movement  as  much  as  possible.  The  outer  black  continuous 
line  in  front  represents  the, ordinary  breathing  movement ;  the  anterior  margin  of 
it  being  the  boundary  of  inspiration,  the  posterior  margin  the  limit  of  expiration. 
The  line  is  thicker  over  the  abdomen^-eince  the  ordinary  respiratory  movement  is 
chiefly  abdominal :  thin  over  the  chest,  for  there  is  less  movement  over  that  region. 
The  dotted  line  indicates  the  movement  on  deep  inspiration,  during  which  the  ster- 
num advances  while  the  abdomen  recedes. 

FIG.  64  (after  Hutchinson).— The  respiratory  movement  in  the  female.  The  lines 
indicate  the  same  changes  as  in  the  last  figure.  The  thickness  of  the  continuous  line 
over  the  sternum  shows  the  larger  extent  of  the  ordinary  breathing  movement  over 
that  region  in  the  female  than  in  the  male. 

tending  the  chest  and  overcoming  the  elastic  resistance  of  the 
lungs  and  chest-walls,  being  returned  as  an  expiratory  effort 
when  the  muscles  are  relaxed.  This  elastic  recoil  of  the  rib- 
cartilages,  but  also  of  the  lungs  themselves,  in  consequence  of 
the  elastic  tissue  which  they  contain  in  considerable  quantity, 
is  sufficient,  in  ordinary  quiet  breathing,  to  expel  air  from  the 
chest  in  the  intervals  of  inspiration,  and  no  muscular  power 


RESPIRATORY     RHYTHM.  165 

is  required.  In  all  voluntary  expiratory  efforts,  however,  as 
in  speaking,  singing,  blowing,  and  the  like,  and  in  many  in- 
voluntary actions  also,  as  sneezing,  coughing,  &c.,  something 
more  than  merely  passive  elastic  power  is  of  course  necessary, 
and  the  proper  expiratory  muscles  are  brought  into  action. 
By  far  the  chief  of  these  are  the  abdominal  muscles,  which, 
by  pressing  on  the  viscera  of  the  abdomen,  push  up  the  floor 
of  the  chest  formed  by  the  diaphragm,  and  by  thus  making 
pressure  on  the  lungs,  expel  air  from  them  through  the  trachea 
and  larynx.  All  muscles,  however,  which  depress  the  ribs, 
must  act  also  as  muscles  of  expiration,  and  therefore  we  must 
conclude  that  the  abdominal  muscles  are  assisted  in  their  ac- 
tion by  the  greater  part  of  the  internal  intercostals,  the  trian- 
gularis  sterui,  the  serratus  posticus  inferior,  &c.  When  by 
the  efforts  of  the  expiratory  muscles,  the  chest  has  been 
squeezed  to  less  than  its  average  diameter,  it  again,  on  relaxa- 
tion of  the  muscles,  returns  to  the  normal  dimensions  by  virtue 
of  its  elasticity.  The  construction  of  the  chest- walls,  there- 
fore, admirably  adapts  them  for  recoiling  against  and  resisting 
as  well  undue  contraction  as  undue  dilatation. 

As  before  mentioned,  the  lungs,  after  distension  in  the  act 
of  inspiration,  contract  by  virtue  of  the  elastic  tissue  which  is 
present  in  the  bronchial  tubes,  on  and  between  the  air-cells, 
and  in  the  investing  pleura.  But  in  the  natural  condition  of 
the  parts,  they  can  never  contract  to  the  utmost,  but  are  always 
more  or  less  "  on  the  stretch,"  being  kept  closely  in  contact 
with  the  inner  surface  of  the  walls  of  the  chest  by  atmospheric 
pressure  able  to  act  only  on  their  interior,  and  can  contract 
away  from  these  only  when,  by  some  means  or  other,  as  by 
making  an  opening  into  the  pleural  cavity,  or  by  the  effusion 
of  fluid  there,  the  pressure  on  the  exterior  and  interior  of  the 
lungs  becomes  equal.  Thus,  under  ordinary  circumstances, 
the  degree  of  contraction  or  dilatation  of  the  lungs  is  dependent 
on  that  of  the  boundary  walls  of  the  chest,  the  outer  surface  of 
the  one  being  in  close  contact  with  the  inner  surface  of  the 
other,  and  obliged  to  follow  it  in  all  its  movements. 

Respiratory  Rhythm. 

The  acts  of  expansion  and  contraction  of  the  chest,  take  up 
under  ordinary  circumstances  a'  nearly  equal  time,  and  can 
scarcely  be  said  to  be  separated  from  each  other  by  an  inter- 
vening pause. 

The  act  of  inspiring  air,  however,  especially  in  women  and 
children,  is  a  little  shorter  than  that  of  expelling  it,  and  there 
is  commonly  a  very  slight  pause  between  the  end  of  expiration 


166  RESPIRATION. 

and  the  beginning  of  the  next  inspiration.     The  respiratory 
rhythm  may  be  thus  expressed: 

Inspiration, ........     6 

Expiration, 7  or  8 

A  very  slight  pause. 

Respiratory  Movements  of  the  Glottis. 

During  the  action  of  the  muscles  which  directly  draw  air 
into  the  chest,  those  which  guard  the  opening  through  which 
it  enters  are  not  passive.  In  hurried  breathing  the  instinctive 
dilatation  of  the  nostrils  is  well  seen,  although  under  ordinary 
conditions  it  may  not  be  noticeable.  The  opening  at  the  upper 
part  of  the  larynx,  however,  or  rima  glottidis  (Fig.  65),  is  di- 
lated at  each  inspiration,  for  the  more  ready  passage  of  air, 
and  collapses  somewhat  at  each  expiration,  its  condition,  there- 
fore, corresponding  during  respiration  with  that  of  the  walls  of 
the  chest.  There  is  a  further  likeness  between  the  two  acts 
in  that,  under  ordinary  circumstances,  the  dilatation  of  the 
rima  glottidis  is  a  muscular  act,  and  its  contraction  chiefly  an 
elastic  recoil ;  although,  under  various  conditions,  to  be  here- 
after mentioned,  there  may  be,  in  the  contraction  of  the  glottis, 
considerable  muscular  power  exercised. 

Quantity  of  Air  Respired. 

The  quantity  of  air  that  is  changed  in  the  lungs  in  each  act 
of  ordinary  tranquil  breathing  is  variable,  and  is  very  difficult 
to  estimate,  because  it  is  hardly  possible  to  breathe  naturally 
while,  as  in  an  experiment,  one  is  attending  to  the  process. 
Probably  30  to  35  cubic  inches  are  a  fair  average  in  the  case 
of  healthy  young  and  middle-aged  men ;  but  Bourgery  is  per- 
haps right  in  saying,  that  old  people,  even  in  health,  habitu- 
ally breathe  more  deeply,  and  change  in  each  respiration  a 
larger  quantity  of  air  than  younger  persons  do. 

The  total  quantity  of  air  which  passes  into  and  out  of  the 
lungs  of  an  adult,  at  rest,  in  24  hours,  has  been  estimated  by 
Dr.  E.  Smith  at  about  686,000  cubic  inches.  This  quantity, 
however,  is  largely  increased  by  exertion ;  and  the  same  ob- 
server has  computed  the  average  amount  for  a  hard-working 
laborer  in  the  same  time,  at  1,568,390  cubic  inches. 

The  quantity  which  is  habitually  and  almost  uniformly 
changed  in  each  act  of  breathing,  is  called  by  Mr.  Hutchinson 
breathing  air.  The  quantity  over  and  above  this  which  a  man 
can  draw  into  the  lungs  in  the  deepest  inspiration,  he  names 
complemental  air :  its  amount  is  various,  as  will  be  presently 


QUANTITY    OF     AIR     RESPIRED.  167 

shown.  After  ordinary  expiration,  such  as  that  which  expels 
the  breathing  air,  a  certain  quantity  of  air  remains  in  the  lungs, 
which  may  be  expelled  by  a  forcible  and  deeper  expiration : 
this  he  terms  reserve  air.  But,  even  after  the  most  violent  ex- 
piratory effort,  the  lungs  are  not  completely  emptied ;  a  certain 
quantity  always  remains  in  them,  over  which  there  is  no  vol- 
untary control,  and  which  may  be  called  residual  air.  Its 
amount  depends  in  great  measure  on  the  absolute  size  of  the 
chest,  and  has  been  variously  estimated  at  from  forty  to  two 
hundred  and  sixty  cubic  inches. 

The  greatest  respiratory  capacity  of  the  chest  is  indicated 
by  the  quantity  of  air  which  a  person  can  expel  from  his  lungs 
by  a  forcible  expiration  after  the  deepest  inspiration  that  he 
can  make.  Mr.  Hutchinson  names  this  the  vital  capacity :  it 
expresses  the  power  which  a  person  has  of  breathing  in  the 
emergencies  of  active  exercise,  violence,  and  disease;  and  in 
healthy  men  it  varies  according  to  stature,  weight,  and  age. 

It  is  found  by  Mr.  Hutchinson,  from  whom  most  of  our  in- 
formation on  this  subject  is  derived,  that  at  a  temperature  of 
60°  F.,  225  cubic  inches  is  the  average  vital  capacity  of  a 
healthy  person,  five  feet  seven  inches  in  height.  For  every 
inch  of  height  above  this  standard  the  capacity  is  increased, 
on  an  average,  by  eight  cubic  inches ;  and  for  every  inch  be- 
low, it  is  diminished  by  the  same  amount.  This  relation  of 
capacity  to  height  is  quite  independent  of  the  absolute  capacity 
of  the  cavity  of  the  chest;  for  the  cubic  contents  of  the  chest 
do  not  always,  or  even  generally,  increase  with  the  stature  of 
the  body ;  and  a  person  of  small  absolute  capacity  of  chest  may 
have  a  large  capacity  of  respiration,  and  vice  versa.  The  ca- 
pacity of  respiration  is  determined  only  by  the  mobility  of  the 
walls  of  the  chest;  but  why  this  mobility  should  increase  in  a 
definite  ratio  with  the  height  of  the  body  is  yet  unexplained, 
and  must  be  difficult  of  solution,  seeing  that  the  height  of  the 
body  is  chiefly  determined  by  that  of  the  legs,  and  not  by  the 
height  of  the  trunk  or  the  depth  of  the  chest.  But  the  vast 
number  of  observations  made  by  Mr.  Hutchinson  seem  to  leave 
no  doubt  of  the  fact  as  stated  above. 

The  influence  of  weight  on  the  capacity  of  respiration  is  less 
manifest  and  considerable  than  that  of  height:  and  it  is  diffi- 
cult to  arrive  at  any  definite  conclusions  on  this  point,  because 
the  natural  average  weight  of  a  healthy  man  in  relation  to 
stature  has  not  yet  been  determined.  As  a  general  statement, 
however,  it  may  be  said  that  the  capacity  of  respiration  is  not 
affected  by  weights  under  161  pounds,  or  11 1  stones;  but  that, 
above  this  point,  it  is  diminished  at  the  rate  of  one  cubic  inch 
for  every  additional  pound  up  to  196  pounds,  or  14  stones;  so 


168  RESPIRATION. 

that,  for  example,  while  a  man  of  five  feet  six  inches,  and 
weighing  less  than  Hi  stones,  should  be  able  to  expire  217 
cubic  inches,  one  of  the  same  height,  weighing  12 £  stones, 
might  expire  only  203  cubic  inches. 

By  age,  the  capacity  appears  to  be  increased  from  about  the 
fifteenth  to  the  thirty-fifth  year,  at  the  rate  of  five  cubic  inches 
per  year;  from  thirty -five  to  sixty-five  it  diminishes  at  the 
rate  of  about  one  and  a  half  cubic  inch  per  year ;  so  that  the 
capacity  of  respiration  of  a  man  of  sixty  years  old  would  be 
about  30  cubic  inches  less  than  that  of  a  man  forty  years  old, 
of  the  same  height  and  weight. 

Mr.  Hutchinson's  observations  were  made  almost  exclusively 
on  men ;  and  his  conclusions  are,  perhaps,  true  of  them  alone ; 
for  women,  according  to  Bourgery,  have  only  half  the  capacity 
of  breathing  that  men  of  the  same  age  have. 

The  number  of  respirations  in  a  healthy  adult  person  usually 
ranges  from  fourteen  to  eighteen  per  minute. 

It  is  greater  in  infancy  and  childhood ;  and  of  course  varies 
much  according  to  different  circumstances,  such  as  exercise  or 
rest,  health  or  disease,  &c.  Variations  in  the  number  of  res- 
pirations correspond  ordinarily  with  similar  variations  in  the 
pulsations  of  the  heart.  In  health  the  proportion  is  about 
one  to  four,  or  one  to  five,  and  when  the  rapidity  of  the  heart's 
action  is  increased,  that  of  the  chest  movement  is  commonly 
increased  also  ;  but  not  in  every  case  in  equal  proportion.  It 
happens  occasionally  in  disease,  especially  of  the  lungs  or  air- 
passages,  that  the  number  of  respiratory  acts  increases  in 
quicker  proportion  than  the  beats  of  the  pulse  ;  and,  in  other 
affections,  much  more  commonly,  that  the  number  of  the  pulses 
is  greater  in  proportion  than  that  of  the  respirations. 

According  to  Mr.  Hutchinson,  the  force  with  which  the  in- 
spiratory  muscles  are  capable  of  acting,  is  greatest  in  individ- 
uals of  the  height  of  from  five  feet  seven  inches  to  five  feet 
eight  inches,  and  will  elevate  a  column  of  three  inches  of 
mercury.  Above  this  height,  the  force  decreases  as  the  stat- 
ure increases ;  so  that  the  average  of  men  of  six  feet  can 
elevate  only  about  two  and  a  half  inches  of  mercury.  The 
force  manifested  in  the  strongest  expiratory  acts  is,  on  the 
average,  one-third  greater  than  that  exercised  in  inspiration. 
But  this  difference  is  in  great  measure  due  to  the  power  ex- 
erted by  the  elastic  reaction  of  the  walls  of  the  chest ;  and  it 
is  also  much  influenced  by  the  disproportionate  strength  which 
the  expiratory  muscles  attain,  from  their  being  called  into  use 
for  other  purposes  than  that  of  simple  expiration.  The  force 
of  the  inspiratory  act  is,  therefore,  better  adapted  than  that  of 
the  expiratory,  for  testing  the  muscular  strength  of  the  body. 


QUANTITY    OF     AIR     RESPIRED. 


169 


The  following  table  expresses  the  result  of  numerous  exper- 
iments by  Mr.  Hutchinson  on  this  subject,  the  instrument  used 
to  gauge  the  inspiratory  and  expiratory  power  being  a  hsema- 
dynamometer  (see  p.  138),  to  which  was  attached  a  tube  fitting 
the  nostrils,  and  through  which  the  inspiratory  or  expiratory 
eifort  was  made : 


Power 
Inspiratory 

1.5  i 
2.0 
2.5 
3.5 
4.5 
5.5 
6.0 
7.0 

of 
Muscles. 

n.     .     . 

Ex 

Weak 

Power 
piratory 

2  Oil 
2.5  < 
3.5  ' 
4.5  • 
5.8  ' 
7.0  ' 
8.5  < 
10.0  ' 

of 

Muscles. 

l. 

Ordinary,     .... 

Strong,    .          ... 
Very  strong,     .     .     . 
Remarkable,     .     .     . 
Very  remarkable, 
Extraordinary,      .     . 
Very  extraordinary,  . 

Mr.  Hutchinson  remarks :  "  Suppose  a  man  to  lift  by  his 
inspiratory  muscles  three  inches  of  mercury,  what  muscular 
effort  has  he  used  ?  The  mere  quantity  of  fluid  lifted  may  be 
very  inconsiderable  (and  as  such  1  have  found  men  wonder 
they  could  not  elevate  more),  but  not  so  the  power  exerted, 
when  we  recollect  that  hydrostatic  law,  which  Mr.  Bramah 
adopted  to  the  construction  of  a  very  convenient  press.  To 
apply  this  law  here,  the  diaphragm  alone  must  act  under  such 
an  effort,  with  a  force  equal  to  the  weight  of  a  column  of  mer- 
cury 3  inches  in  height,  and  whose  base  is  commensurate  to 
the  area  of  the  diaphragm.  The  area  of  the  base  of  one  of 
the  chests  now  before  the  Society,  is  57  square  inches ;  there- 
fore, had  this  man  raised  3  inches  of  mercury  by  his  inspira- 
tory muscles,  his  diaphragm  alone  in  this  act  must  have  op- 
posed a  resistance  equal  to  more  than  23  ounces  on  every  inch 
of  that  muscle,  and  a  total  weight  of  more  than  83  pounds. 
Moreover,  the  sides  of  his  chest  would  resist  a  pressure  from 
the  atmosphere  equal  to  the  weight  of  a  covering  of  mercury 
three  inches  in  thickness,  or  more  than  23  ounces  on  every 
inch  surface,  which,  if  we  take  at  318  square  inches,  the  chest 
will  be  found  resisting  a  pressure  of  731  pounds;  and  allowing 
the  elastic  resistance  of  the  ribs  as  1^  inch  of  mercury,  this 
will  bring  the  weight  resisted  by  the  chest,  as  follows : 


Diaphragm, 
Walls  of  the  chest, 
Elastic  force,     . 


83  Ibs. 
731    " 
232    " 


Total, 1046 

"In  round  numbers  it  may  be  said,  that  the  parietes  of  the 


170  RESPIRATION. 

thorax  resisted  1000  Ibs.  of  atmospheric  pressure,  and  that  not 
counterbalanced, — to  say  nothing  of  the  elastic  power  of  the 
lungs,  which  co-operated  with  this  pressure. 

"  I  would  not  venture  at  present  to  state  exactly  the  distri- 
bution of  muscular  fibre  over  the  thorax,  which  is  called  into 
action  when  resisting  this  1046  Ibs.,  but  I  think  I  am  safe  in 
stating  that  nine-tenths  of  the  thoracic  surface  conspire  to 
this  act. 

"  What  is  here  said  of  the  muscular  part  of  the  chest  resist- 
ing such  a  force,  must  not  be  confounded  with  a  former  state- 
ment of  'two-thirds  being  lifted  by  the  inspiratory  muscles,  and 
one-third  left  dormant,'  under  a  force  equal  to  301  Ibs.  In 
this  case  the  301  Ibs.  are  lifted;  in  the  other,  nine-tenths  of 
1046  Ibs.  are  said  to  be  resisted. 

"  The  glass  receiver  of  an  air-pump  may  resist  15  Ibs.  on  the 
square  inch,  yet  it  may  be  said  to  lift  nothing.  This  question 
of  the  thoracic  muscular  force  and  resistance,  and  muscular 
distribution,  is  rendered  complicate  by  the  presence  of  so  much 
osseous  matter  entering  into  the  composition  of  the  chest,  which 
can  scarcely  be  considered  to  act  the  same  as  muscle." 

The  great  force  of  the  iuspiratory  efforts  during  apnoea  was 
well  shown  in  some  of  the  experiments  performed  by  the  Medico- 
chirurgical  Society's  Committee  on  Suspended  Animation.  On 
inserting  a  glass  tube  into  the  trachea  of  a  dog,  and  immersing 
the  other  end  of  the  tube  in  a  vessel  of  mercury,  the  respiratory 
efforts  during  apnoea  were  so  great  as  to  draw  the  mercury  four 
inches  up  the  tube.  The  influence  of  the  same  force  was  shown 
in  other  experiments,  in  which  the  heads  of  animals  were  im- 
mersed both  in  mercury  and  in  liquid  plaster  of  paris.  In  both 
cases  the  material  was  found,  after  death,  to  have  been  drawn 
up  into  all  the  bronchial  tubes,  filling  the  tissue  of  the  lungs. 

Much  of  the  force  exerted  in  inspiration  is  employed  in  over- 
coming the  resistance  offered  by  the  elasticity  of  the  walls  of 
the  chest  and  of  the  lungs.  Mr.  Hutchinson  estimated  the 
amount  of  this  elastic  resistance,  by  observing  the  elevation  of 
a  column  of  mercury  raised  by  the  return  of  air  forced,  after 
death,  into  the  lungs,  in  quantity  equal  to  the  known  capacity 
of  respiration  during  life ;  and  he  calculated  that,  in  a  man 
capable  of  breathing  200  cubic  inches  of  air,  the  muscular 
power  expended  upon  the  elasticity  of  the  walls  of  the  chest, 
in  making  the  deepest  inspiration,  would  be  equal  to  the  rais- 
ing of  at  least  301  pounds  avoirdupois.  To  this  mus-t  be  added 
about  150  Ibs.  for  the  elastic  resistance  of  the  lungs  themselves, 
so  that  the  total  force  to  be  overcome  by  the  muscles  in  the 
act  of  inspiring  200  cubic  inches  of  air  is  more  than  450  Ibs. 

In  tranquil  respiration,  supposing  the  amount  of  breathing 


VITAL    CAPACITY.  171 

air  to  be  twenty  cubic  inches,  the  resistance  of  the  walls  of  the 
chest  would  be  equal  to  lifting  more  than  100  pounds ;  and  to 
this  must  be  added  about  70  pounds  for  the  elasticity  of  the 
lungs.  The  elastic  force  overcome  in  ordinary  inspiration 
must,  therefore,  be  equal  to  about  170  pounds. 

It  is  probable,  that  in  the  quiet  ordinary  respiration,  which 
is  performed  without  consciousness  or  effort  of  the  will,  the 
only  forces  engaged  are  those  of  the  inspiratory  muscles,  and 
the  elasticity  of  the  walls  of  the  chest  and  the  lungs.  It  is 
not  known  under  what  circumstances  the  contractile  power 
which  the  bronchial  tubes  possess,  by  means  of  their  organic 
muscular  fibres,  is  brought  into  action.  It  is  possible,  as  Dr. 
R.  Hall  maintained,  that  it  may  exist  in  expiration ;  but  it  is 
more  likely  that  its  chief  purpose  is  to  regulate  and  adapt,  in 
some  measure,  the  quantity  of  air  admitted  to  the  lungs,  and 
to  each  part  of  them,  according  to  the  supply  of  blood. 
Another  purpose  probably  served  by  the  muscular  fibres  of  the 
bronchial  tubes  is  that  of  contracting  upon  and  gradually  ex- 
pelling collections  of  mucus,  which  may  have  accumulated 
within  the  tubes,  and  cannot  be  ejected  by  forced  expiratory 
efforts,  owing  to  collapse  or  other  morbid  conditions  of  the  por- 
tion of  lung  proceeding  from  the  obstructed  tubes  (Gairdner). 

The  muscular  action  in  the  lungs,  morbidly  excited,  is  prob- 
ably the  chief  cause  of  the  phenomena  of  spasmodic  asthma. 
It  may  be  demonstrated  by  galvanizing  the  lungs  shortly  after 
taking  them  from  the  body.  Under  such  a  stimulus,  they 
contract  so  as  to  lift  up  water  placed  in  a  tube  introduced  into 
the  trachea  (C.  J.  B.  Williams) ;  and  Volkmann  has  shown 
that  they  may  be  made  to  contract  by  stimulating  their 
nerves.  He  tied  a  glass  tube,  drawn  fine  at  one  end,  into  the 
trachea  of  a  beheaded  animal ;  and  when  the  small  end  was 
turned  to  the  flame  of  a  candle,  he  galvanized  the  pneumo- 
gastric  trunk.  Each  time  he  did  so  the  flame  was  blown,  and 
once  it  was  blown  out. 

The  changes  of  the  air  in  the  lungs  effected  by  these  respi- 
ratory movements  are  assisted  by  the  various  conditions  of  the 
air  itself.  According  to  the  law  observed  in  the  diffusion  of 
gases,  the  carbonic  acid  evolved  in  the  air-cells  will,  inde- 
pendently of  any  respiratory  movement,  tend  to  leave  the 
lungs,  by  diffusing  itself  into  the  external  air,  where  it  exists 
in  less  proportion  ;  and  according  to  the  same  law,  the  oxygen 
of  the  atmospheric  air  will  tend  of  itself  towards  the  air-cells 
in  which  its  proportion  is  less  than  it  is  in  the  air  in  the  bron- 
chial tubes  or  iu  that  external  to  the  body.  But  for  this  ten- 
dency in  the  oxygen  and  carbonic  acid  to  mix  uniformly, 
within  and  without  the  lungs,  the  reserve  and  residual  air 


172  RESPIRATION. 

would,  probably,  be  very  injuriously  charged  with  carbonic 
acid ;  for  the  respiratory  movements  alone  are  not  enough  to 
empty  the  air-cells,  and  perhaps  expel  only  the  air  which  lies 
in  the  larger  bronchial  tubes.  Probably  also  the  change  is 
assisted  by  the  different  temperature  of  the  air  within  and 
without  the  lungs  ;  and  by  the  action  of  the  cilia  on  the  mu- 
cous membrane  of  the  bronchial  tubes,  the  continual  vibra- 
tions of  which  may  serve  to  prevent  the  adhesion  of  the  air  to 
the  moist  surface  of  the  membrane. 

Movement  of  Blood  in  the  Respiratory  Organs. 

To  be  exposed  to  the  air  thus  alternately  moved  into  and 
out  of  the  air-cells  and  minute  bronchial  tubes,  the  blood  is 
propelled  from  the  right  ventricle  through  the  pulmonary  cap- 
illaries in  steady  streams,  and  slowly  enough  to  permit  every 
minute  portion  of  it  to  be  for  a  few  seconds  exposed  to  the  air, 
with  only  the  thin  walls  of  the  capillary  vessels  and  air-cells 
intervening.  The  pulmonary  circulation  is  of  the  simplest 
kind  :  for  the  pulmonary  artery  branches  regularly ;  its  suc- 
cessive branches  run  in  straight  lines,  and  do  not  anastomose ; 
the  capillary  plexus  is  uniformly  spread  over  the  air-cells  and 
intercellular  passages ;  and  the  veins  derived  from  it  proceed 
in  a  course  as  simple  and  uniform  as  that  of  the  arteries,  their 
branches  converging  but  not  anastomosing.  The  veins  have 
no  valves,  or  only  small  imperfect  ones  prolonged  from  their 
angles  of  junction,  and  incapable  of  closing  the  orifice  of  either 
of  the  veins  between  which  they  are  placed.  The  pulmonary 
circulation  also  is  unaffected  by  changes  of  atmospheric  pres- 
sure, and  is  not  exposed  to  the  influence  of  the  pressure  of 
muscles :  the  force  by  which  it  is  accomplished,  and  the  course 
of  the  blood  are  alike  simple. 

The  blood  which  is  conveyed  to  the  lungs  by  the  pulmonary 
arteries  is  distributed  to  these  organs  to  be  purified  and  made 
fit  for  the  nutrition  of  all  other  parts  of  the  body.  The  capil- 
laries of  the  pulmonary  vessels  are  arranged  solely  with  refer- 
ence to  this  object,  and  therefore  can  have  but  little  to  do  with 
the  nutrition  of  the  lungs ;  or,  at  least,  only  of  those  portions 
of  the  lungs  with  which  they  are  in  intimate  connection  for 
another  purpose.  For  the  nutrition  of  the  rest  of  the  lungs, 
including  the  pleura,  interlobular  tissue,  bronchial  tubes  and 
glands,  and  the  walls  of  the  larger  bloodvessels,  a  special 
supply  of  arterial  blood  is  furnished  through  one  or  two  bron- 
chial arteries,  the  branches  of  which  ramify  in  all  these  parts. 
The  blood  of  the  bronchial  artery,  when,  having  served  for 
the  nutrition  of  these  parts,  it  has  become  venous,  is  carried 


CHANGES    OF     AIR    IN     RESPIRATION.        173 

partly  into  the  branches  of  the  bronchial  vein,  and  thence  to 
the  right  auricle,  and  partly  into  the  small  branches  of  the 
pulmonary  artery,  or,  more  directly,  into  the  pulmonary  capil- 
laries, whence,  being  with  the  rest  of  the  blood  arterialized,  it 
is  carried  to  the  pulmonary  veins  and  left  side  of  the  heart. 

Changes  of  the  Air  in  Respiration. 

By  their  contact  in  the  lungs  the  composition  of  both  air 
and  blood  is  changed.  The  alterations  of  the  former  being 
manifest,  simpler  than  those  of  the  latter,  and  in  some  degree 
illustrative  of  them,  may  be  considered  first. 

The  atmosphere  we  breathe  has,  in  every  situation  in  which 
it  has  been  examined  in  its  natural  state,  a  nearly  uniform 
composition.  It  is  a  mixture  of  oxygen,  nitrogen,  carbonic 
acid,  and  watery  vapor,  with,  commonly,  traces  of  other  gases, 
as  ammonia,  sulphuretted  hydrogen,  &c.  Of  every  100  vol- 
umes of  pure  atmospheric  air,  79  volumes  (on  an  average) 
consist  of  nitrogen,  the  remaining  21  of  oxygen.  The  propor- 
tion of  carbonic  acid  is  extremely  small ;  10,000  volumes  of 
atmosperic  air  contain  only  about  4  or  5  of  carbonic  acid. 

The  quantity  of  watery  vapor  varies  greatly,  according  to 
the  temperature  and  other  circumstances,  but  the  atmosphere 
is  never  without  some.  In  this  country,  the  average  quantity 
of  watery  vapor  in  the  atmosphere  is  1.40  per  cent. 

The  changes  produced  by  respiration  on  the  atmospheric  air 
are,  that,  1,  it  is  warmed ;  2,  its  carbonic  acid  is  increased ; 
3,  its  oxygen  is  diminished ;  4,  its  watery  vapory  is  increased ; 
5,  a  minute  amount  of  organic  matter  and  of  free  ammonia  is 
added  to  it. 

1.  The  expired  air,  heated  by  its  contact  with  the  interior 
of  the  lungs,  is  (at  least  in  most  climates)  hotter  than  the  in- 
spired air.     Its  temperature  varies  between  97°  and  99^°,  the 
lower  temperature  being  observed  'when  the  air  has  remained 
but  a  short  time  in  the  lungs,  rather  than  when  it  is  inhaled 
at  a  very  low  temperature ;  for  whatever  the  temperature  when 
inhaled  may  be,  the  air  nearly  acquires  that  of  the  blood  be- 
fore it  is  expelled  from  the  chest. 

2.  The  carbonic  acid  in  respired  air  is  always  increased;  but 
the  quantity  exhaled  in  a  given  time  is  subject  to  change  from 
various  circumstances.  'From  every  volume  of  air  inspired, 
about  4?  per  cent,  of  oxygen  are  abstracted  ;  while  a  rather 
smaller  quantity  of  carbonic  acid  is  added  in  its  place.     It 
may  be  stated,  as  a  general  average  deduced  from  the  results 
of  experiments  by  Valentin  and  Brunner,  that,  under  ordi- 
nary circumstances,  the    quantity  of   carbonic  acid  exhaled 

15 


174  RESPIRATION. 

into  the  air  breathed  by  a  healthy  adult  man  amounts  to 
1346  cubic  inches,  or  about  636  grains  per  hour.  According 
to  this  estimate,  which  corresponds  very  closely  with  the  one 
furnished  by  Sir  H.  Davy,  and  does  not  widely  differ  from 
those  obtained  by  Allen  and  Pepys,  Lavoisier,  and  Dr.  Ed. 
Smith,  the  weight  of  carbon  excreted  from  the  lungs  is  about 
173  grains  per  hour,  or  rather  more  than  8  ounces  in  the  course 
of  twenty-four  hours.  Discrepancies  in  the  results  obtained 
by  different  experimenters  may  be  due  to  the  variations  to 
which  the  exhalation  of  carbonic  acid  is  liable  in  different 
circumstances  ;  for  even  in  health  the  quantity  varies  accord- 
ing to  age,  sex,  diversities  in  the  respiratory  movements,  ex- 
ternal temperature,  the  degree  of  purity  of  the  respired  air, 
and  other  circumstances.  Each  of  these  deserves  a  brief  notice, 
because  it  affords  evidence  concerning  either  the  sources  of 
carbonic  acid  exhaled,  or  the  mode  in  which  it  is  separated 
from  the  blood. 

a.  Influence   of  Age   and  Sex. — According   to  Andral  and 
Gavarret  the  quantity  of  carbonic  acid  exhaled  into  the  air 
breathed  by  males,  regularly  increases  from  eight  to  thirty 
years  of  age ;  from  thirty  to  forty  it  is  stationary  or  diminishes 
a  little;  from  forty  to  fifty  the  diminution  is  greater ;  and  from 
fifty  to  extreme  age  it  goes  on  diminishing,  till  it  scarcely 
exceeds  the  quantity  exhaled  at  ten  years  old.     In  females 
(in  whom  the  quantity  exhaled  is  always  less  than  in  males 
of  the  same  age)  the  same  regular  increase  in  quantity  goes 
on  from  the  eighth  year  to  the  age  of  puberty,  when  the  quan- 
tity  abruptly  ceases  to  increase,  and  remains   stationary  so 
long  as  they  continue  to  menstruate.     When,  however,  men- 
struation has   ceased,  either  in  advancing  years  or  in  preg- 
nancy or  morbid  amenorrhoea,  the  exhalation  of  carbonic  acid 
again  augments ;  but  when  menstruation  ceases  naturally,  it 
soon  decreases  again  at  the  same  rate  that  it  does  in  old  men. 

b.  Influence  of  Respiratory  Movements. — According  to  Vier- 
ordt,  the  more  quickly  the  movements  of  respiration  are  per- 
formed, the  smaller  is  the  proportionate  quantity  of  carbonic 
acid  contained  in  each  volume  of  the  expired  air.     Thus  he 
found  that,  with  six  respirations  per  minute,  the  quantity  of 
expired  carbonic  acid  was  5.528  per  cent. ;  with  twelve  respi- 
rations, 4.262  per  cent. ;  with  twenty-four,  3.355 ;  with  forty- 
eight,  2.984  ;  and  with  ninety-six,  2.662.     Although,  however, 
the  proportionate  quantity  of  carbonic  acid  is  thus  diminished 
during  frequent  respiration,  yet  the  absolute  amount  exhaled 
into  the  air  within  a  given  time  is  increased  thereby,  owing 
to  the  larger  quantity  of  air  which  is  breathed  in  the  time. 
This  is  the  case,  whether  the  respiration  be  voluntarily  accel- 


TEMPERATURE    AND    SEASON.  175 

erated,  or  naturally  increased  in  frequency,  as  it  is  after  feed- 
ing, active  exercise,  &c.  By  diminishing  the  frequency,  and 
increasing  the  depth  of  respiration,  the  percentage  proportion 
of  carbonic  acid  in  the  expired  air  is  diminished ;  being  in  the 
deepest  respiration  as  much  as  1.97  per  cent,  less  than  in  ordi- 
nary breathing.  But  for  this  proportionate  diminution  also, 
there  is  a  full  compensation  in  the  greater  total  volume  of 
air  which  is  thus  breathed.  Finally,  the  last  half  of  a  volume 
of  expired  air  contains  more  carbonic  acid  than  the  half  first 
expired ;  a  circumstance  which  is  explained  by  the  one  por- 
tion of  air  coming  from  the  remote  part  of  the  lungs,  where  it 
has  been  in  more  immediate  and  prolonged  contact  with  the 
blood  than  the  other  has,  which  comes  chiefly  from  the  larger 
bronchial  tubes. 

c.  Influence  of   External   Temperature.  —  The   observations 
made  by  Vierordt  at  various  temperatures  between  38°  F.  and 
75°  F.  show,  for  warm-blooded  animals,  that  within  this  range, 
every  rise  equal  to  10°  F.  causes  a  diminution  of  about  two 
cubic  inches  in  the  quantity  of  carbonic  acid  exhaled   per 
minute.     Letellier,  from  experiments  performed  on  animals 
at  much  higher  and  lower  temperatures  than  the  above,  also 
found  that  the  higher  the  temperature  of  the  respired  air  (as 
far  as  104°  F.),  the  less  is  the  amount  of  carbonic  acid  exhaled 
into  it,  whilst  the  nearer  it  approaches  zero  the  more  does  the 
carbonic  acid  increase.     The  greatest  quantity  exhaled  at  the 
lower  temperatures  he  found  to  be  about  twice  as  much  as  the 
smallest  exhaled  at  the  higher  temperatures. 

d.  Season  of  the  Year. — Dr.  Edward  Smith  has  shown  that 
the  season  of  the  year,  independently  of  temperature,  also  ma- 
terially influences  the  respiratory  phenomena ;  for  with  the 
same  temperature,  at  different  seasons,  there  is  a  great  diversity 
in  the  amount  of  carbonic  acid  expired.     According  to  his 
observations,  spring  is  the  season  of  the  greatest,  and  autumn 
of  the  least  activity  of  the  respiratory  and  other  functions. 

e.  Purity  of  the  Respired  Air. — The  average  quantity  of  car- 
bonic acid  given  out  by  the  lungs  constitutes  about  4.48  per 
cent,  of  the  expired  air ;  but  if  the  air  which  is  breathed  be 
previously  impregnated  with  carbonic  acid  (as  is  the  case  when 
the  same  air  is  frequently  respired),  then  the  quantity  of  car- 
bonic acid  exhaled  becomes  much  less.     This  is  shown  by  the 
results  of  two  experiments  performed  by  Allen  and  Pepys.    In 
one,  in  which  fresh  air  was  taken  in  at  each  respiration,  thirty- 
two  cubic  inches  of  carbonic  acid  were  exhaled  in  a  minute; 
whilst  in  the  other,  in  which  the  same  air  was  respired  repeat- 
edly, the  quantity  of  carbonic  acid  emitted  in  the  same  time 
was  only  9.5  cubic  inches.     They  found  also  that,  however 


176  RES  PI  BAT  I  ON. 

often  the  same  air  may  be  respired,  even  if  until  it  will  no  longer 
sustain  life,  it  does  not  become  charged  with  more  than  ten 
per  cent,  of  carbonic  acid.  The  necessity  of  a  constant  supply 
of  fresh  air,  by  means  of  ventilation,  through  rooms  in  which 
many  persons  are  breathing  together,  or  in  which,  from  any 
other  source,  much  carbonic  acid  is  evolved,  is  thus  rendered 
obvious ;  for  even  when  the  air  is  not  completely  irrespirable, 
yet  in  the  same  proportion  as  it  is  already  charged  with  car- 
bonic acid,  does  the  further  extrication  of  that  gas  from  the 
lungs  suffer  hindrance. 

/.  Hygrometric  State  of  Atmosphere. — Lehmann's  observations 
have  shown  that  the  amount  of  carbonic  acid  exhaled  is  con- 
siderably influenced  by  the  degree  of  moisture  of  the  atmo- 
sphere, much  more  being  given  off  when  the  air  is  moist  than 
when  it  is  dry. 

g.  Period  of  the  Day. — The  period  of  day  seems  to  exercise  a 
slight  influence  on  the  amount  of  carbonic  acid  exhaled  in  a 
given  time,  though  beyond  the  fact  that  the  quantity  exhaled 
is  much  less  by  night,  we  are  scarcely  yet  in  a  position  to  state 
that  variations  in  the  amount  exhaled  occur  at  uniform  periods 
of  the  day,  independently  of  the  influence  of  other  circum- 
stances. 

h.  Food. — By  the  use  of  food  the  quantity  is  increased,  whilst 
by  fasting  it  is  diminished :  and,  according  to  Regnault  and 
Reiset,  it  is  greater  when  animals  are  fed  on  farinaceous  food 
than  when  fed  on  meat.  Spirituous  drinks,  especially  when 
taken  on  an  empty  stomach,  are  generally  believed  to  pro- 
duce an  immediate  and  marked  diminution  in  the  quantity 
of  this  gas  exhaled.  Recent  observations  by  Dr.  Edward 
Smith,  however,  furnish  some  singular  results  on  this  subject. 
Dr.  Smith  found,  for  example,  that  the  effects  produced  by 
spirituous  drinks  depend  much  on  the  kind  of  drink  taken. 
Pure  alcohol  tended  rather  to  increase  than  to  lessen  respira- 
tory changes,  and  the  amount,  therefore,  of  carbonic  acid  ex- 
pired :  rum,  ale,  and  porter,  also  sherry,  had  very  similar  effects. 
On  the  other  hand,  brandy,  whisky,  and  gin,  particularly  the 
latter,  almost  always  lessened  the  respiratory  changes,  and 
consequently  the  amount  of  carbonic  acid  exhaled. 

i.  Exercise  and  Sleep. — Bodily  exercise,  in  moderation,  in- 
creases the  quantity  to  about  one-third  more  than  it  is  during 
rest ;  and  for  about  an  hour  after  exercise,  the  volume  of  the 
air  expired  in  the  minute  is  increased  about  118  cubic  inches ; 
and  the  quantity  of  carbonic  acid  about  7.8  cubic  inches  per 
minute.  Violent  exercise,  such  as  full  labor  on  the  tread- 
wheel,  still  further  increases,  according  to  Dr.  E.  Smith,  the 
amount  of  the  acid  exhaled. 


EFFECTS    OF     EXERCISE     AND    SLEEP.        177 

During  sleep,  on  the  other  hand,  there  is  a  considerable 
diminution  in  the  quantity  of  this  gas  evolved  ;  a  result, 
probably,  in  great  measure  dependent  on  the  tranquillity  of 
breathing ;  directly  after  walking,  there  is  a  great,  though 
quickly  transitory,  increase  in  the  amount  exhaled.  A  larger 
quantity  is  exhaled  when  the  barometer  is  low  than  when  it 
is  high. 

3.  The  Oxygen  in  Respired  Air  is  always  less  than  in  the 
same  air  before  respiration,  and  its  diminution  is  generally 
proportionate  to  the  increase  of  the  carbonic  acid.  The  ex- 
periments of  Valentin  and  Brunner  seem  to  show  that  for 
every  volume  of  carbonic  acid  exhaled  into  the  air,  1.17421 
volumes  of  oxygen  are  absorbed  from  it ;  and  that  when  the 
average  quantity  of  carbonic  acid,  i.  e.,  1346  cubic  inches,  or 
636  grains,  is  exhaled  in  the  hour,  the  quantity  of  oxygen  ab- 
sorbed in  the  same  time  is  1584  cubic  inches,  or  542  grains. 
According  to  this  estimate,  there  is  more  oxygen  absorbed 
than  is  exhaled  with  carbon  to  form  carbonic  acid  without 
change  of  volume ;  and  to  this  general  conclusion,  namely, 
that  the  volume  of  air  expired  in  a  given  time  is  less  than 
that  of  the  air  inspired  (allowance  being  made  for  the  expan- 
sion in  being  heated),  and  that  the  loss  is  due  to  a  portion  of 
oxygen  absorbed  and  not  returned  in  the  exhaled  carbonic 
acid,  all  observers  agree,  though  as  to  the  actual  quantity  of 
oxygen  so  absorbed,  they  differ  even  widely. 

The  quantity  of  oxygen  that  does  not  combine  with  the 
carbon  given  off  in  carbonic  acid  from  the  lungs,  is  probably 
disposed  of  in  forming  some  of  the  carbonic  acid  and  water 
given  off  from  the  skin,  and  in  combining  with  sulphur  and 
phosphorus  to  form  part  of  the  acids  of  the  sulphates  and 
phosphates  excreted  in  the  urine,  and  probably  also,  from  the 
experiments  of  Dr.  Bence  Jones,  with  the  nitrogen  of  the  de- 
composing nitrogenous  tissues. 

The  quantity  of  oxygen  consumed  seems  to  vary  much,  not 
only  in  different  individuals,  but  in  the  same  individual  at 
different  periods ;  thus  it  is  considerably  influenced  by  food, 
being  greater  in  dogs  when  fed  on  farinaceous  than  on  animal 
food,  and  much  diminished  during  fasting,  while  it  varies  at 
different  stages  of  digestion.  Animals  of  small  size  consume 
a  relatively  much  greater  amoujit  of  oxygen  than  larger  ones. 
The  quantity  of  oxygen  in  the  atmosphere  surrounding  animals 
appears  to  have  very  little  influence  on  the  amount  of  this  gas 
absorbed  by  them,  for  the  quantity  consumed  is  not  greater 
even  though  an  excess  of  oxygen  be  added  to  the  atmosphere 
experimented  with  (Regnault  and  Reiset). 

The  Nitrogen  of  the  Atmosphere,  in  relation  to  the  respira- 


178  RESPIRATION. 

tory  process,  is  supposed  to  serve  only  mechanically,  by  dilut- 
ing the  oxygen,  and  moderating  its  action  upon  the  system. 
This  purpose,  or  the  mode  of  expressing  it,  has  been  denied 
by  Liebig,  on  the  ground  that  if  we  suppose  the  nitrogen  re- 
moved, the  amount  of  oxygen  in  a  given  space  would  not  be 
altered.  But,  although  it  be  true  that  if  all  the  nitrogen  of 
the  atmosphere  were  removed  and  not  replaced  by  any  other 
gas,  the  oxygen  might  still  extend  over  the  whole  space  at 
present  occupied  by  the  mixture  of  which  the  atmosphere  is 
composed ;  yet  since,  under  ordinary  circumstances,  oxygen 
and  nitrogen,  when  mixed  together  in  the  ratio  of  one  volume 
to  four,  produce  a  mixture  which  occupies  precisely  five  vol- 
umes, with  all  the  properties  of  atmospheric  air,  it  must  result 
that  a  given  volume  of  atmosphere  drawn  into  the  lungs  con- 
tains four-fifths  less  weight  of  oxygen  than  an  equal  volume 
composed  entirely  of  oxygen.  The  greater  rapidity  and  bril- 
liancy with  which  combustion  goes  on  in  an  atmosphere  of 
oxygen  than  in  one  of  common  air,  and  the  increased  rapidity 
with  which  the  ordinary  effects  of  respiration  are  produced 
when  oxygen  instead  of  atmospheric  air  is  breathed,  seem  to 
leave  no  doubt  that  the  nitrogen  with  which  the  oxygen  of  the 
atmosphere  is  mixed  has  the  effect  of  diluting  this  gas,  in  the 
same  sense  and  degree  as  one  part  of  alcohol  is  diluted  when 
mixed  with  four  parts  of  water. 

It  has  been  often  discussed  whether  nitrogen  is  ever  ab- 
sorbed by  or  exhaled  from  the  lungs  during  respiration. 

At  present,  all  that  can  be  said  on  the  subject  is  that,  under 
most  circumstances,  animals  appear  to  expire  a  very  small 
quantity  above  that  which  exists  in  the  inspired  air.  During 
prolonged  fasting,  on  the  contrary,  a  small  quantity  appears  to 
be  absorbed. 

4.  Watery  Vapor  is,  under  ordinary  circumstances,  always 
exhaled  from  the  lungs  in  breathing.  The  quantity  emitted  is, 
as  a  general  rule,  sufficient  to  saturate  the  expired  air,  or  very 
nearly  so.  Its  absolute  amount  is,  therefore,  influenced  by  the 
following  circumstances.  First,  by  the  quantity  of  air  respired  ; 
for  the  greater  this  is,  the  greater  also  will  be  the  quantity  of 
moisture  exhaled.  Secondly,  by  the  quantity  of  watery  vapor 
contained  in  the  air  previous  to  its  being  inspired ;  because  the 
greater  this  is,  the  less  will  be  the  amount  required  to  complete 
the  saturation  of  the  air.  Thirdly,  by  the  temperature  of  the  ex- 
pired air;  for  the  higher  this  is,  the  greater  will  be  the  quantity 
of  watery  vapor  required  to  saturate  the  air.  Fourthly,  by 
the  length  of  time  which  each  volume  of  inspired  air  is  allowed 
to  remain  in  the  lungs ;  for  it  seems  probable  that,  although 
during  ordinary  respiration  the  expired  air  is  always  saturated 


CHANGES    IN    BLOOD.  179 

with  watery  vapor,  yet  when  respiration  is  performed  very 
rapidly  the  air  has  scarcely  time  to  be  raised  to  the  highest 
temperature,  or  be  fully  charged  with  moisture  ere  it  is  expelled. 

For  ordinary  cases,  however,  it  may  be  held  that  the  ex- 
pired air  is  saturated  with  watery  vapor,  and  hence  is  derivable 
a  means  of  estimating  the  quantity  exhaled  in  any  given  time : 
namely,  by  subtracting  the  quantity  contained  in  the  air  in- 
spired from  the  quantity  which  (at  the  barometric  pressure) 
would  saturate  the  same  air  at  the  temperature  of  expiration, 
which  is  ordinarily  about  99°.  And,  on  the  other  hand,  if  the 
quantity  of  watery  vapor  in  the  expired  air  be  estimated,  the 
quantity  of  air  itself  may  from  it  be  determined,  being  as  much 
as  that  quantity  of  watery  vapor  would  saturate  at  the  ascer- 
tained temperature  and  barometric  pressure. 

The  quantity  of  water  exhaled  from  the  lungs  in  twenty- 
four  hours  ranges  (according  to  the  various  modifying  circum- 
stances already  mentioned)  from  about  6  to  27  ounces,  the  or- 
dinary quantity  being  about  9  or  10  ounces.  Some  of  this  is 
probably  formed  by  the  combination  of  the  excess  of  oxygen 
absorbed  in  the  lungs  with  the  hydrogen  of  the  blood  ;  but  the 
far  larger  proportion  of  it  must  be  the  mere  exhalation  of  the 
water  of  the  blood,  taking  place  from  the  surfaces  of  the  air- 
passages  and  cells,  as  it  does  from  the  free  surfaces  of  all  moist 
animal  membranes,  particularly  at  the  high  temperature  of 
warm-blooded  animals.  It  is  exhaled  from  the  lungs  what- 
ever be  the  gas  respired,  continuing  to  be  expelled  even  in 
hydrogen  gas. 

5.  The  Rev.  J.  B.  Reade  showed,  some  years  ago,  and  Dr. 
Richardson's  experiments  confirm  the  fact,  that  ammonia  is 
among  the  ordinary  constituents  of  expired  air.  It  seems 
probable,  however,  both  from  the  fact  that  this  substance  can- 
not be  always  detected,  and  from  its  minute  amount  when 
present,  that  the  whole  of  it  may  be  derived  from  decomposing 
particles  of  food  left  in  the  mouth,  or  from  carious  teeth  or  the 
like  ;  and  that  it  is,  therefore,  only  an  accidental  constituent  of 
expired  air. 

The  quantity  of  organic  matter  in  the  breath  has  been  lately 
investigated  by  Dr.  Ransome,  who  calculates  that  about  3 
grains  are  given  off  from  the  lungs  of  an  adult  in  twenty-four 
hours. 

Changes  produced  in  the  Blood  by  Respiration. 

The  most  obvious  change  which  the  blood  undergoes  in  its 
passage  through  the  lungs  is  that  of  color,  the  dark  crimson  of 
venous  blood  being  exchanged  for  the  bright  scarlet  of  arterial 
blood.  (The  circumstances  which  have  been  supposed  to  give 


180  RESPIKATIOX. 

rise  to  this  change,  the  conditions  capable  of  effecting  it  inde- 
pendent of  respiration,  and  some  other  differences  between 
arterial  and  venous  blood,  were  discussed  in  the  chapter  on 
Blood,  p.  77):  2d,  and  in  connection  with  the  preceding 
change,  it  gains  oxygen;  3d,  it  loses  carbonic  acid;  4th,  it  be- 
comes 1°  or  2°  F.  warmer;  5th,  it  coagulates  sooner  and  more 
firmly,  and,  apparently,  contains  more  fibrin. 

The  oxygen  absorbed  into  the  blood  from  the  atmospheric 
air  in  the  lungs  is  combined  chemically  with  the  haemoglobin 
of  the  red  blood-corpuscles.  In  this  condition  it  is  carried  in 
the  arterial  blood  to  the  various  parts  of  the  body,  and  with  it 
is,  in  the  capillary  system  of  vessels,  brought  into  near  relation 
or  contact  with  the  elementary  parts  of  the  tissues.  Herein, 
co-operating  probably  in  the  process  of  nutrition,  or  in  the  re- 
moval of  disintegrated  parts  of  the  tissues,  a  certain  portion  of 
the  oxygen  which  the  arterial  blood  contains  disappears,  and 
a  proportionate  quantity  of  carbonic  acid  and  water  is  formed. 

But  it  is  not  alone  in  the  disintegrating  processes  to  which 
all  parts  of  the  body  are  liable,  that  oxygen  is  consumed  and 
carbonic  acid  and  water  are  formed  in  its  consumption.  A 
like  process  occurs  in  the  blood  itself,  independently  of  the 
decay  of  the  tissues;  for  on  the  continuance  of  such  chemical 
processes  depend,  directly  or  indirectly,  not  only  the  tempera- 
ture of  the  body,  but  all  the  forces,  the  nervous,  the  muscular, 
and  others,  manifested  by  the  living  organism. 

The  venous  blood,  containing  the  new-formed  carbonic  acid, 
returns  to  the  lungs,  where  a  portion  of  the  carbonic  acid  is 
exhaled,  and  a  fresh  supply  of  oxygen  is  again  taken  in. 

Mechanism  of  Various  Respiratory  Actions. 

It  will  be  well  here,  perhaps,  to  explain  some  respiratory 
acts,  which  appear  at  first  sight  somewhat  complicated,  but 
cease  to  be  so  when  the  mechanism  by  which  they  are  per- 
formed is  clearly  understood.  The  accompanying  diagram 
(Fig.  65)  shows  that  the  cavity  of  the  chest  is  separated  from 
that  of  the  abdomen  by  the  diaphragm,  which,  when  acting, 
will  lessen  its  curve,  and  thus  descending,  will  push  downwards 
and  forwards  the  abdominal  viscera;  while  the  abdominal 
muscles  have  the  opposite  effect,  and  in  acting  will  push  the 
viscera  upwards  and  backward,  and  with  them  the  diaphragm, 
supposing  its  ascent  to  be  not  from  any  cause  interfered  with. 
From  the  same  diagram  it  will  be  seen  that  the  lungs  commu- 
nicate with  the  exterior  of  the  body  through  the  glottis,  and 
further  on  through  the  mouth  and  nostrils — through  either  of 
them  separately,  or  through  both  at  the  same  time,  according 


MECHANISM    OF    RESPIRATORY    ACTIONS.       181 

to  the  position  of  the  soft  palate.  The  stomach  communicates 
with  the  exterior  of  the  body  through  the  ossophagus,  pharynx, 
and  mouth;  while  below7,  the  rectum  opens  at  the  anus,  and 
the  bladder  through  the  urethra.  All  these  openings,  through 
which  the  hollow  viscera  communicate  with  the  exterior  of  the 
body,  are  guarded  by  muscles,  called  sphincters,  which  can 

FJO.   65. 


act  independently  of  each  other.     The  position  of  the  latter  is 
indicated  in  the  diagram. 

Let  us  take  first  the  simple  act  of  sighing.  In  this  case 
there  is  a  rather  prolonged  inspiratory  effort  by  the  diaphragm 
and  other  muscles  concerned  in  inspiration  ;  the  air  almost 
noiselessly  passing  in  through  the  glottis,  and  by  the  elastic 
recoil  of  the  lungs  and  chest-walls,  and  probably  also  of  the 
abdominal  walls,  being  rather  suddenly  expelled  again. 

16 


182  RESPIRATION. 

Now,  in  the  first,  or  inspiratory  part  of  this  act,  the  descent 
of  the  diaphragm  presses  the  abdominal  viscera  downwards, 
and  of  course  this  pressure  tends  to  evacuate  the  contents  of 
such  as  communicate  with  the  exterior  of  the  body.  Inasmuch, 
however,  as  their  various  openings  are  guarded  by  sphincter 
muscles,  in  a  state  of  constant  tonic  contraction,  there  is  no 
escape  of  their  contents,  and  air  simply  enters  the  lungs.  In 
the  second,  or  expiratory  part  of  the  act  of  sighing,  there  is  also 
pressure  made  on  the  abdominal  viscera  in  the  opposite  direc- 
tion, by  the  elastic  or  muscular  recoil  of  the  abdominal  walls  ; 
but  the  pressure  is  relieved  by  the  escape  of  air  through  the 
open  glottis,  and  the  relaxed  diaphragm  is  pushed  up  again 
into  its  original  position.  The  sphincters  of  the  stomach,  rec- 
tum, and  bladder  act  as  before. 

Hiccough  resembles  sighing  in  that  it  is  an  inspiratory  act, 
but  the  inspiration  is  sudden  instead  of  gradual,  from  the 
diaphragm  acting  suddenly  and  spasmodically ;  and  the  air, 
therefore,  suddenly  rushing  through  the  unprepared  rima 
glottidis,  causes  vibration  of  the  vocal  cords,  and  the  peculiar 
sound. 

In  the  act  of  coughing,  there  is  most  often  first  an  inspira- 
tion, and  this  is  followed  by  an  expiration  ;  but  when  the  lungs 
have  been  filled  by  the  preliminary  inspiration,  instead  of  the 
air  being  easily  let  out  again  through  the  glottis,  the  latter  is 
momentarily  closed  by  the  approximation  of  the  vocal  cords ; 
and  then  the  abdominal  muscles,  strongly  acting,  push  up  the 
viscera  against  the  diaphragm,  and  thus  make  pressure  on  the 
air  in  the  lungs  until  its  tension  is  sufficient  to  burst  open 
noisily  the  vocal  cords  which  oppose  its  outward  passage.  In 
this  way  a  considerable  force  is  exercised,  and  mucus  or  any 
other  matter  that  may  need  expulsion  from  the  lungs  or  trachea 
is  quickly  and  sharply  expelled  by  the  out-streaming  current 
of  air. 

Now  it  is  evident  on  reference  to  the  diagram  (Fig.  65), 
that  pressure  exercised  by  the  abdominal  muscles  in  the  act  of 
coughing,  acts  as  forcibly  on  the  abdominal  viscera  as  on  the 
lungs,  inasmuch  as  the  viscera  form  the  medium  by  which  the 
upward  pressure  on  the  diaphragm  is  made,  and  of  necessity 
there  is  quite  as  great  a  tendency  to  the  expulsion  of  their  con- 
tents as  of  the  air  in  the  lungs.  The  instinctive  and,  if  neces- 
sary, voluntarily  increased  contraction  of  the  sphincters,  how- 
ever, prevents  any  escape  at  the  openings  guarded  by  them, 
and  the  pressure  is  effective  at  one  part  only,  namely,  the  rima 
glottidis. 

The  same  remarks  that  apply  to  coughing,  are  almost  ex- 
actly applicable  to  the  act  of  sneezing ;  but  in  this  instance 


VOMITING  —  PARTURITION.  183 

the  blast  of  air,  on  escaping  from  the  lungs,  is  directed  by  an 
instinctive  contraction  of  the  pillars  of  the  fauces  and  descent 
of  the  soft  palate,  chiefly  through  the  nose,  and  any  offending 
matter  is  thence  expelled. 

In  the  act  of  vomiting,  as  in  coughing,  there  is  first  an  in- 
spiration ;  the  glottis  is  then  closed,  and  immediately  after- 
wards the  abdominal  muscles  strongly  act ;  but  here  occurs 
the  difference  in  the  two  actions.  Instead  of  the  vocal  cords 
yielding  to  the  action  of  the  abdominal  muscles,  they  remain 
tightly  closed.  Thus  the  diaphragm  being  unable  to  go  up, 
forms  an  unyielding  surface  against  which  the  stomach  can  be 
pressed.  It  is  fixed,  to  use  a  technical  phrase.  At  the  same 
time  the  cardiac  sphincter  being  relaxed  while  the  pylorus  is 
closed  (see  Fig.  65),  and  the  stomach  itself  also  contracting, 
the  action  of  the  abdominal  muscles,  by  these  means  assisted, 
expels  the  contents  of  the  organ  through  the  oesophagus,  phar- 
ynx, and  mouth.  The  reversed  peristaltic  action  of  the 
oesophagus  probably  increases  the  effect. 

In  the  act  of  voluntary  expulsion  of  urine  or  faeces,  there 
is  first  an  inspiration,  as  in  coughing,  sneezing,  and  vomiting; 
the  glottis  is  then  closed,  and  the  diaphragm  fixed  as  in  vom- 
iting. Now,  however,  both  the  rima  glottidis  and  the  cardiac 
opening  of  the  stomach  remain  closed,  and  the  sphincter  of 
the  bladder  or  rectum,  or  of  both,  being  relaxed,  the  evacu- 
ation of  the  contents  of  these  viscera  takes  place  accordingly ; 
the  effect  being,  of  course,  increased  by  the  muscular  and 
elastic  contraction  of  their  own  walls.  As  before,  there  is  as 
much  tendency  to  the  escape  of  the  contents  of  the  lungs  or 
stomach  as  of  the  rectum  or  bladder ;  but  the  pressure  is  re- 
lieved only  at  the  orifice,  the  sphincter  of  which  instinctively 
or  involuntarily  yields. 

In  all  these  expulsive  actions  the  diaphragm  is  quite  pas- 
sive ;  and  when  it  is  fixed,  it  is  in  consequence  of  the  closure 
of  the  glottis  (which  by  preventing  the  exit  of  air  from  the 
lungs  prevents  its  upward  movement),  not  from  any  exertion 
on  its  own  part. 

In  females,  during  parturition,  almost  an  exactly  similar 
action  occurs,  so  far  as  the  diaphragm  and  abdominal  walls 
are  concerned,  to  that  which  takes  place  in  a  straining  effort 
at  expulsion  of  urine  or  faeces.  The  contraction  of  the  uterus, 
however,  is  both  relatively  and  absolutely  more  powerful  than 
that  of  the  bladder  or  rectum,  although  it  is  greatly  assisted 
by  the  inspiratory  effort,  by  the  fixing  of  the  diaphragm,  and 
by  the  action  of  the  abdominal  muscles,  as  in  the  other  acts 
just  described.  In  parturition,  as  in  vomiting,  the  action  of 
the  abdominal  muscles  is,  to  a  great  extent,  involuntary — more 


184  RESPIRATION. 

so  than  it  commonly  is  in  the  expulsion  of  faeces  or  urine;  but 
in  these  latter  instances  also,  in  cases  of  great  pain  and  diffi- 
culty, it  may  cease  to  be  a  voluntary  act,  and  be  quite  beyond 
the  control  of  the  will. 

In  speaking,  there  is  a  voluntary  expulsion  of  air  through 
the  glottis  by  means  of  the  abdominal  muscles ;  and  the  vocal 
cords  are  put,  by  the  muscles  of  the  larynx,  in  a  proper  posi- 
tion and  state  of  tension  for  vibrating  as  the  air  passes  over 
them,  and  thus  producing  sound.  The  sound  is  moulded  into 
words  by  the  tongue,  teeth,  lips,  &c. — the  vocal  cords  produc- 
ing the  sound  only,  and  having  nothing  to  do  with  articulation. 

Singing  resembles  speaking  in  the  manner  of  its  production ; 
the  laryngeal  muscles,  by  variously  altering  the  position  and 
degree  of  tension  of  the  vocal  cords,  producing  the  different 
notes.  Words  used  in  the  act  of  singing  are  of  course  framed, 
as  in  speaking,  by  the  tongue,  teeth,  lips,  &c. 

Sniffing  is  produced  by  a  somewhat  quick  action  of  the  dia- 
phragm and  other  inspiratory  muscles.  The  mouth  is,  how- 
ever, closed,  and  by  these  means  the  whole  stream  of  air  is 
made  to  enter  by  the  nostrils.  The  alse  nasi  are,  commonly, 
at  the  same  time,  instinctively  dilated. 

Sucking  is  not  properly  a  respiratory  act,  but  it  may  be 
most  conveniently  considered  in  this  place.  It  is  caused 
chiefly  by  the  depressor  muscles  of  the  os  hyoides.  These,  by 
drawing  downwards  and  backwards  the  tongue  and  floor  of 
the  mouth,  produce  a  partial  vacuum  in  the  latter ;  and  the 
weight  of  the  atmo&phere  then  acting  on  all  sides  tends  to  pro- 
duce equilibrium  on  the  inside  and  outside  of  the  mouth  as 
best  it  may.  The  communication  between  the  mouth  and 
pharynx  is  completely  shut  off,  probably  by  the  contraction  of 
the  pillars  of  the  soft  palate  and  descent  of  the  latter  so  as  to 
touch  the  back  of  the  tongue  ;  and  the  equilibrium,  therefore, 
can  be  restored  only  by  the  entrance  of  something  through  the 
mouth.  The  action,  indeed,  of  the  tongue  and  floor  of  the 
mouth  in  sucking  may  be  compared  to  that  of  the  piston  in  a 
syringe,  and  the  muscles  which  pull  down  the  os  hyoides  and 
tongue,  to  the  power  which  draws  the  handle. 

In  the  preceding  account  of  respiratory  actions,  the  dia- 
phragm and  abdominal  muscles  have  been,  as  the  chief  muscles 
engaged,  and  for  the  sake  of  clearness,  almost  alone  referred 
to.  But,  of  course,  in  all  inspiratory  actions,  the  other  muscles 
of  inspiration  (p.  162)  are  also  more  or  less  engaged ;  and  in 
expiration,  the  abdominal  muscles  are  assisted  by  others,  pre- 
viously enumerated  (p.  165)  as  grouped  in  action  with  them. 


INFLUENCE     OF    NERVOUS    SYSTEM.  185 

Influence  of  the  Nervous  System  in  Respiration. 

Like  all  other  functions  of  the  body,  the  discharge  of  which 
is  necessary  to  life,  respiration  must  be  essentially  an  involun- 
tary act.  Else,  life  would  be  in  constant  danger,  and  would 
cease  on  the  loss  of  consciousness  for  a  few  moments,  even  in 
sleep.  But  it  is  also  necessary  that  respiration  should  be  to 
some  extent  under  the  control  of  the  will.  For  were  it  not 
so,  it  would  be  impossible  to  perform  those  voluntary  respira- 
tory acts  which  have  been  just  enumerated  and  explained,  as 
speaking,  singing,  straining,  and  the  like. 

The  respiratory  movements  and  their  regular  rhythm,  so  far 
as  they  are  involuntary  and  independent  of  consciousness  (as 
on  all  ordinary  occasions  they  are),  seem  to  be  under  the  ab- 
solute governance  of  the  medulla  oblongata,  which,  as  a  ner- 
vous centre,  receives  the  impression  of  the  "  necessity  of 
breathing,"  and  reflects  it  to  the  phrenic  and  such  other  motor 
nerves  as  will  bring  into  co-ordinate  and  adapted  action  the 
muscles  necessary  to  inspiration. 

In  the  cases  of  voluntary  respiratory  acts,  we  may  believe 
that  the  brain,  as  well  as  the  medulla  oblongata,  is  engaged  in 
the  process ;  for  we  have  no  evidence  of  the  mind  exercising 
either  perception  or  will  through  any  other  organ  than  the 
brain.  But  even  when  the  brain  is  thus  in  action,  it  appears 
to  be  the  medulla  oblongata  which  combines  the  several  re- 
spiratory muscles  to  act  together.  In  such  acts,  for  example, 
as  those  of  coughing  and  sneezing,  the  mind  first  perceives  the 
irritation  at  the  larynx  or  nose,  and  may  exercise  a  certain 
degree  of  will  in  determining  the  actions,  as  e.  g.,  in  the  taking 
of  the  deep  inspiration  which  always  precedes  them.  But  the 
mode  in  which  the  acts  are  performed,  and  the  combination  of 
muscles  to  effect  them,  are  determined  by  the  medulla  oblon- 
gata, independently  of  the  will,  and  have  the  peculiar  char- 
acter of  reflex  involuntary  movements,  in  being  always,  and 
without  practice  or  experience,  precisely  adapted  to  the  end  or 
purpose. 

In  these,  and  in  all  the  other  extraordinary  respiratory 
actions,  such  as  are  seen  in  dyspnoea,  or  in  straining,  yawning, 
hiccough,  and  others,  the  medulla  oblongata  brings  into 
adapted  combination  of  action  many  other  muscles  besides 
those  commonly  exerted  in  respiration.  Almost  all  the  muscles 
of  the  body,  in  violent  efforts  of  dyspnoea,  coughing,  and  the 
like,  may  be  brought  into  action  at  once,  or  in  quick  succes- 
sion ;  but  more  particularly  the  muscles  of  the  larynx,  face, 
scapula,  spine,  and  abdomen,  co-operate  in  these  efforts  with 
the  muscles  of  the  chest.  These,  therefore,  are  often  classed 


186  RESPIRATION. 

as  secondary  muscles  of  respiration  ;  and  the  nerves  supplying 
them,  including  especially  the  facial,  pneumogastric,  spinal 
accessory,  and  external  respiratory  nerves,  were  classed  by  Sir 
Charles  Bell  with  the  phrenic,  as  the  respiratory  system  of 
nerves.  There  appears,  however,  no  propriety  in  making  a 
separate  system  of  these  nerves,  since  their  mode  of  action  is 
not  peculiar,  and  many  besides  them  co-operate  in  the  respira- 
tory acts.  That  which  is  peculiar  in  the  nervous  influence, 
directing  the  extraordinary  movements  of  respiration,  is,  that 
so  many  nerves  are  combined  toward  one  purpose  by  the  power 
of  a  distinct  nervous  centre,  the  medulla  oblongata.  In  other 
than  respiratory  movements,  these  nerves  may  act  singly  or 
together,  without  the  medulla  oblongata ;  but  after  it  is  de- 
stroyed, no  movement  adapted  to  respiration  can  be  performed 
by  any  of  the  muscles,  even  though  the  part  of  the  spinal  cord 
from  which  they  arise  be  perfect.  The  phrenic  nerves,  for 
example,  are  unable  to  excite  respiratory  movement  of  the 
diaphragm  when  their  connection  with  the  medulla  oblongata 
is  cut  off,  though  their  connection  with  the  spinal  cord  may  be 
uninjured.1 

Effects  of  the  Suspension  and  Arrest  of  Respiration. 

These  deserve  some  consideration,  because  of  the  illustra- 
tion which  they  afford  of  the  nature  of  the  normal  processes 
of  respiration  and  circulation.  When  the  process  of  respira- 
tion is  stopped,  either  by  arresting  the  respiratory  movements, 
or  permitting  them  to  continue  in  an  atmosphere  deprived  of 
uncombined  oxygen,  the  circulation  of  blood  through  the  lungs 
is  retarded,  and  at  length  stopped.  The  immediate  effect  of 
such  retarded  circulation  is  an  obstruction  to  the  exit  of  blood 
from  the  right  ventricle :  this  is  followed  by  delay  in  the  re- 
turn of  venous  blood  to  the  heart ;  and  to  this  succeeds  venous 
congestion  of  the  nervous  centres  and  all  the  other  organs  of 
the  body.  In  such  retardation,  also,  an  unusually  small 
supply  of  blood  is  transmitted  through  the  lungs  to  the  left 
side  of  the  heart ;  and  this  small  quantity  is  venous. 

The  condition,  then,  in  which  a  suffocated,  or  asphyxiated 
animal  dies  is,  commonly,  that  the  left  side  of  the  heart  is 
nearly  empty,  while  the  lungs,  right  side  of  the  heart,  and 
other  organs,  are  gorged  with  venous  blood.  To  this  condi- 
tion many  things  contribute.  1st.  The  obstructed  passage  of 

1  The  influence  of  the  nervous  system  in  respiration  will  be  again 
and  more  particularly  considered  in  the  section  treating  of  the  me- 
dulla oblongata  and  pneumogastric  nerves. 


SUSPENDED    ANIMATION.  187 

blood  through  the  lungs,  which  appears  to  be  the  first  of  the 
events  leading  to  suffocation,  seems  to  depend  on  the  cessation 
of  the  interchange  of  gases,  as  if  blood  charged  with  carbonic 
acid  could  not  pass  freely  through  the  pulmonary  capillaries. 
But  the  stagnation  of  blood  in  the  pulmonary  capillaries 
would  not,  perhaps,  be  enough  to  stop  entirely  the  circulation, 
unless  the  action  of  the  heart  were  also  weakened.  There- 
fore, 2dly,  the  fatal  result  is  probably  due,  in  some  measure, 
to  the  enfeebled  action  of  the  right  side  of  the  heart,  in  conse- 
quence of  its  overdistension  by  blood  continually  flowing  into 
it ;  this  flow,  probably,  being  much  increased  by  the  powerful 
but  fruitless  efforts  continually  made  at  inspiration  (Eccles). 
And  3dly,  because  of  the  obstruction  at  the  right  side  of  the 
heart,  there  must  be  venous  congestion  in  the  medulla  oblon- 
gata  and  nervous  centres :  and  this  evil  is  augmented  by  the 
left  ventricle  receiving  and  propelling  none  but  venous  blood. 
Hence,  slowness  and  disorder  of  the  respiratory  movements 
and  of  the  movements  of  the  heart  may  be  added.  Under  all 
these  conditions  combined,  the  heart  at  length  ceases  to  act ; 
the  cessation  of  its  action  being  also  in  great  measure,  proba- 
bly, brought  about,  4thly,  by  the  imperfect  supply  of  oxyge- 
nated blood  to  its  muscular  tissue. 

In  some  experiments  performed  by  a  committee  appointed 
by  the  Medico-Chirurgical  Society  to  investigate  the  subject  of 
Suspended  Animation,  it  was  found  that,  in  the  dog,  during 
simple  apnoaa,  i.  e.,  simple  privation  of  air,  as  by  plugging  the 
trachea,  the  average  duration  of  the  respiratory  movements 
after  the  animal  had'  been  deprived  of  air,  was  4  minutes  5 
seconds ;  the  extremes  being  3  minutes  30  seconds,  and  4 
minutes  40  seconds.  The  average  duration  of  the  heart's  ac- 
tion, on  the  other  hand,  was  7  minutes  11  seconds;  the  ex- 
tremes being  6  minutes  40  seconds,  and  7  minutes  45  seconds. 
It  would  seem,  therefore,  that  on  an  average,  the  heart's  action 
continues  for  3  minutes  15  seconds  after  the  animal  has  ceased 
to  make  respiratory  efforts.  A  very  similar  relation  was  ob- 
served in  the  rabbit.  Recovery  never  took  place  after  the 
heart's  action  had  ceased. 

The  results  obtained  by  the  committee  on  the  subject  of 
drowning  were  very  remarkable,  especially  in  this  respect,  that 
whereas  an  animal  may  recover,  after  simple  deprivation  of 
air  for  nearly  four  minutes,  yet,  after  submersion  in  water  for 
li  minutes,  recovery  seems  to  be  impossible.  This  remark- 
able difference  was  found  to  be  due,  not  to  the  mere  submer- 
sion, nor  directly  to  the  struggles  of  the  animal,  nor  to  depres- 
sion of  temperature,  but  to  the  two  facts,  that  in  drowning,  a 
free  passage  is  allowed  to  air  out  of  the  lungs,  and  a  free  en- 


188  RESPIRATION. 

trance  of  water  into  them.  In  proof  of  the  correctness  of  this 
explanation  it  was  found  that  when  two  dogs  of  the  same  size, 
one,  however,  having  his  windpipe  plugged,  the  other  not,  were 
submerged  at  the  same  moment,  and  taken  out  after  being 
under  water  for  2  minutes,  the  former  recovered  on  removal 
of  the  plug,  the  latter  did  not.  It  is  probably  to  the  entrance 
of  water  into  the  lungs  that  the  speedy  death  in  drowning  is 
mainly  due.  The  results  of  post-mortem  examination  strongly 
support  this  view.  On  examining  the  lungs  of  animals  de- 
prived of  air  by  plugging  the  trachea,  they  were  found  simply 
congested ;  but  in  the  animals  drowned,  not  only  was  the  con- 
gestion much  more  intense,  accompanied  with  ecchymosed 
points  on  the  surface  and  in  the  substance  of  the  lung,  but  the 
air-tubes  were  completely  choked  up  with  a  sanious  foam,  con- 
sisting of  blood,  water,  and  mucus,  churned  up  with  the  air  in 
the  lungs  by  the  respiratory  efforts  of  the  animal.  The  lung- 
substance,  too,  appeared  to  be  saturated  and  sodden  with  water, 
which,  stained  slightly  with  blood,  poured  out  at  any  point 
where  a  section  was  made.  The  lung  thus  sodden  with  water 
was  heavy  (though  it  floated),  doughy,  pitted  on  pressure,  and 
was  incapable  of  collapsing.  It  is  not  difficult  to  understand 
how,  by  such  infarction  of  the  tubes,  air  is  debarred  from  reach- 
ing the  pulmonary  cells :  indeed  the  inability  of  the  lungs  to 
collapse  on  opening  the  chest  is  a  proof  of  the  obstruction 
which  the  froth  occupying  the  air-tubes  offers  to  the  transit  of 
air.  The  entire  dependence  of  the  early  fatal  issue,  in  apnoea 
by  drowning,  upon  the  open  condition  of  the  windpipe,  and  its 
results,  was  also  strikingly  shown  by  'the  following  experi- 
ment. A  strong  dog  had  its  windpipe  plugged,  and  was  then 
.submerged  in  water  for  four  minutes ;  in  three-quarters  of  a 
minute  after  its  release  it  began  to  breathe,  and  in  four  minutes 
had  fully  recovered.  This  experiment  was  repeated  with  sim- 
ilar results  on  other  dogs.  When  the  entrance  of  water  into 
the  lungs,  and  its  drawing  up  with  the  air  into  the  bronchial 
tubes  by  means  of  the  respiratory  efforts,  were  diminished,  as 
by  rendering  the  animal  insensible  by  chloroform  previously 
to  immersion,  and  thus  depriving  it  of  the  power  of  making 
violent  respiratory  efforts,  it  was  found  that  it  could  bear  im- 
mersion for  a  longer  period  without  dying  than  when  not  thus 
rendered  insensible.  Probably  to  a  like  diminution  in  the 
respiratory  efforts,  may  also  be  ascribed  the  greater  length  of 
time  persons  have  been  found  to  bear  submersion  without 
being  killed,  when  in  a  state  of  intoxication,  poisoning  by  nar- 
cotics, or  during  insensibility  from  syncope. 

It  is  to  the  accumulation  of  carbonic  acid  in  the  blood,  and 
its  conveyance  into  the  organs,  that  we  must,  in  the  first  place, 


ANIMAL     HEAT.  189 

ascribe  the  phenomena  of  asphyxia.  For  when  this  does  not 
happen,  all  the  other  conditions  may  exist  without  injury;  as 
they  do,  for  example,  in  hibernating  warm-blooded  animals. 
In  these,  life  is  supported  for  many  months  in  atmospheres  in 
which  the  same  animals,  in  their  full  activity,  would  be  speedily 
suffocated.  During  the  periods  of  complete  torpor,  their  respi- 
ration almost  entirely  ceases ;  the  heart  acts  very  slowly  and 
feebly ;  the  processes  of  organic  life  are  all  but  suspended,  and 
the  animal  may  be  with  impunity  completely  deprived  of 
atmospheric  air  for  a  considerable  period.  Spallanzani  kept 
a  marmot,  in  this  torpid  state,  immersed  for  four  hours  in  car- 
bonic acid  gas,  without  its  suffering  any  apparent  inconveni- 
ence. Dr.  Marshall  Hall  kept  a  lethargic  bat  under  water 
for  16  minutes,  and  a  lethargic  hedgehog  for  22&  minutes ;  and 
neither  of  the  animals  appeared  injured  by  the  experiment. 


CHAPTER  VIII. 

ANIMAL  HEAT. 

THE  average  temperature  of  the  human  body  in  those  in- 
ternal parts  which  are  more  easily  accessible,  as  the  mouth 
and  rectum,  is  from  98.5°  to  99.5°  F. 

In  different  parts  of  the  external  surface  of  the  human  body 
the  temperature  varies  only  to  the  extent  of  two  or  three  de- 
grees, when  all  are  alike  protected  from  cooling  influences  ; 
and  the  difference  which  under  these  circumstances  exists, 
depends  chiefly  upon  the  different  degrees  of  blood-supply. 
In  the  arm-pit — the  most  convenient  situation,  under  ordinary 
circumstances,  for  examination  by  the  thermometer — the  aver- 
age temperature  is  98. 6 D  F. 

The  chief  circumstances  by  which  the  temperature  of  the 
healthy  body  is  influenced  are  the  following : 

Age. — The  average  temperature  of  the  new-born  child  is  only 
about  1°  F.  above  that  proper  to  the  adult ;  and  the  difference 
becomes  still  more  trifling  during  infancy  and  early  childhood. 
According  to  Wunderlich,  the  temperature  falls  to  the  extent 
of  about  -J-0  to  £°  F.  from  early  infancy  to  puberty,  and  by 
about  the  same  amount  from  puberty  to  fifty  or  sixty  years 
of  age.  In  old  age  the  temperature  again  rises,  and  approaches 
that  of  infancy. 

Although  the  average  temperature  of  the  body,  however, 


190  ANIMAL    HEAT. 

is  not  lower  than  that  of  younger  persons,  yet  the  power  of 
resisting  cold  is  less  in  them — exposure  to  a  low  temperature 
causing  a  greater  reduction  of  heat  than  in  young  persons. 

The  same  rapid  diminution  of  temperature  was  observed  by 
M.  Edwards  in  the  new-born  young  of  most  carnivorous  and 
rodent  animals  when  they  were  removed  from  the  parent,  the 
temperature  of  the  atmosphere  being  between  50°  and  53$° 
F. ;  whereas,  while  lying  close  to  the  body  of  the  mother, 
their  temperature  was  only  2  or  3  degrees  lower  than 
hers.  The  same  law  applies  to  the  young  of  birds.  Young 
sparrows,  a  week  after  they  were  hatched,  had  a  temperature 
of  95°  to  97°,  while  in  the  nest ;  but  when  taken  from  it,  their 
temperature  fell  in  one  hour  to  66£°,  the  temperature  of  the 
atmosphere  being  at  the  time  622°.  It  appears  from  his  in- 
vestigations, that  in  respect  of  the  power  of  generating  heat, 
some  Mammalia  are  born  in  a  less  developed  condition  than 
others  ;  and  that  the  young  of  dogs,  cats,  and  rabbits,  for 
example,  are  inferior  to  the  young  of  those  animals  which  are 
not  born  blind.  The  need  of  external  warmth  to  keep  up 
the  temperature  of  new-born  children  is  well  known  ;  the  re- 
searches of  M.  Edwards  show  that  the  want  of  it  is,  as  Hunter 
suggested,  a  much  more  frequent  cause  of  death  in  new-born 
children  than  is  generally  supposed,  and  furnish  a  strong  argu- 
ment against  the  idea,  that  children,  by  early  exposure  to 
cold,  can  soon  be  hardened  into  resisting  its  injurious  influ- 
ence. 

Sex. — The  average  temperature  of  the  female  would  appear 
from  observations  by  Dr.  Ogle  to  be  very  slightly  higher  than 
that  of  the  male. 

Period  of  the  Day. — The  temperature  undergoes  a  gradual 
alteration,  to  the  extent  of  about  1°  to  1^°  F.  in  the  course  of 
the  day  and  night ;  the  minimum  being  at  night  or  in  the  early 
morning,  the  maximum  late  in  the  afternoon. 

Exercise. — Active  exercise  raises  the  temperature  of  the  body. 
This  may  be  partly  ascribed  to  the  fact,  that  every  muscular 
contraction  is  attended  by  the  development  of  one  or  two  de- 
grees of  heat  in  the  acting  muscle ;  and  that  the  heat  is  in- 
creased according  to  the  number  and  rapidity  of  these  con- 
tractions, and  is  quickly  diffused  by  the  blood  circulating  from 
the  heated  muscles.  Possibly,  also,  some  heat  may  be  gene- 
rated in  the  various  movements,  stretchings,  and  recoilings  of 
the  other  tissues,  as  the  arteries,  whose  elastic  walls,  alternately 
dilated  and  contracted,  may  give  out  some  heat,  just  as  caout- 
chouc alternately  stretched  and  recoiling  becomes  hot.  But 
the  heat  thus  developed  cannot  be  great. 

Moreover,  the  increase  of  temperature  throughout  the  whole 


TEMPERATUKE    OF    THE     BODY.  191 

body,  produced  by  active  exercise,  is  but  small ;  the  great  ap- 
parent increase  of  heat  depending,  in  a  great  measure,  on  the 
increased  circulation  and  quantity  of  blood,  and,  therefore, 
greater  heat,  in  parts  of  the  body  (as  the  skin,  and  especially 
the  skin  of  the  extremities),  which,  at  the  same  time  that  they 
feel  more  acutely  than  others  any  changes  of  temperature  are, 
under  ordinary  conditions,  by  some  degrees  colder  than  organs 
more  centrally  situated. 

That  the  increased  temperature  of  the  skin  during  exercise 
is  not  accompanied  by  a  proportional  increase  of  the  heat  of 
other  parts,  which  are  naturally  much  warmer,  is  well  shown 
by  some  observations  of  Dr.  J.  Davy. 

Climate  and  Season. — In  passing  from  a  temperate  to  a 
hot  climate  the  temperature  of  the  human  body  rises  slightly, 
the  increase  rarely  exceeding  2°  to  3°  F.  In  summer  the 
temperature  of  the  body  is  a  little  higher  than  in  winter ;  the 
difference  amounting  to  from  ^°  to  £°  F.  (Wunderlich.) 

The  same  effects  are  observable  in  alterations  of  tempera- 
ture not  depending  on  season  or  climate. 

Food  and  Drink. — The  effect  of  a  meal  upon  the  tempera- 
ture of  a  body  is  but  small.  A  very  slight  rise  usually  occurs. 

Cold  alcoholic  drinks  depress  the  temperature  somewhat 
(J°  to  1°  F.).  Warm  alcoholic  drinks,  as  well  as  warm  tea 
and  coffee,  raise  the  temperature  (about  £°  F.). 

In  disease  the  temperature  of  the  body  deviates  from  the 
normal  standard  to  a  greater  extent  than  would  be  anticipated 
from  the  slight  effect  of  external  conditions  during  health. 
Thus,  in  some  diseases,  as  pneumonia  and  typhus,  it  occasion- 
ally rises  as  high  as  106°  or  107°  F. ;  and  considerably  higher 
temperatures  have  been  noted.  In  a  case  of  malignant  fever 
recently  recorded  by  Mr.  Norman  Moore,  the  temperature  in 
the  axilla  rapidly  rose  to  111°  F. ;  when  the  patient  died. 
The  highest  temperature  recorded  in  a  living  man,  112.5°  F., 
was  observed  by  Wunderlich,  in  a  case  of  idiopathic  tetanus, 
at  the  time  of  death.  In  the  morbus  cceruleus,  in  which  there 
is  defective  arterialization  of  the  blood  from  malformation  of 
the  heart,  the  temperature  of  the  body  may  be  as  low  as  79° 
or  77J°  ;  in  Asiatic  cholera  a  thermometer  placed  in  the  mouth 
sometimes  rises  only  to  77°  or  79° ;  and  in  a  case  of  tubercular 
meningitis,  observed  by  Dr.  Gee,  the  temperature  of  the  rec- 
tum remained  for  hours  at  79.4°  F. 

The  temperature  maintained  by  Mammalia  in  an  active 
state  of  life  according  to  the  tables  of  Tiedemann  and  Kudolphi, 
averages  101°.  The  extremes  recorded  by  them  were  96°  and 
106 D,  the  former  in  the  narwhal,  the  latter  in  a  bat  (Vesper- 
tilio  pipistrella).  In  birds,  the  average  is  as  high  as  107° ; 


192  A  N  I  M  A  L    H  E  A  T. 

the  highest  temperature,  111.25°,  being  in  the  small  species, 
the  linnets,  &c.  Among  reptiles,  Dr.  John  Davy  found,  that 
while  the  medium  they  were  in  was  75°,  their  average  tem- 
perature was  82.5°.  As  a  general  rule,  their  temperature, 
though  it  falls  with  that  of  the  surrounding  medium,  is,  in 
temperate  media,  two  or  more  degrees  higher ;  and  though  it 
rises  also  with  that  of  the  medium,  yet  at  very  high  degrees  it 
ceases  to  do  so,  and  remains  even  lower  than  that  of  the  medium. 
Fish  and  Invertebrata  present,  as  a  general  rule,  the  same 
temperature  as  the  medium  in  which  they  live,  whether  that  be 
high  or  low ;  only  among  fish,  the  tunny  tribe,  with  strong 
hearts  and  red  meat-like  muscles,  and  more  blood  than  the 
average  offish  have,  are  generally  7°  warmer  than  the  water 
around  them. 

The  difference,  therefore,  between  what  are  commonly  called 
the  warm-  and  the  cold-blooded  animals,  is  not  one  of  abso- 
lutely higher  or  lower  temperature ;  for  the  animals  which  to 
us,  in  a  temperate  climate  feel  cold  (being  like  the  air  or 
water,  colder  than  the  surface  of  our  bodies),  would,  in  an  ex- 
ternal temperature  of  100°,  have  nearly  the  same  temperature 
and  feel  hot  to  us.  The  real  difference  is,  as  Mr.  Hunter  ex- 
pressed it,  that  what  we  call  warm-blooded  animals  (birds  and 
Mammalia),  have  a  certain  "permanent  heat  in  all  atmo- 
spheres," while  the  temperature  of  the  others,  which  we  call 
cold-blooded,  is  "variable  with  every  atmosphere." 

The  power  of  maintaining  a  uniform  temperature,  which 
Mammalia  and  birds  possess,  is  combined  with  the  want  of 
power  to  endure  such  changes  of  temperature  of  their  bodies 
as  are  harmless  to  the  other  classes ;  and  when  their  power  of 
resisting  change  of  temperature  ceases,  they  suffer  serious  dis- 
turbances or  die. 

Sources  and  Mode  of  Production  of  Heat  in  the  Body. 

In  explaining  the  chemical  changes  effected  in  the  process 
of  respiration  (p.  180 ),  it  was  stated  that  the  oxygen  of  the 
atmosphere  taken  into  the  blood  is  combined,  in  the  course  of 
the  circulation,  with  the  carbon  and  the  hydrogen  of  disin- 
tegrated and  absorbed  tissues,  and  of  certain* elements  of  food 
which  have  not  been  converted  into  tissues.  That  such  a  com- 
bination between  the  oxygen  of  the  atmosphere  and  the  carbon 
and  hydrogen  in  the  blood,  is  continually  taking  place,  is 
made  certain  by  the  fact,  that  a  larger  amount  of  carbon  and 
hydrogen  is  constantly  being  added  to  the  blood  from  the  food 
than  is  required  for  the  ordinary  purposes  of  nutrition,  and 
that  a  quantity  of  oxygen  is  also  constantly  being  absorbed 


PRODUCTION    OF    HEAT.  193 

from  the  air  in  the  luags,  of  the  disposal  of  which  no  account 
can  be  given  except  by  regarding  it  as  combining,  for  the 
most  part,  with  the  excess  of  carbon  and  hydrogen,  and  being 
excreted  in  the  form  of  carbonic  acid  and  water.  In  other 
words,  the  blood  of  warm-blooded  animals  appears  to  be  always 
receiving  from  the  digestive  canal  and  the  lungs  more  carbon, 
hydrogen,  and  oxygen  than  are  consumed  in  the  repair  of  the 
tissues,  and  to  be  always  emitting  carbonic  acid  and  water,  for 
which  there  is  no  other  known  source  than  the  combination  of 
these  elements.1  By  such  combination,  heat  is  continually 
produced  in  the  animal  body.  The  same  amount  of  heat  will 
be  evolved  in  the  union  of  any  given  quantities  of  carbon  and 
oxygen,  and  of  hydrogen  and  oxygen,  whether  the  combina- 
tion be  rapid  and  evident,  as  in  ordinary  combustion,  or  slow 
and  imperceptible,  as  in  the  changes  which  occur  in  the  living 
body.  And  since  the  heat  thus  arising  will  be  generated  wher- 
ever the  blood  is  carried,  every  part  of  the  body  will  be  heated 
equally,  or  nearly  so. 

This  theory,  that  the  maintenance  of  the  temperature  of  the 
living  body  depends  on  continual  chemical  change,  chiefly  by 
oxidation,  of  combustible  materials  existing  in  the  tissues  and 
in  the  blood,  has  long  been  established  by  the  demonstration 
that  the  quantity  of  carbon  and  hydrogen  which,  in  a  given 
time,  unites  in  the  body  with  oxygen,  is  sufficient  to  account 
for  the  amount  of  heat  generated  in  the  animal  within  the 
same  time ;  an  amount  capable  of  maintaining  the  temperature 
of  the  body  at  from  98°  to  100°,  notwithstanding  a  large  loss 
by  radiation  and  evaporation. 

Many  things  observed  in  the  economy  and  habits  of  animals 
are  explicable  by  this  theory,  and  may  here  briefly  be  quoted, 
although  no  longer  required  as  additional  evidence  for  its 
truth.  Thus,  as  a  general  rule,  in  the  various  classes  of  ani- 
mals, as  well  as  in  individual  examples  of  each  class,  the 
quantity  of  heat  generated  in  the  body  is  in  direct  proportion 
to  the  activity  of  the  respiratory  process.  The  highest  animal 
temperature,  for  example,  is  found  in  birds,  in  whom  the  func- 
tion of  respiration  is  most  actively  performed.  In  Mammalia, 
the  process  of  respiration  is  less  active,  and  the  average  tem- 
perature of  the  body  less,  than  in  birds.  In  reptiles,  both  the 
respiration  and  the  heat  are  at  a  much  lower  standard ;  while 
in  animals  below  them,  in  which  the  function  of  respiration  is 
at  the  lowest  point,  a  power  of  producing  heat  is,  in  ordinary 

1  Some  heat  will  also  be  generated  in  the  combination  of  sulphur 
and  phosphorus  with  oxygen,  to  which  reference  has  been  made 
(p.  177)  ;  but  the  amount  thus  produced  is  but  small. 


194  A  N  I  M  A  L     H  E  A  T. 

circumstances,  hardly  discernible.  Among  these  lower  ani- 
mals, however,  the  observations  of  Mr.  Newport  supply  con- 
firmatory evidence.  He  shows  that  the  larva,  in  which  the 
respiratory  organs  are  smaller  in  comparison  with  the  size  of 
the  body,  has  a  lower  temperature  than  the  perfect  insect. 
Volant  insects  have  the  highest  temperature,  and  they  have 
always  the  largest  respiratory  organs  and  breathe  the  greatest 
quantity  of  air;  while  among  terrestrial  insects,  those  also 
produce  the  most  heat  which  have  the  largest  respiratory  or- 
gans and  breathe  the  most  air.  During  sleep,  hibernation, 
and  other  states  of  inaction,  respiration  is  slower  or  suspended, 
and  the  temperature  is  proportionately  diminished ;  while,  on 
the  other  hand,  when  the  insect  is  most  active  and  respiring 
most  voluminously,  its  amount  of  temperature  is  at  its  maxi- 
mum, and  corresponds  with  the  quantity  of  respiration. 
Neither  the  rapidity  of  the  circulation,  nor  the  size  of  the 
nervous  system,  according  to  Mr.  Newport,  presents  such  a 
constant  relation  to  the  evolution  of  heat. 

On  the  Regulation  of  the  Temperature  of  the  Human  Body. 

The  continual  production  of  heat  in  the  body  has  been 
already  referred  to.  There  is  also,  of  necessity,  a  continual 
loss.  But  in  healthy,  warm-blooded  animals,  as  already  re- 
marked, the  loss  and  gain  of  heat  are  so  nearly  balanced  one 
by  the  other,  that  under  all  ordinary  circumstances,  a  uni- 
form temperature,  within  two  or  three  degrees,  is  preserved. 

The  loss  of  heat  from  the  human  body  takes  place  chiefly 
by  radiation  and  conduction  from  its  surface,  and  by  means 
of  the  constant  evaporation  of  water  from  the  same  part,  and 
from  the  air-passages.  In  each  act  of  respiration,  heat  is  also 
lost  by  so  much  warmth  as  the  expired  air  acquires  (p.  173). 
All  food  and  drink  which  enter  the  body  at  a  lower  tempera- 
ture than  itself,  abstract  a  small  measure  of  heat,  and  the 
urine  and  faeces  take  about  a  like  amount  away,  when  they 
leave  the  body.  Lastly,  some  part  of  the  heat  of  the  body  is 
rendered  imperceptible,  and  therefore  lost  as  heat,  by  being 
manifested  in  the  form  of  mechanical  motion. 

By  far  the  most  important  loss  of  heat  from  the  body, — 
probably  80  or  90  per  cent,  of  the  whole  amount, — is  that 
which  proceeds  from  radiation,  conduction,  and  evaporation 
from  the  skin.  And  it  is  to  this  part  especially,  and  in  a 
smaller  measure  to  the  air-passages,  that  we  must  look  for  the 
means  by  which  the  temperature  is  regulated ;  in  other  words, 
by  which  it  is  prevented  from  rising  beyond  the  normal  point 
on  the  one  hand,  or  sinking  below  it  on  the  other.  The  chief 


REGULATION    OF    THE    TEMPERATURE.      195 

indirect  means  for  accomplishing  the  same  end  are,  variations 
in  the  amount  and  quality  of  the  food  and  drink  taken,  varia- 
tions in  clothing,  and  in  exposure  to  external  heat  or  cold. 

In  order  to  understand  the  means  by  which  the  heat  of  the 
body  is  regulated,  it  is  necessary  to  take  into  consideration  the 
following  facts :  First,  the  immediate  source  of  heat  in  the 
body  is  the  presence  of  a  large  quantity  of  a  warm  fluid — the 
blood,  the  temperature  of  which  is,  in  health,  about  100°  F. 
In  the  second  place,  the  blood,  while  constantly  moving  in  a 
multitude  of  different  streams,  is,  every  minute  or  so,  gathered 
up  in  the  heart  into  one  large  stream,  before  being  again  dis- 
persed to  all  parts  of  the  body.  In  this  way,  the  temperature 
of  the  blood  remains  almost  exactly  the  same  in  all  parts  ;  for 
while  a  portion  of  it  in  passing  through  one  organ,  as  the  skin, 
may  become  cooler,  and  through  another  organ,  as  the  liver, 
may  become  warmer,  the  effect  on  each  separate  stream  is  more 
or  less  neutralized  when  it  mingles  with  another,  and  an  aver- 
age is  struck,  so  to  speak,  for  all  the  streams  when  they  form 
one,  in  passing  through  the  heart. 

The  means,  by  which  the  skin  is  able  to  act  as  one  of  the 
most  important  organs  for  regulating  the  temperature  of  the 
blood,  are — (1)  that  it  offers  a  large  surface  for  radiation,  con- 
duction, and  evaporation ;  (2)  that  it  contains  a  large  amount 
of  blood ;  (3)  that  the  quantity  of  blood  contained  in  it  is  the 
greater  under  those  circumstances  which  demand  a  loss  of  heat 
from  the  body,  and  vice  versa.  For  the  circumstance  which 
directly  determines  the  quantity  of  blood  in  the  skin,  is  that 
which  governs  the  supply  of  blood  to  all  the  tissues  and  organs 
of  the  body,  namely,  the  power  of  the  vaso-motor  nerves  to 
cause  a  greater  or  less  tension  of  the  muscular  element  in  the 
walls  of  the  arteries  (see  p.  121),  and,  in  correspondence  with 
this,  a  lessening  or  increase  of  the  calibre  of  the  vessel  accom- 
panied by  a  less  or  greater  current  of  blood.  A  warm  or  hot 
atmosphere  so  acts  on  the  nerve-fibres  of  the  skin,  as  to  lead 
them  to  cause  in  turn  a  relaxation  of  the  muscular  fibre  of  the 
bloodvessels ;  and,  as  a  result,  the  skin  becomes  full-blooded, 
hot,  and  sweating ;  and  much  heat  is  lost.  With  a  low  tem- 
perature, on  the  other  hand,  the  bloodvessels  shrink,  and  in 
accordance  with  the  consequently  diminished  blood  supply,  the 
skin  becomes  pale,  and  cold,  and  dry.  Thus,  by  means  of  a 
self-regulating  apparatus,  the  skin  becomes  the  most  important 
of  the  means  by  which  the  temperature  of  the  body  is  regu- 
lated. 

In  connection  with  loss  of  heat  by  the  skin,  reference  has 
been  made  to  that  which  occurs  both  by  radiation  and  conduc- 
tion, and  by  evaporation ;  and  the  subject  of  animal  heat  has 


196  ANIMAL    HEAT. 

been  considered  almost  solely  with  regard  to  the  ordinary  case 
of  man  living  in  a  medium  colder  than  his  body,  and  therefore 
losing  heat  in  all  the  ways  mentioned.  The  importance  of  the 
means,  however,  adopted,  so  to  speak,  by  the  skin  for  regulat- 
ing the  temperature  of  the  body,  will  depend  on  the  conditions 
by  which  it  is  surrounded ;  an  inverse  proportion  existing  in 
most  cases  between  the  loss  by  radiation  and  conduction  on  the 
one  hand,  and  by  evaporation  on  the  other.  Indeed,  the  small 
loss  of  heat  by  evaporation  in  cold  climates  may  go  far  to  com- 
pensate for  the  greater  loss  by  radiation  ;  as,  on  the  other  hand, 
the  great  amount  of  fluid  evaporated  in  hot  air  may  remove 
nearly  as  much  heat  as  is  commonly  lost  by  both  radiation  and 
evaporation  in  ordinary  temperatures  ;  and  thus,  it  is  possible, 
that  the  quantities  of  heat  required  for  the  maintenance  of  a 
uniform  proper  temperature  in  various  climates  and  seasons 
are  not  so  different  as  they,  at  first  thought,  seem. 

Many  examples  might  be  given  of  the  power  which  the 
body  possesses  of  resisting  the  effects  of  a  high  temperature, 
in  virtue  of  evaporation  from  the  skin. 

Sir  Charles  Blagden  and  others  supported  a  temperature 
varying  between  198°  and  211°  F.,  in  dry  air  for  several 
minutes ;  and  in  a  subsequent  experiment  he  remained  eight 
minutes  in  a  temperature  of  260°.  But  such  heats  are  not 
tolerable  when  the  air  is  moist  as  well  as  hot,  so  as  to  prevent 
evaporation  from  the  body.  M.  C.  James  states,  that  in  the 
vapor  baths  of  Nero  he  was  almost  suffocated  in  a  tempera- 
ture of  112°,  while  in  the  caves  of  Testaccio,  in  which  the  air 
is  dry,  he  was  but  little  incommoded  by  a.  temperature  of  176°. 
In  the  former,  evaporation  from  the  skin  was  impossible ;  in 
the  latter,  it  was,  probably,  abundant,  and  the  layer  of  vapor 
which  would  rise  from  all  the  surface  of  the  body  would,  by 
its  very  slow  conducting  power,  defend  it  for  a  time  from  the 
full  action  of  the  external  heat. 

(The  glandular  apparatus,  by  which  secretion  of  fluid  from 
the  skin  is  effected,  will  be  considered  in  the  section  on  the 
Skin.) 

The  ways  by  which  the  skin  may  be  rendered  more  efficient 
as  a  cooling-apparatus  by  exposure,  by  baths,  and  by  other 
means,  which  man  instinctively  adopts  for  lowering  his  tem- 
perature when  necessary,  are  too  well  known  to  need  more  than 
to  be  mentioned. 

As  a  means  for  lowering  the  temperature,  the  lungs  and  air- 
passages  are  very  inferior  to  the  skin ;  although,  by  giving 
heat  to  the  air  we  breathe,  they  stand  next  to  the  skin  in  im- 
portance. As  a  regulating  power,  the  inferiority  is  still  more 
marked.  The  air  which  is  expelled  from  the  lungs  leaves  the 


REGULATION    OF    HEAT.  197 

body  at  about  the  temperature  of  the  blood,  and  is  always 
saturated  with  moisture.  No  inverse  proportion,  therefore, 
exists  between  the  loss  of  heat  by  radiation  and  conduction  on 
the  one  hand,  and  by  evaporation  on  the  other.  The  colder 
the  air,  for  example,  the  greater  will  be  the  loss  in  all  ways. 
Neither  is  the  quantity  of  blood  which  is  exposed  to  the  cool- 
ing influence  of  the  air  diminished  or  increased,  so  far  as  is 
known,  in  accordance  with  any  need  in  relation  to  temperature. 
It  is  true  that  by  varying  the  number  and  depth  of  the  respi- 
rations, the  quantity  of  heat  given  off  by  the  lungs  may  be 
made,  to  some  extent,  to  vary  also.  But  the  respiratory  pas- 
sages, while  they  must  be  considered  important  means  by  which 
heat  is  lost,  are  altogether  subordinate  in  the  power  of  regu- 
lating the  temperature,  to  the  skin. 

It  may  seem  to  have  been  assumed,  in  the  foregoing  pages, 
that  the  only  regulating  apparatus  for  temperature  required 
by  the  human  body  is  one  that  shall,  more  or  less,  produce  a 
cooling  effect ;  and  as  if  the  amount  of  heat  produced  were 
always,  therefore,  in  excess  of  that  which  is  required.  Such  an 
assumption  would  be  incorrect.  We  have  the  power  of  regu- 
lating the  production  of  heat,  as  well  as  its  loss. 

In  food  we  have  a  means  for  elevating  our  temperature.  It 
is  the  fuel,  indeed,  on  which  animal  heat  ultimately  depends 
altogether.  Thus,  when  more  heat  is  wanted,  we  instinctively 
take  more  food,  and  take  such  kinds  of  it  as  are  good  for  com- 
bustion ;  while  everyday  experience  shows  the  different  power 
of  resisting  cold  possessed  by  the  well-fed  and  by  the  starved. 

In  northern  regions,  again,  and  in  the  colder  seasons  of  more 
southern  climes,  the  quantity  of  food  consumed  is  (speaking 
very  generally)  greater  than  that  consumed  by  the  same  men 
or  animals  in  opposite  conditions  of  climate  and  seasons.  And 
the  food  which  appears  naturally  adapted  to  the  inhabitants 
of  the  coldest  climates,  such  as  the  several  fatty  and  oily  sub- 
stances, abounds  in  carbon  and  hydrogen,  and  is  fitted  to  com- 
bine with  the  large  quantities  of  oxygen  which,  breathing  cold 
dense  air,  they  absorb  from  their  lungs. 

In  exercise,  again,  we  have  an  important  means  of  raising 
the  temperature  of  our  bodies  (p.  190). 

The  influence  of  external  coverings  for  the  body  must  not  be 
unnoticed.  In  warm-blooded  animals,  they  are  always  adapted, 
among  other  purposes,  to  the  maintenance  of  uniform  temper- 
ature ;  and  man  adapts  for  himself  such  as  are,  for  the  same 
purpose,  fitted  to  the  various  climates  to  which  he  is  exposed. 
By  their  means,  and  by  his  command  over  food  and  fire,  he 
maintains  his  temperature  on  all  accessible  parts  of  the  sur- 
face of  the  earth. 

17 


198  ANIMAL     HEAT. 

The  influence  of  the  nervous  system  in  modifying  the  produc- 
tion of  heat  has  been  already  referred  to.  The  experiments 
and  observations  which  best  illustrate  it  are  those  showing, 
first,  that  when  the  supply  of  nervous  influence  to  a  part  is 
cut  off,  the  temperature  of  that  part  falls  below  its  ordinary 
degree  ;  and,  secondly,  that  when  death  is  caused  by  severe  in- 
jury to,  or  removal  of,  the  nervous  centres,  the  temperature  of 
the  body  rapidly  falls,  even  though  artificial  respiration  be 
performed,  the  circulation  maintained,  and  to  all  appearance 
the  ordinary  chemical  changes  of  the  body  be  completely  ef- 
fected. It  has  been  repeatedly  noticed,  that  after  division  of 
the  nerves  of  a  limb,  its  temperature  falls  ;  and  this  diminution 
of  heat  has  been  remarked  still  more  plainly  in  limbs  deprived 
of  nervous  influence  by  paralysis.  For  example,  Mr.  Earle 
found  the  temperature  of  the  hand  of  a  paralyzed  arm  to  be 
70°,  while  the  hand  of  the  sound  side  had  a  temperature  of 
92°  F.  On  electrifying  the  paralyzed  limb,  the  temperature 
rose  to  77°.  In  another  case,  the  temperature  of  the  paralyzed 
finger  was  56°  F.,  while  that  of  the  unaffected  hand  was  62°. 

With  equal  certainty,  though  less  definitely,  the  influence  of 
the  nervous  system  on  the  production  of  heat,  is  shown  in  the 
rapid  and  momentary  increase  of  temperature,  sometimes 
general,  at  other  times  quite  local,  which  is  observed  in  states 
of  nervous  excitement ;  in  the  general  increase  of  warmth  of 
the  body,  sometimes  amounting  to  perspiration,  which  is  ex- 
cited by  passions  of  the  mind ;  in  the  sudden  rush  of  heat  to 
the  face,  which  is  not  a  mere  sensation ;  and  in  the  equally 
rapid  diminution  of  temperature  in  the  depressing  passions. 
But  none  of  these  instances  suffices  to  prove  that  heat  is  gen- 
erated by  mere  nervous  action,  independent  of  any  chemical 
change ;  all  are  explicable,  on  the  supposition  that  the  nervous 
system  alters,  by  its  power  of  controlling  the  calibre  of  the 
bloodvessels  (p.  121),  the  quantity  of  blood  supplied  to  apart; 
while  any  influence  which  the  nervous  system  may  have  in  the 
production  of  heat,  apart  from  this  influence  on  the  blood- 
vessels, is  an  indirect  one,  and  is  derived  from  its  power  of 
causing  nutritive  change  in  the  tissues,  which  may,  by  involv- 
ing the  necessity  of  chemical  action,  involve  the  production 
of  heat.  The  existence  of  nerves,  which  regulate  animal  heat 
otherwise  than  by  their  influence  in  trophic  (nutritive)  or 
vaso-motor  changes,  although  by  many  considered  probable,  is 
not  yet  proven. 

In  connection  with  the  regulation  of  animal  temperature, 
and  its  maintenance  in  health  at  the  normal  height,  it  is  in- 
teresting to  note  the  result  of  circumstances  too  powerful,  either 
in  raising  or  lowering  the  heat  of  the  body,  to  be  controlled  by 


FOOD.  199 

the  proper  regulating  apparatus.  Walther  found  that  rabbits 
and  dogs,  when  tied  to  a  board  and  exposed  to  a  hot  sun, 
reached  a  temperature  of  114.8°  F.,  and  then  died.  Cases  of 
sunstroke  furnish  us  with  similar  examples  in  the  case  of  man ; 
for  it  would  seem  that  here  death  ensues  chiefly  or  solely  from 
elevation  of  the  temperature.  In  a  case  related  by  Dr.  Gee, 
the  temperature  in  the  axilla  was  109.5°  F.;  and  in  many 
febrile  diseases  the  immediate  cause  of  death  appears  to  be  the 
elevation  of  the  temperature  to  a  point  inconsistent  with  the 
continuance  of  life. 

The  effect  of  mere  loss  of  bodily  temperature  in  man  is  less 
well  known  than  the  effect  of  heat. 

From  experiments  by  Walther,  it  appears  that  rabbits  can 
be  cooled  down  to  48°  F.  before  they  die,  if  artificial  respira- 
tion be  kept  up.  Cooled  down  to  64°  F.,  they  cannot  recover 
unless  external  warmth  be  applied  together  with  the  employ- 
ment of  artificial  respiration.  Rabbits  not  cooled  below  77° 
F.  recover  by  external  warmth  alone. 


CHAPTER  IX. 

DIGESTION. 

DIGESTION  is  the  process  by  which  those  parts  of  our  food 
which  may  be  employed  in  the  formation  and  repair  of  the 
tissues,  or  in  the  production  of  heat,  are  made  fit  to  be  absorbed 
and  added  to  the  blood. 

Food. 

Food  may  be  considered  in  its  relation  to  these  two  purposes, 
the  nutrition  of  the  tissues  and  the  production  of  heat.  But, 
under  the  first  of  these  heads  will  be  included  many  other 
allied  functions,  as,  for  example,  secretion  and  generation: 
and  under  the  second,  not  the  production  of  heat  only  as  such, 
but  of  all  the  other  forces  correlated  with  it,  which  are  mani- 
fested by  the  living  body. 

The  following  is  a  convenient  tabular  classification  of  the 
usual  and  more  necessary  kinds  of  food: 

NITROGENOUS : 

Proteids,  as  Albumen,  Casein,  Syntonin,  Gluten,  and  their  allies, 
and  Gelatin  (containing  Carbon,  Hydrogen,  Oxygen,  and  Nitrogen; 
some  of  them,  also  Sulphur  and  Phosphorus). 


200  DIGESTION. 

NON-NlTROGENOUS  : 

(1.)  Amyloids — Starch,  Sugar,  and  their  allies  (containing  Carbon, 
Hydrogen,  and  Oxygen). 

(2.)  Oils  and  Fats  (containing  Carbon,  Hydrogen,  and  Oxygen; 
the  Oxygen  in  much  smaller  proportion  than  in  Starch  or  Sugar). 

(3  )  Mineral  or  Saline  Matters,  as  Chloride  of  Sodium,  Phosphate 
of  Lime,  &i.-. 

(4  )  Water. 

Animals  cannot  subsist  on  any  but  organic  substances,  and 
these  must  contain  the  several  elements  and  compounds  which 
are  naturally  combined  with  them:  in  other  words,  not  even 
organic  compounds  are  nutritive  unless  they  are  supplied  in 
their  natural  state.  Pure  fibrin,  pure  gelatin,  and  other  prin- 
ciples purified  from  the  substances  naturally  mingled  with 
them,  are  incapable  of  supporting  life  for  more  than  a  brief 
time. 

Moreover,  health  .cannot  be  maintained  by  any  number  of 
substances  derived  exclusively  from  one  only  of  the  two  chief 
groups  of  alimentary  principles  mentioned  above.  A  mixture 
of  nitrogenous  and  non-nitrogenous  organic  substances,  together 
with  the  inorganic  principles  which  are  severally  contained  in 
them,  is  essential  to  the  well-being,  and,  generally,  even  to  the 
existence  of  an  animal.  The  truth  of  this  is  demonstrated  by 
experiments  performed  for  the  purpose,  and  is  illustrated  by 
the  composition  of  the  food  prepared  by  nature,  as  the  exclu- 
sive source  of  nourishment  to  the  young  of  Mammalia,  namely, 
milk. 

COMPOSITION  OF  MILK. 

Human.  Cows. 

Water, 890  858 

Solids,   .         .         .         .         .         .110  142 

1000  1000 

Casein, 35  68 

Butter, 25 

Sugar  (with  extractives),  48  30 

Salts,      ......  2  6 

110  142 

In  milk,  as  will  be  seen  from  the  preceding  table,  the  albu- 
minous group  of  aliments  is  represented  by  the  casein,  the 
oleaginous  by  the  butter,  the  aqueous  by  the  water,  the  sac- 
charine by  the  sugar  of  milk.  Among  the  salts  of  milk  are 
likewise  phosphate  of  lime,  alkaline,  and  other  salts,  and  a 
trace  of  iron;  so  that  it  may  be  briefly  said  to  include  all  the 
substances  which  the  tissues  of  the  growing  animal  need  for 


COMPOSITION    OF    EGGS.  201 

their  nutrition,  and  which  are  required  for  the  production  of 
animal  heat. 

The  yolk  and  albumen  of  eggs  are  in  the  same  relation  as 
food  for  the  embryos  of  oviparous  animals,  that  milk  is  to  the 
young  of  Mammalia,  and  afford  another  example  of  mixed 
food  being  provided  as  the  most  perfect  nutrition. 

COMPOSITION  OF  FOWLS'  EGGS. 

White.  Yolk. 

Water,         ....     80.0         .         .         .  53.73 

Albumen,    ....     15.5         .         .         .  17.47 

Mucus,        ....       4.5  Yellow  Oil,    .  28.75 

Salts, 4.0        ...       6.0 

Experiments  illustrating  the  same  principle  have  been  per- 
formed by  Magendie  and  others.  Dogs  were  fed  exclusively 
on  sugar  and  distilled  water.  During  the  first  seven  or  eight 
days  they  were  brisk  and  active,  and  took  their  food  and  drink 
as  usual ;  but  in  the  course  of  the  second  week,  they  began  to 
get  thin,  although  their  appetite  continued  good,  and  they  took 
daily  between  six  and  eight  ounces  of  sugar.  The  emaciation 
increased  during  the  third  week,  and  they  became  feeble,  and 
lost  their  activity  and  appetite.  At  the  same  time  an  ulcer 
formed  on  each  cornea,  followed  by  an  escape  of  the  humors 
of  the  eye  :  this  took  place  in  repeated  experiments.  The  ani- 
mals still  continued  to  eat  three  or  four  ounces  of  sugar  daily, 
but  became  at  length  so  feeble  as  to  be  incapable  of  motion, 
and  died  on  a  day  varying  from  the  thirty-first  to  the  thirty- 
fourth.  On  dissection,  their  bodies  presented  all  the  appear- 
ances produced  by  death  from  starvation;  indeed,  dogs  will 
live  almost  the  same  length  of  time  without  any  food  at  all. 

When  dogs  were  fed  exclusively  on  gum,  results  almost 
similar  to  the  above  ensued.  When  they  were  kept  on  olive 
oil  and  water,  all  the  phenomena  produced  were  the  same, 
except  that  no  ulceration  of  the  cornea  took  place :  the  effects 
were  also  the  same  with  butter.  Tiedemann  and  Gmelin  ob- 
tained very  similar  results.  They  fed  different  geese,  one  with 
sugar  and  water,  another  with  gum  and  water,  and  a  third 
with  starch  and  water.  All  gradually  lost  weight.  The  one 
fed  with  gum  died  on  the  sixteenth  day ;  that  fed  with  sugar 
on  the  twenty-second ;  the  third,  which  was  fed  with  starch  on 
the  twenty -fourth  ;  and  another  on  the  twenty-seventh  day ; 
having  lost,  during  these  periods,  from  one-sixth  to  one-half  of 
their  weight.  The  experiments  of  Chossat  and  Letellier  prove 
the  same ;  and  in  men,  the  same  is  shown  by  the  various  dis- 
eases to  which  they  who  consume  but  little  nitrogenous  food 
are  liable,  and  especially,  as  Dr.  Budd  has  shown  by  the  affec- 
tion of  the  cornea  which  is  observed  in  Hindoos  feeding  almost 


202  DIGESTION. 

exclusively  on  rice.  But  it  is  not  only  the  non-nitrogenous 
substances,  which,  taken  alone,  are  insufficient  for  the  mainte- 
nance of  health.  The  experiments  of  the  Academies  of  France 
and  Amsterdam  were  equally  conclusive  that  gelatin  alone  soon 
ceases  to  be  nutritive. 

Mr.  Savory's  observations  on  food  confirm  and  extend  the 
results  obtained  by  Magendie,  Chossat,  and  others.  They  show 
that  animals  fed  exclusively  on  non-nitrogenous  diet  speedily 
emaciate  and  die,  as  if  from  starvation ;  that  a  much  larger 
amount  of  urine  is  voided  by  those  fed  with  nitrogenous  than 
by  those  with  non-nitrogenous  food ;  and  that  animal  heat  is 
maintained  as  well  by  the  former  as  by  the  latter — a  fact 
which  proves  that  nitrogenous  elements  of  food,  as  well  as  non- 
nitrogenous,  may  be  regarded  as  calorifacient.  The  non-nitro- 
genous principles,  however,  he  believes  to  be  calorifacient  es- 
sentially, not  being  first  converted  into  tissue;  but  of  the 
nitrogenous,  he  believes  that  only  a  part  is  thus  directly  cal- 
orifacient, the  rest  being  employed  in  the  formation  of  tissue. 
Contrary  to  the  views  of  Liebig  and  Lehmann,  Savory  has 
shown  that,  while  animals  speedily  die  when  confined  to  non- 
nitrogenous  diet,  they  may  live  long  when  fed  exclusively  with 
nitrogenous  food. 

Man  is  supported  as  well  by  food  constituted  wholly  of  ani- 
mal substances,  as  by  that  which  is  formed  entirely  of  vegeta- 
ble matters,  on  the  condition,  of  course,  that  it  contain  a  mix- 
ture of  the  various  nitrogenous  and  non-nitrogenous  substances 
just  shown  to  be  essential  for  healthy  nutrition.  In  the  case 
of  carnivorous  animals,  the  food  upon  which  they  exist,  con- 
sisting as  it  does  of  the  flesh  and  blood  of  other  animals,  not 
onjy  contains  all  the  elements  of  which  their  own  blood  and 
tissues  are  composed,  but  contains  them  combined,  probably, 
in  the  same  forms.  Therefore,  little  more  may  seem  requisite, 
in  the  preparation  of  this  kind  of  food  for  the  nutrition  of  the 
body,  than  that  it  should  be  dissolved  and  conveyed  into  the 
blood  in  a  condition  capable  of  being  reorganized.  But  in 
the  case  of  the  herbivorous  animals,  which  feed  exclusively 
upon  vegetable  substances,  it  might  seem  as  if  there  would  be 
greater  difficulty  in  procuring  food  capable  of  assimilation 
into  their  blood  and  tissues.  But  the  chief  ordinary  articles 
of  vegetable  food  contain  substances  identical  in  composition 
with  the  albumen,  fibrin,  and  casein,  which  constitute  the 
principal  nutritive  materials  in  animal  food.  Albumen  is 
abundant  in  the  juices  and  seeds  of  nearly  all  vegetables ;  the 
gluten  which  exists,  especially  in  corn  and  other  seeds  of 
grasses  as  well  as  in  their  juices,  is  identical  in  composition 
with  fibrin,  and  is  often  named  vegetable  fibrin  ;  and  the  sub- 


STARVATION. 


203 


stance  named  legumen,  which  is  obtained  especially  from  peas, 
beans,  and  other  seeds  of  leguminous  plants,  and  from  the 
potato,  is  identical  with  the  casein  of  milk.  All  these  vegeta- 
ble substances  are,  equally  with  the  corresponding  animal 
principles,  and  in  the  same  manner,  capable  of  conversion  into 
blood  and  tissue  ;  and  as  the  blood  and  tissues  in  beth  classes 
of  animals  are  alike,  so  also  the  nitrogenous  food  of  both  may 
be  regarded  as,  in  essential  respects,  similar. 

It  is  in  the  relative  quantities  of  the  nitrogenous  and  non- 
nitrogenous  compounds  in  these  different  foods  that  the  differ- 
ence lies,  rather  than  in  the  presence  of  substances  in  one  of 
them  which  do  not  exist  in  the  other.  The  only  non-nitro- 
genous compounds  in  ordinary  animal  food  are  the  fat,  the 
saline  matters,  and  water,  and,  in  some  instances,  the  vegeta- 
ble matters  which  may  chance  to  be  in  the  digestive  canals  of 
such  animals  as  are  eaten  whole.  The  amount  of  these,  how- 
ever, is  altogether  much  less  than  that  of  the  non-nitrogenous 
substances  represented  by  the  starch,  sugar,  gum,  oil,  &c.,  in 
the  vegetable  food  of  herbivorous  animals. 

The  effects  of  total  deprivation  of  food  have  been  made  the 
subject  of  experiments  on  the  lower  animals,  and  have  been 
but  too  frequently  illustrated  in  man. 

(1.)  One  of  the  most  notable  effects  of  starvation,  as  might 
be  expected,  is  loss  of  weight ;  the  loss  being  greatest  at  first, 
as  a  rule,  but  afterwards  not  varying  very  much,  day  by  day, 
until  death  ensues.  Chossat  found  that  the  ultimate  propor- 
tional loss  was,  in  different  animals  experimented  on,  almost 
exactly  the  same ;  death  occurring  when  the  body  had  lost 
two-fifths  (forty  per  cent.)  of  its  original  weight. 

Different  parts  of  the  body  lose  weight  in  very  different  pro- 
portions. The  following  results  are  taken,  in  round  numbers, 
from  the  table  given  by  M.  Chossat : 


Fat  loses 

Blood,  . 

Spleen, 

Pancreas, 

Liver,   . 

Heart,  . 

Intestines, 

Muscles  of  locomotion, 

Stomach  loees, 

Pharynx,  (Esophagus, 

Skin,     . 

Kidneys, 

Respiratory  apparatus, 

Bones,    . 

Eyes,     . 

Nervous  system.  . 


93  per  cent. 

75 

71 

64 

52 

44 

42 

42 

39 

3t 


31 
22 
16 
10 
2 


(nearly). 


204  DIGESTION. 

(2.)  The  effect  of  starvation  on  the  temperature  of  the  vari- 
ous animals  experimented  on  by  Chossat  was  very  marked. 
For  some  time  the  variation  in  the  daily  temperature  was  more 
marked  than  its  absolute  and  continuous  diminution,  the  daily 
fluctuation  amounting  to  5°  or  6°  F.,  instead  of  1°  or  2°  F.,  as 
in  health..  But  a  short  time  before  death,  the  temperature 
fell  very  rapidly,  and  death  ensued  when  the  loss  had  amounted 
to  about  30°  F.  It  has  been  often  said,  and  with  truth, 
although  the  statement  requires  some  qualification,  that  death 
by  starvation  is  really  death  by  cold ;  for  not  only  has  it  been 
found  that  differences  of  time  with  regard  to  the  period  of  the 
fatal  result  are  attended  by  the  same  ultimate  loss  of  heat,  but 
the  effect  of  the  application  of  external  warmth  to  animals 
cold  and  dying  from  starvation,  is  more  effectual  in  reviving 
them  than  the  administration  of  food.  In  other  words,  an 
animal  exhausted  by  deprivation  of  nourishment  is  unable  so 
to  digest  food  as  to  use  it  as  fuel,  and  therefore  is  dependent 
for  heat  on  its  supply  from  without.  Similar  facts  are  often 
observed  in  the  treatment  of  exhaustive  diseases  in  man. 

(3.)  The  symptoms  produced  by  starvation  in  the  human 
subject  are  hunger,  accompanied,  or  it  may  be  replaced,  by 
pain,  referred  to  the  region  of  the  stomach  ;  insatiable  thirst ; 
sleeplessness  ;  general  weakness  and  emaciation.  The  exhala- 
tions both  from  the  lungs  and  skin  are  fetid,  indicating  the 
tendency  to  decomposition  which  belongs  to  badly-nourished 
tissues ;  and  death  occurs,  sometimes  after  the  additional  ex- 
haustion caused  by  diarrhoea,  often  with  symptoms  of  nervous 
disorder,  delirium,  or  convulsions. 

(4.)  In  the  human  subject  death  commonly  occurs  within 
six  to  ten  days  after  total  deprivation  of  food.  But  this  period 
may  be  considerably  prolonged  by  taking  a  very  small  quan- 
tity of  food,  or  even  water  only.  The  cases  so  frequently  re- 
lated of  survival  after  many  days,  or  even  some  weeks,  of 
abstinence,  have  been  due  either  to  the  last-mentioned  circum- 
stances, or  to  others  less  effectual,  which  prevented  the  loss  of 
heat  and  moisture.  Cases  in  which  life  has  continued  after 
total  abstinence  from  food  and  drink  for  many  weeks,  or 
months,  exist  only  in  the  imagination  of  the  vulgar. 

(5.)  The  appearances  presented  after  death  from  starvation 
are  those  of  general  wasting  and  bloodlessness,  the  latter  con- 
dition being  least  noticeable  in  the  brain.  The  stomach  and 
intestines  are  empty  and  contracted,  and  the  walls  of  the  latter 
usually  appear  remarkably  thinned  and  almost  transparent. 
The  usual  secretions  are  scanty  or  absent,  with  the  exception 
of  the  bile,  which,  somewhat  concentrated  usually  fills  the  gall- 
bladder. All  parts  of  the  body  readily  decompose. 


DAILY    LOSS   OF    CARBON    AND    NITROGEN.      205 

It  has  just  been  remarked  that  man  can  live  upon  animal 
matters  alone,  or  upon  vegetables.  The  structure  of  his  teeth, 
however,  as  well  as  experience,  seems  to  declare  that  he  is  best 
fitted  for  a  mixed  diet ;  and  the  same  inference  may  be  readily 
gathered  from  other  facts  and  considerations.  Thus,  the  food 
a  man  takes  into  his  body  daily,  represents  or  ought  to  repre- 
sent the  quantity  and  kind  of  matter  necessary  for  replacing 
that  which  is  dally  cast  out  by  the  way  of  lungs,  skin,  kidneys, 
and  other  organs.  To  find  out,  therefore,  the  quantity  and 
kind  of  food  necessary  for  a  healthy  man,  it  will,  evidently, 
be  the  best  plan  to  consider  in  the  first  place  what  he  loses  by 
excretion. 

For  the  sake  of  example,  we  may  now  take  only  two  ele- 
ments, carbon  and  nitrogen,  and  if  we  discover  what  amount 
of  these  is  respectively  discharged  in  a  given  time  from  the 
body,  we  shall  be  in  a  position  to  judge  what  kind  of  food 
will  most  readily  and  economically  replace  their  loss. 

The  quantity  of  carbon  daily  lost  from  the  body  amounts 
to  about  4500  grains,  and  of  nitrogen  300  grains ;  and  if  a 
man  could  be  fed  by  these  elements,  as  such,  the  problem 
would  be  a  very  simple  one ;  a  corresponding  weight  of  char- 
coal, and,  allowing  for  the  oxygen  in  it,  of  atmospheric  air, 
would  be  all  that  is  necessary.  But,  as  before  remarked,  an 
animal  can  live  only  upon  these  elements  when  they  are  ar- 
ranged in  a  particular  manner  with  others,  in  the  form  of  an 
organic  compound,  as  albumen,  starch,  and  the  like ;  and  the 
relative  proportion  of  carbon  to  nitrogen  in  either  of  these 
compounds  alone,  is  by  no  means  the  proportion  required  in 
the  diet  of  man.  The  amount,  4500  grains  of  carbon,  repre- 
sents about  fifteen  times  the  quantity  of  nitrogen  required  in 
the  same  period ;  and  in  albumen,  the  proportion  of  carbon  to 
nitrogen  is  only  as  3.5  to  1.  If  therefore,  a  man  took  into 
his  body,  as  food,  sufficient  albumen  to  supply  him  with  the 
needful  amount  of  carbon,  he  would  receive  more  than  four 
times  as  much  nitrogen  as  he  wanted ;  and  if  he  took  only 
sufficient  to  supply  him  with  nitrogen,  he  would  be  starved  for 
want  of  carbon.  It  is  plain,  therefore,  that  he  should  take 
with  the  albuminous  part  of  his  food,  which  contains  so  large 
a  relative  amount  of  nitrogen  in  proportion  to  the  carbon  he 
needs,  substances  in  which  the  nitrogen  exists  in  much  smaller 
quantities. 

Food  of  this  kind  is  provided  in  such  compounds  as  starch 
and  fat.  The  latter  indeed  as  it  exists  for  the  most  part  in 
considerable  amount  mingled  with  the  flesh  of  animals,  re- 
moves to  a  great  extent,  in  a  diet  of  animal  food,  the  difficulty 
which  would  otherwise  arise  from  a  deficiency  of  carbon — fat 

18 


206  DIGESTION. 

containing  a  large  relative  proportion  of  this  element,  and  no 
nitrogen. 

To  take  another  example ;  the  proportion  of  carbon  to  ni- 
trogen in  bread  about  30  to  1.  If  a  man's  diet  were  confined 
to  bread,  he  would  eat,  therefore,  in  order  to  obtain  the  requi- 
site quantity  of  nitrogen,  twice  as  much  carbon  as  is  neces- 
sary ;  and  it  is  evident,  that,  in  this  instance,  a  certain  quan- 
tity of  a  substance  with  a  large  relative  amount  of  nitrogen 
is  the  kind  of  food  necessary  for  redressing  the  balance. 

To  place  the  preceding  facts  in  a  tabular  form,  and  taking 
meat  as  an  example  instead  of  pure  albumen  :  meat  contains 
about  10  per  cent,  of  carbon,  and  rather  more  than  3  per  cent, 
of  nitrogen.  Supposing  a  man  to  take  meat  for  the  supply  of 
the  needful  carbon,  he  would  require  45,000  grains,  or  nearly 
6£  Ibs.  containing : 

Carbon,     ........     4500  grains. 

Nitrogen 1350      » 

Excess  of  Nitrogen  above  the  amount  required,     1500      " 

Bread  contains  about  30  per  cent,  of  carbon  and  1  per  cent, 
of  nitrogen. 

If  bread  alone,  therefore,  were  taken  as  food,  a  man  would 
require,  in  order  to  obtain  the  requisite  nitrogen,  30,000  grains, 
containing : 

Carbon, 9000  grains. 

Nitrogen, 300      " 

Excess  of  Carbon  above  the  amount  required,     4500      a 

But  a  combination  of  bread  and  meat  would  supply  much 
more  economically  what  was  necessary.  Thus : 

Carbon.  Nitrogen. 
15,000  grains  of  bread  (or  rather  more  than 

2  Ib).  contain    ......     4500  grs.  150  grs. 

5,000  grains  of  meat  (or  about  fib.)  contain  .       500     "  150   " 

5000  "  300  « 

So  that  f  Ib.  of  meat,  and  less  than  2  Ibs.  of  bread  would 
supply  all  the  needful  carbon  and  nitrogen  with  but  little 
waste. 

From  these  facts  it  will  be  plain  that  a  mixed  diet  is  the 
best  and  most  economical  food  for  man ;  and  the  result  of  ex- 
perience entirely  coincides  with  what  might  have  been  antici- 
pated on  theoretical  grounds  only. 

It  must  not  be  forgotten,  however,  that  the  value  of  certain 
foods  may  depend  quite  as  much  on  their  digestibility,  as  on 


NECESSITY    FOR    CHANGES    OF     DIET.         207 

the  relative  quantities  of  the  necessary  elements  which  they 
contain. 

In  actual  practice,  moreover,  the  quantity  and  kind  of  food 
to  be  taken  with  most  economy  and  advantage  cannot  be  set- 
tled for  each  individual,  only  by  considerations  of  the  exact 
quantities  of  certain  elements  that  are  required.  Much  will 
of  necessity  depend  on  the  habits  and  digestive  powers  of  the 
individual,  on  the  state  of  his  excretory  organs,  and  on  many 
other  circumstances.  Food  which  to  one  person  is  appropriate 
enough,  may  be  quite  unfit  for  another ;  and  the  changes  of 
diet  so  instinctively  practiced  by  all  to  whom  they  are  possi- 
ble, have  much  more  reliable  grounds  of  justification  than  any 
which  could  be  framed  on  theoretical  considerations  only. 

In  many  of  the  experiments  on  the  digestibility  of  various 
articles  of  food,  disgust  at  the  sameness  of  the  diet  may  have 
had  as  much  to  do  with  inability  to  consume  and  digest  it,  as 
the  want  of  nutritious  properties  in  the  substances  which  were 
experimented  on.  And  that  disease  may  occur  from  the  want 
of  particular  food,  is  well  shown  by  the  occurrence  of  scurvy 
when  fresh  vegetables  are  deficient,  and  its  rapid  cure  when 
they  are  again  eaten  :  and  the  disease  which  is  here  so  re- 
markably evident  in  its  symptoms,  causes,  and  cure,  is  matched 
by  numberless  other  ailments,  the  causes  of  which,  however, 
although  analogous,  are  less  exactly  known,  and  therefore  less 
easily  combated. 

With  regard  to  the  quantity,  too,  as  well  as  the  kind  of  food 
necessary,  there  will  be  much  diversity  in  different  individuals. 
Dr.  Dalton  believed,  from  some  experiments  which  he  per- 
formed, that  the  quantity  of  food  necessary  for  a  healthy  man, 
taking  free  exercise  in  the  open  air,  is  as  follows : 

Meat,     .         .  .  .16  ounces,  or  1.00  Ib.  avoird. 

Bread,   .     "  .  .  .19        "  1.19  "         " 

Butter  or  Fat,  .  3J      "  0.22  "         " 

Water,.         .  .  .     52  fluid  oz.      3.38  «         " 

The  quantity  of  meat,  however,  here  given  is  probably  more 
in  proportion  to  the  other  articles  of  diet  enumerated  than  is 
needful  for  the  majority  of  individuals  under  the  circum- 
stances stated. 


PASSAGE   OF    FOOD    THROUGH   THE   ALIMENTARY   CANAL. 

The  course  of  the  food  through  the  alimentary  canal  of  man 
will  be  readily  seen  from  the  accompanying  diagram  (Fig. 
66).  The  food  taken  into  the  mouth  passes  thence  through 
the  03sophagus  into  the  stomach,  and  from  this  into  the  small 


208  DIGESTION. 

and  large  intestine  successively ;  gradually  losing,  by  absorp- 
tion, the  greater  portion  of  its  nutritive  constituents.  The 
residue,  together  with  such  matters  as  may  have  been  added 


FIG.  66. 


Diagram  of  the  alimentary  canal.    The  small  intestine  of  man  is  from  about  3  to  4 
times  as  long  as  the  large  intestine. 

to  it  in  its  passage,  is  discharged  from  the  rectum  through  the 
anus. 

We  shall  now  consider,  in  detail,  the  process  of  digestion,  as 
it  takes  place  in  each  stage  of  this  journey  of  the  food  through 
the  alimentary  canal. 


SALIVARY    GLANDS    AND    SALIVA.  209 

The  Salivary  Glands  and  the  Saliva. 

The  first  of  a  series  of  changes  to  which  the  food  is  subjected 
in  the  digestive  canal,  takes  place  in  the  cavity  of  the  mouth ; 
the  solid  articles  of  food  are  here  submitted  to  the  action  of 
the  teeth  (p.  51),  whereby  they  are  divided  and  crushed,  and 
by  being  at  the  same  time  mixed  with  the  fluids  of  the  mouth, 
are  reduced  to  a  soft  pulp,  capable  of  being  easily  swallowed. 
The  fluids  with  which  the  food  is  mixed  in  the  mouth  consist 
of  the  secretion  of  the  salivary  glands,  and  the  mucus  secreted 
by  the  lining  membrane  of  the  whole  buccal  cavity. 

The  glands  concerned  in  the  production  of  saliva,  are  very 
extensive,  and,  in  man  and  Mammalia  generally,  are  presented 
in  the  form  of  four  pairs  of  large  glands,  the  parotid,  submax- 
illary,  sublingual,  and  numerous  smaller  bodies,  of  similar 
structure  and  with  separate  ducts,  which  are  scattered  thickly 
beneath  the  mucous  membrane  of  the  lips,  cheeks,  soft  palate, 
and  root  of  the  tongue.  The  structure  of  all  these  glands  is 
essentially  the  same.  Each  is  composed  of  several  parts,  called 
lobes,  which  are  joined  together  by  areolar  tissue ;  and  each  of 
these  lobes,  again,  is  made  up  of  a  number  of  smaller  parts 
called  lobules,  bound  together  as  before  by  areolar  tissue.  Each 
of  these  small  divisions,  called  lobules,  is  a  miniature  represen- 
tation of  the  whole  gland.  It  contains  a  small  branch  of  the 
duct,  which,  subdividing,  ends  in  small  vesicular  pouches, 
called  acini,  a  group  of  which  may  be  considered  the  dilated 
end  of  one  of  the  smaller  ducts  (Fig.  67).  Each  of  the  acini 


Diagram  of  a  racemose  or  saccular  compound  gland  :  TO,  entire  gland,  showing 
branched  duct  and  lobular  structure  ;  n,  a  lobule  detached,  with  o,  branch  of  duct 
proceeding  from  it  (after  8harpey). 

is  about  ^j  of  an  inch  in  diameter,  and  is  formed  of  a  fine 
structureless  membrane,  lined  on  the  inner  surface  and  often 
filled  by  spheroidal  or  glandular  epithelium ;  while  on  the  out- 
side there  is  a  plexus  of  capillary  bloodvessels.  The  accom- 
panying diagram  is  intended  to  show  the  typical  structure  of 
such  glands  as  the  salivary  (Fig.  67). 


210 


DIGESTION. 


Saliva,  as  it  commonly  flows  from  the  mouth,  is  mixed  with 
the  secretion  of  the  mucous  membrane,  and  often  with  air- 
bubbles,  which,  being  retained  by  its  viscidity,  make  it  frothy. 

When  obtained  from  the  parotid  ducts,  and  free  from  mucus, 
saliva  is  a  transparent  watery  fluid,  the  specific  gravity  of 
which  varies  from  1.004  to  1.008,  and  in  which,  when  examined 
with  the  microscope,  are  found  floating  a  number  of  minute 
particles,  derived  from  the  secreting  ducts  and  vesicles  of  the 
glands.  In  the  impure  or  mixed  saliva  are  found,  besides 
these  particles,  numerous  epithelial  scales  separated  from  the 
surface  of  the  mucous  membrane  of  the  mouth  and  tongue, 
and  mucus-corpuscles,  discharged  for  the  most  part  from 
the  tonsils,  which,  when  the  saliva  is  collected  in  a  deep 
vessel,  and  left  at  rest,  subside  in  the  form  of  a  white  opaque 
matter,  leaving  the  supernatant  salivary  fluid  transparent  and 
colorless,  or  with  a  pale  bluish-gray  tint.  In  reaction,  the 
saliva,  when  first  secreted,  appears  to  be  always  alkaline ;  and 
that  from  the  parotid  gland  is  said  to  be  more  strongly  alka- 
line than  that  from  the  other  salivary  glands.  This  alkaline 
condition  is  most  evident  when  digestion  is  going  on,  and  ac- 
cording to  Dr.  Wright,  the  degree  of  alkalinity  of  the  saliva 
bears  a  direct  proportion  to  the  acidity  of  the  gastric  fluid  se- 
creted at  the  same  time.  During  fasting,  the  saliva,  although 
secreted  alkaline,  shortly  becomes  neutral ,  and  it  does  so  es- 
pecially when  secreted  slowly  and  allowed  to  mix  with  the 
acid  mucus  of  the  mouth,  by  which  its  alkaline  reaction  is 
neutralized. 

The  following  analysis  of  the  saliva  is  by  Frerichs : 


Composition  of  Saliva. 


Water, 
Solids, 


Ptyalin,      . 

Fat,    .... 

Epithelium  and  Mucus, 
Salts : 

Sulphocyanide  of  Potassium, 
Phosphate  of  Soda, 
"  Lime, 

"  Magnesia, 

Chloride  of  Sodium, 
u  Potassium, 


994.10 
5.90 

1.41 
0.07 
2.13 


2.29 


5.90 


The  rate  at  which  saliva  is  secreted  is  subject  to  considerable 
variation.     When  the  tongue  and  muscles  concerned  in  mas- 


USES    OF    SALIVA.  211 

tication  are  at  rest,  and  the  nerves  of  the  mouth  are  subject  to 
no  unusual  stimulus,  the  quantity  secreted  is  not  more  than 
sufficient,  with  the  mucus,  to  keep  the  mouth  moist.  But  the 
flow  is  much  accelerated  when  the  movements  of  mastication 
take  place,  and  especially  when  they  are  combined  with  the 
presence  of  food  in  the  mouth.  It  may  be  excited  also,  even 
when  the  mouth  is  at  rest,  by  the  mental  impressions  produced 
by  the  sight  or  thought  of  food  ;  also  by  the  introduction  of 
food  into  the  stomach.  The  influence  of  the  latter  circum- 
stance was  well  shown  in  a  case  mentioned  by  Dr.  Gairdner, 
of  a  man  whose  pharynx  had  been  divided  :  the  injection  of  a 
meal  of  broth  into  the  stomach  was  followed  by  the  secretion 
of  from  six  to  eight  ounces  of  saliva. 

Under  these  varying  circumstances,  the  quantity  of  saliva 
secreted  in  twenty-four  hours  varies  also ;  its  average  amount 
is  probably  from  two  to  three  pints  in  twenty-four  hours.  In 
a  man  who  had  a  fistulous  opening  of  the  parotid  duct,  Mits- 
cherlich  found  that  the  quantity  of  saliva  discharged  from  it 
during  twenty-four  hours,  was  from  two  to  three  ounces ;  and 
the  saliva  collected  from  the  mouth  during  the  same  period, 
and  derived  from  the  other  salivary  glands,  amounted  to  six 
times  more  than  that  from  the  one  parotid. 

The  purposes  served  by  saliva  are  of  several  kinds.  In  the 
first  place,  acting  mechanically  in  conjunction  with  mucus,  it 
keeps  the  mouth  in  a  due  condition  of  moisture,  facilitating 
the  movements  of  the  tongue  in  speaking,  and  the  mastication 
of  food.  (2.)  It  serves  also  in  dissolving  sapid  substances,  and 
rendering  them  capable  of  exciting  the  nerves  of  taste.  But 
the  principal  mechanical  purpose  of  the  saliva  is  (3)  that  by 
mixing  with  the  food  during  mastication,  it  makes  it  a  soft 
pulpy  mass,  such  as  may  be  easily  swallowed.  To  this  purpose 
the  saliva  is  adapted  both  by  quantity  and  quality.  For, 
speaking  generally,  the  quantity  secreted  during  feeding  is  in 
direct  proportion  to  the  dryness  and  hardness  of  the  food :  as 
M.  Lassaigne  has  shown,  by  a  table  of  the  quantity  produced 
in  the  mastication  of  a  hundred  parts  of  each  of  several  kinds 
of  food,  thirty  parts  suffice  for  a  hundred  parts  of  crumb  of 
bread,  but  not  less  than  120  for  the  crusts ;  42.5  parts  of  saliva 
are  produced  for  the  hundred  of  roast  meat;  3.7  for  as  much 
of  apples ;  and  so  on,  according  to  the  general  rule  above  stated. 
The  quality  of  saliva  is  equally  adapted  to  this  end.  It  is  easy 
to  see  how  much  more  readily  it  mixes  with  most  kinds  of  food 
than  water  alone  does ;  and  M.  Bernard  has  shown  that  the 
saliva  from  the  parotid,  labial,  and  other  small  glands,  being 
more  aqueous  than  the  rest,  is  that  which  is  chiefly  braided 
and  mixed  with  the  food  in  mastication;  while  the  more  viscid 


212  DIGESTION. 

mucoid  secretion  of  the  snbmaxillary,  palatine,  and  toiisillitic 
glands  is  spread  over  the  surface  of  the  softened  mass,  to  enable 
it  to  slide  more  easily  through  the  fauces  and  oesophagus. 
This  view  obtains  confirmation  from  the  interesting  fact  pointed 
out  by  Professor  Owen,  that  in  the  great  ant-eater,  whose  enor- 
mously elongated  tongue  is  kept  moist  by  a  large  quantity  of 
viscid  saliva,  the  submaxillary  glands  are  remarkably  devel- 
oped, while  the  parotids  are  not  of  unusual  size. 

Beyond  these,  its  mechanical  purposes,  saliva  performs  (4) 
a  chemical  part  in  the  digestion  of  the  food.  When  saliva,  or 
a  portion  of  a  salivary  gland,  or  even  a  portion  of  dried  ptyalin, 
is  added  to  starch  paste,  the  starch  is  very  rapidly  transformed 
into  dextrin  and  grape-sugar;  and  when  common  raw  starch 
is  masticated  and  mingled  with  saliva,  and  kept  with  it  at  a 
temperature  of  90°  or  100°,  the  starch  grains  are  cracked  or 
eroded,  and  their  contents  are  transformed  in  the  same  manner 
as  the  starch  paste.  Changes  similar  to  these  are  effected  on 
the  starch  of  farinaceous  food  (especially  after  cooking)  in  the 
stomach ;  and  it  is  reasonable  to  refer  them  to  the  action  of 
the  saliva,  because  the  acid  of  the  gastic  fluid  tends  to  retard 
or  prevent,  rather  than  favor  the  transformation  of  the  starch. 
It  may  therefore  be  held,  that  one  purpose  served  by  the  saliva 
in  the  digestive  process  is  that  of  assisting  in  the  transforma- 
tion of  the  starch  which  enters  so  largely  into  the  composition 
of  most  articles  of  vegetable  food,  and  which  (being  naturally 
insoluble)  is  converted  into  soluble  dextrin  and  grape-sugar, 
and  made  fit  for  absorption. 

Besides  saliva,  many  azotized  substances,  especially  if  in  a 
state  of  incipient  decomposition,  may  excite  the  transformation 
of  starch,  such  as  pieces  of  the  mucous  membrane  of  the  mouth, 
bladder,  rectum,  and  other  parts,  various  animal  and  vegetable 
tissues,  and  even  morbid  products;  but  the  gastric  fluid  will 
not  produce  the  same  effect.  The  transformation  in  question 
is  effected  much  more  rapidly  by  saliva,  however,  than  by  any 
of  the  other  fluids  or  substances  experimented  with,  except  the 
pancreatic  secretion,  which,  as  will  be  presently  shown,  is  very 
analogous  to  saliva.  The  actual  process  by  which  these  changes 
are  effected  is  still  obscure.  Probably  the  azotized  substance, 
ptyalin,  acts  as  a  kind  of  ferment,  like  diastase  in  the  process 
of  malting,  and  excites  molecular  changes  in  the  starch  which 
result  in  its  transformation,  first  into  dextrin  and  then  into 
sugar. 

The  majority  of  observers  agree  that  the  transformation  of 
starch  into  sugar  ceases  on  the  entrance  of  the  food  into  the 
stomach,  or  on  the  addition  of  gastric  fluid  to  it  in  a  test-tube  : 
while  others  maintain  that  it  still  goes  on.  Probably  all  are 


DEGLUTITION.  213 

right:  for,  although  gastric  fluid  added  to  saliva  appears  to 
arrest  the  action  of  the  latter  on  starch,  yet  portions  of  saliva 
mingled  with  food  in  mastication  may,  for  some  time  after  their 
entrance  into  the  stomach,  remain  unneutralized  by  the  gastric 
secretion,  and  continue  their  influence  upon  the  starchy  prin- 
ciples in  contact  with  them. 

Starch  appears  to  be  the  only  principle  of  food  upon  which 
saliva  acts  chemically :  it  has  no  apparent  influence  on  any  of 
the  other  ternary  principles,  such  as  sugar,  gum,  cellulose,  or 
(according  to  Bernard)  on  fat,  and  seems  to  be  equally  desti- 
tute of  power  over  albuminous  and  gelatinous  substances,  so 
that  we  have  as  yet  no  information  respecting  any  purpose  it 
can  serve  in  the  digestion  of  Carnivora,  beyond  that  of  soften- 
ing or  macerating  the  food;  though,  since  such  animals  masti- 
cate their  food  very  little,  usually  "  bolting  "  it,  the  saliva  has 
probably  but  little  use  even  in  this  respect,  in  the  process  of 
digestion. 

Passage  of  Food  into  the  Stomach. 

When  properly  masticated,  the  food  is  transmitted  in  suc- 
cessive portions  to  the  stomach  by  the  act  of  deglutition  or 
swallowing.  This  act,  for  the  purpose  of  description,  may  be 
divided  into  three  parts.  In  the  first,  particles  of  food  col- 
lected to  a  morsel  glide  between  the  surface  of  the  tongue  and 
the  palatine  arch,  till  they  have  passed  the  anterior  arch  of 
the  fauces ;  in  the  second,  the  morsel  is  carried  through  the 
pharynx  ;  and  in  the  third,  it  reaches  the  stomach  through  the 
O3sophagus.  These  three  acts  follow  each  other  rapidly.  The 
first  is  performed  voluntarily  by  the  muscles  of  the  tongue  and 
cheeks.  The  second  also  is  effected  with  the  aid  of  muscles 
which  are  in  part  endued  with  voluntary  motion,  such  as  the 
muscles  of  the  soft  palate  and  pharynx  ;  but  it  is,  nevertheless, 
an  involuntary  act,  and  takes  place  without  our  being  able  to 
prevent  it,  as  soon  as  a  morsel  of  food,  drink,  or  saliva  is 
carried  backwards  to  a  certain  point  of  the  tongue's  surface. 
When  we  appear  to  swallow  voluntarily,  we  only  convey, 
through  the  first  act  of  deglutition,  a  portion  of  food  or  saliva 
beyond  the  anterior  arch  of  the  palate ;  then  the  substance  acts 
as  a  stimulus,  which,  in  accordance  with  the  laws  of  reflex 
movements  hereafter  to  be  described,  is  carried  by  the  sensi- 
tive nerves  to  the  medulla  oblongata,  when  it  is  reflected  by 
the  motor  nerves,  and  an  involuntary  adapted  action  of  the 
muscles  of  the  palate  and  pharynx  ensues.  The  third  act  of 
deglutition  takes  place  in  the  oesophagus,  the  muscular  fibres 
of  which  are  entirely  beyond  the  influence  of  tlje  will. 

The  second  act  of  deglutition  is  the  most  complicated,  be- 


214  DIGESTION. 

cause  the  food  must  pass  by  the  posterior  orifice  of  the  nose 
and  the  upper  opening  of  the  larynx  without  touching  them. 
When  it  has  been  brought,  by  the  first  act,  between  the  an- 
terior arches  of  the  palate,  it  is  moved  onwards  by  the  tongue 
being  carried  backwards,  and  by  the  muscles  of  the  anterior 
arches«contracting  on  it  and  then  behind  it.  The  root  of  the 
tongue  being  retracted,  and  the  larynx  being  raised  with  the 
pharynx  and  carried  forwards  under  the  tongue,  the  epiglottis 
is  pressed  over  the  upper  opening  of  the  larynx,  and  the  mor- 
sel glides  past  it ;  the  closure  of  the  glottis  being  additionally 
secured  by  the  simultaneous  contraction  of  its  own  muscles  :  so 
that,  even  when  the  epiglottis  is  destroyed,  there  is  little  danger 
of  food  or  drink  passing  into  the  larynx  so  long  as  its  muscles 
can  act  freely.  At  the  same  time  the  raising  of  the  soft  palate, 
so  that  its  posterior  edge  touches  the  back  part  of  the  pharynx, 
and  the  approximation  of  the  sides  of  the  posterior  palatine 
arch,  which  move  quickly  inwards  like  side  curtains,  close  the 
passage  into  the  upper  part  of  the  pharynx  and  the  posterior 
nares,  and  form  an  inclined  plane,  along  the  under  surface  of 
which  the  morsel  descends;  then  the  pharynx,  raised  up  to 
receive  it,  in  its  turn  contracts,  and  forces  it  onwards  into  the 
oesophagus. 

In  the  third  act,  in  which  the  food  passes  through  the  oesoph- 
agus, every  part  of  that  tube  as  it  receives  the  morsel  and 
is  dilated  by  it,  is  stimulated  to  contract :  hence  an  undulatory 
contraction  of  the  oesophagus,  which  is  easily  observable  in 
horses  while  drinking,  proceeds  rapidly  along  the  tube.  It  is 
only  when  the  morsels  swallowed  are  large,  or  taken  too  quickly 
in  succession,  that  the  progressive  contraction  of  the  oesophagus 
is  slow,  and  attended  with  pain.  Division  of  both  pneumo- 
gastric  nerves  paralyzes  the  contractile  power  of  the  oesophagus, 
and  food  accordingly  accumulates  in  the  tube  (Bernard). 

DIGESTION    OF    FOOD    IN   THE   STOMACH. 

Structure  of  the  Stomach. 

It  appears  to  be  an  almost  universal  character  of  animals, 
that  they  have  ^n  internal  cavity  for  the  production  of  a 
chemical*  change  in  the  aliment — a  cavity  for  digestion  ;  and 
when  this  cayity  is  compound,  th'e  part  in  which  the  food 
undergoes  its  principal  and  most  important  changes  is  the 
stomach. 

In  man  and  those  Mammalia  which  are  provided  with  a 
single  stomach,  its  walls  consist  of  three  distinct  layers  or  coats, 
viz.,  an  external  peritoneal,  an  internal  mucous,  and  an  inter- 


STRUCTURE    OF     THE    STOMACH.  215 

mediate  muscular  coat,   with    bloodvessels,   lymphatics,  and 
nerves  distributed  in  and  between  them. 

The  muscular  coat  of  the  stomach  consists  of  three  separate 
layers  or  sets  of  fibres,  which,  according  to  their  several  direc- 
tions, are  named  the  longitudinal,  circular,  and  oblique.  The 
longitudinal  set  are  the  most  superficial :  they  are  continuous 
with  the  longitudinal  fibres  of  the  oesophagus,  and  spread  out 
in  a  diverging  manner  over  the  great  end  and  sides  of  the 
stomach.  They  extend  as  far  as  the  pylorus,  being  especially 
distinct  at  the  lesser  or  upper  curvature  of  the  stomach,  along 
which  they  pass  in  several  strong  bands.  The  next  set  are  the 
circular  or  transverse  fibres,  which  more  or  less  completely  en- 
circle all  parts  of  the  stomach  ;  they  are  most  abundant  at  the 
middle  and  in  the  pyloric  portion  of  the  organ,  and  form  the 
chief  part  of  the  thick  projecting  ring  of  the  pylorus.  Accord- 
ing to  Pettigrew,  these  fibres  are  not  simple  circles,  but  form 
double  or  figure-of-8  loops,  the  fibres  intersecting  very  obliquely. 
The  next,  and  consequently  deepest  set  of  fibres,  are  the  oblique, 
continuous  with  the  circular  muscular  fibres  of  the  oesophagus, 
and  according  to  Pettigrew,  with  the  same  double-looped  ar- 
rangement that  prevails  in  the  preceding  layer:  they  are  com- 
paratively few  in  number,  and  are  placed  only  at  the  cardiac 
orifice  and  portion  of  the  stomach,  over  both  surfaces  of  which 
they  are  spread,  some  passing  obliquely  from  left  to  right, 
others  from  right  to  left,  around  the  cardiac  orifice,  to  which, 
by  their  interlacing,  they  form  a  kind  of  sphincter,  continu- 
ous with  that  around  the  lower  end  of  the  oesophagus.  The 
fibres  of  which  the  several  muscular  layers  of  the  stomach,  and 
of  the  intestinal  canal  generally,  are  composed,  belong  to  the 
class  of  organic  muscle,  being  composed  of  smooth  or  unstriped, 
elongated,  spindle-shaped  fibre-cells ;  a  fuller  description  of 
which  will  be  given  under  the  head  of  Muscular  Tissue. 

The  mucous  membrane  of  the  stomach,  which  rests  upon  a 
layer  of  loose  cellular  membrane,  or  submucous  tissue,  is 
smooth,  level,  soft,  and  velvety ;  of  a  pale  pink  color  during 
life,  and  in  the  contracted  state  is  thrown  into  numerous,  chiefly 
longitudinal,  folds  or  rugae,  which  disappear  when  the  organ 
is  distended. 

In  its  general  structure  the  mucous  membrane  of  the  stomach 
resembles  that  of  other  parts.  (See  Structure  of  Mucous 
Membrane.)  But  there  are  certain  peculiarities  shared  with 
the  mucous  membrane  of  the  small  and  large  intestines,  which, 
doubtless,  are  connected  with  the  peculiar  functions,  especially 
those  relating  to  absorption,  which  these  parts  of  the  alimen- 
tary canal  perform. 

Entering  largely  into  the  construction  of  the  mucous  mem- 


216  DIGESTION. 

brane,  especially  in  the  superficial  part  of  the  corium,  is  a 
quantity  of  a  very  delicate  kind  of  connective  tissue,  called 
retiform  tissue  (Fig.  72),  or  sometimes  lymphoidor  adenoid  tis- 
sue, because  it  so  closely  resembles  that  which  forms  the  stroma, 
or  supporting  framework  of  lymphatic  glands  (see  section  on 
Lymphatic  Glands);  the  resemblance  being  made  much  closer 
by  the  fact  that  the  interspaces  of  this  retiform  tissue  are  filled 
with  corpuscles  not  to  be  distinguished  from  lymph-corpuscles. 

At  the  deepest  part  of  the  mucous  membrane,  is  a  layer  of 
unstriped  muscular  fibres,  called  the  muscularis  mucosce,  which 
must  not  be  confounded  with  the  layers  of  muscle  constituting 
the  proper  muscular  coat,  and  from  which  it  is  separated  by 
the  submucous  tissue.  The  muscularis  mucosce  is  found  in  the 
oesophagus,  as  well  as  in  the  stomach  and  intestines. 

When  examined  with  a  lens,  the  internal  or  free  surface  of 
the  stomach  presents  a  peculiar  honeycomb  appearance,  pro- 
duced by  shallow  polygonal  depressions  or  cells  (Fig.  68),  the 
diameter  of  which  varies  generally  from  ^Oth  to  3^Dth  of  an 
inch  ;  but  near  the  pylorus  is  as  much  as  yj$th  of  an  inch. 
They  are  separated  by  slightly  elevated  ridges,  which  some- 
times, especially  in  certain  morbid  states  of  the  stomach,  bear 
minute,  narrow,  vascular  processes,  which  look  like  villi,  and 
have  given  rise  to  the  erroneous  supposition  that  the  stomach 
has  absorbing  villi,  like  those  of  the  small  intestines.  lu  the 
bottom  of  the  cells  minute  openings  are  visible  (Fig.  68),  which 

FIG.  68. 


Small  portion  of  the  surface  of  the  mucous  membrane  of  the  stomach  (from 
Ecker)  30_  The  specimen  shows  the  shallow  depressions,  in  each  of  which  the 
smaller  dark  spots  indicate  the  orifices  of  a  variable  number  of  the  gastric  tubular 
glands. 

are  the  orifices  of  perpendicularly  arranged  tubular  glands 
(Fig.  69),  imbedded  side  by  side  in  sets  or  bundles,  in  the  sub- 
stance of  the  mucous  membrane,  and  composing  nearly  the 
whole  structure. 

The  glands  which  are  found  in  the  human  stomach  may  be 
divided  into  two  classes,  the  tubular  and  lenticular. 

Tubular  glands. — The  tubular  glands  may  be  described  as  a 
collection  of  cylinders  with  blind  extremities,  about  r^th  of  an 


GLANDS    OF    THE    STOMACH.  217 

FIG.  69. 

Surface  of  mucous  membrane. 

Gastric  tubes. 

Dense  areolar  tissue. 

Submucous    tissue    of  looser 
texture. 

Transverse  muscular  fibres. 

Longitudinal  muscular  fibres. 
Peritoneum. 

Portion  of  human  stomach  (magnified  30  diameters)  cut  vertically,  both  in  a  direc- 
tion parallel  to  its  long  axis,  and  across  it  (altered  from  Brinton). 


The  gastric  glands  of  the  human  stomach  (magnified),  a,  deep  part  of  a  pyloric 
gastric  gland  (from  Kolliker) ;  the  cylindrical  epithelium  is  traceable  to  the  csecal 
extremities,  b  and  c,  cardiac  gastric  glands  (from  Allen  Thompson) ;  b,  vertical  sec- 
tion of  a  small  portion  of  the  mucous  membrane  with  the  glands  magnified  30  diame- 
ters ;  c,  deeper  portion  of  one  of  the  glands,  magnified  65  diameters,  showing  a  slight 
division  of  the  tubes,  and  a  sacculated  appearance,  produced  by  the  large  glandular 
cells  within  them  ;  d,  cellular  elements  of  the  cardiac  glands  magnified  250  diameters. 


218 


DIGESTION. 


FIG.  71. 


inch  in  length,  and  ^Oth  in  diameter,  packed  closely  together, 
with  their  long  axis  at  right  angles  to  the  surface  of  the 
mucous  membrane  on  which  they  open,  their  blind  ends  rest- 
ing on  the  subrnucous  tissue.  (See  Fig.  69.)  They  are  all 
composed  of  basement-membrane,  and  lined  by  epithelial  cells, 
but  they  are  not  all  of  exactly  similar  shape ;  for  while  some 
are  simple  straight  tubes,  open  at  one  end  and  closed  at  the 
other  (Fig.  69),  others  present  at  their  deeper  extremities 
a  varicose,  pouched,  or  in  some  cases,  even  a  branched  ap- 
pearance (Fig.  70,  b  and  c).  The  epithelium  lining  them  is 
not  the  same  throughout.  In  the  upper  third  or  fourth  of  their 
length  it  is  cylindrical,  and  continuous  with  that  which  covers 
the  free  mucous  surface  of  the  rest  of  the  stomach.  In  their 
lower  part,  on  the  other  hand,  it  is  of  the  variety  called  glan- 
dular or  spheroidal,  the  cells  being  oval  or  somewhat  angular, 
and  about  j^^th  of  an  inch  in  diameter.  The  cells,  however 
do  not  completely  fill  up  the  cavity  of  the  gland  wrhich  they 

line,  but  leave  a  slight,  central, 
thread-like  space,  the  immediate 
lining  of  which  is  a  layer  of 
small  angular  cells,  continuous 
with  the  cylindrical  epithelium 
in  the  upper  portion  of  the  tube. 
This  description  will  become 
plain  on  reference  to  Fig.  71, 
which  represents  on  a  larger 
scale  a  longitudinal  section  of 
one  of  the  glands  depicted  in 
Fig.  69.  In  the  greater  number 
of  the  glands  which  are  branched 
at  their  deeper  extremities,  the 
spheroidal  epithelium  exists  in 
the  divisions,  while  the  main 
duct  and  the  upper  part  of  the 
branches  are  lined  by  the  cylin- 
drical variety  (Fig.  70,  c).  In 
the  human  stomach,  according 
to  Dr.  Brinton,  the  simple  un- 
divided tubes  are  the  rule,  and 
the  branched  the  exception. 

The  varieties  in  the  epithelial 
cells  lining  the  different  parts  of 
the  tubes,  correspond  probably 
with  differences  in  the  fluid  se- 
creted by  their  agency — the  cyl- 
inder-epithelium, like  that  on  the  free  surface  of  the  stomach, 


Part  of  one  of  the  gastric  glands 
highly  magnified,  to  show  the  ar- 
rangement of  the  epithelium  in  its 
interior ;  a,  columnar  cells  lining  the 
upper  part  of  the  tube ;  b,  small  an- 
gular cells,  into  which  these  merge 
below  to  form  a  central  or  axial 
layer  within ;  c,  the  proper  gastric 
or  glandular  cells  (after  Brinton). 


THE    GASTRIC     FLUID.  219 

being  probably  engaged  in  separating  the  thin  alkaline  mucus, 
which  is  always  present  in  greater  or  less  quantity,  while  the 
larger  glandular  cells  probably  secrete  the  proper  gastric  juice. 

Near  the  pylorus  there  exist  glands  branched  at  their  deep 
extremities,  which  are  lined  throughout  by  cylinder-epithelium 
(Fig.  70,  a),  and  probably  serve  only  for  the  secretion  of 
mucus. 

All  the  tubular  glands,  while  they  open  by  one  end  into  the 
cavity  of  the  stomach,  rest  by  their  blind  extremities  on  a  bed 
or  matrix  of  areolar  tissue  (Fig.  69),  which  is  prolonged  up- 
wards between  them,  so  as  to  invest  and  support  them. 

Lenticular  Glands. — Besides  the  cylindrical  glands,  there 
are  also  small  closed  sacs  beneath  the  surface  of  the  mucous 
membrane,  resembling  exactly  the  solitary  glands  of  the  intes- 
tine, to  be  described  hereafter.  Their  number  is  very  variable, 
and  they  are  found  chiefly  along  the  lesser  curvature  of  the 
stomach,  and  in  the  pyloric  region,  but  they  may  be  present 
in  any  part  of  the  organ.  According  to  Dr.  Brinton  they  are 
rarely  absent  in  children.  Their  function  probably  resembles 
that  of  the  intestinal  solitary  glands,  but  nothing  is  certainly 
known  regarding  it. 

The  bloodvessels  of  the  stomach,  which  first  break  up  in  the 
submucous  tissue,  send  branches  upward  between  the  closely 
packed  glandular  tubes,  anastomosing  around  them  by  means 
of  a  fine  capillary  network  with  oblong  meshes.  Continuous 
with  this  deeper  plexus,  or  prolonged  upwards  from  it,  so  to 
speak,  is  a  more  superficial  network  of  larger  capillaries,  which 
branch  densely  around  the  orifices  of  the  tubes,  and  form  the 
framework  on  which  are  moulded  the  small  elevated  ridges  of 
mucous  membrane  bounding  the  minute,  polygonal  pits  before 
referred  to.  From  this  superficial  network  the  veins  chiefly 
take  their  origin.  Thence  passing  down  between  the  tubes, 
with  no  very  free  connection  with  the  deeper  intertubular  capil- 
lary plexus,  they  open  finally  into  the  venous  network  in  the 
submucous  tissue. 

The  nerves  of  the  stomach  are  derived  from  the  pneumo- 
gastric  and  sympathetic. 

Secretion  and  Properties  of  the  Gastric  Fluid. 

While  the  stomach  contains  no  food,  and  is  inactive,  no 
gastric  fluid  is  secreted;  and  mucus,  which  is  either  neutral  or 
slightly  alkaline,  covers  its  surface.  But  immediately  on  the 
introduction  of  food  or  other  foreign  substance  into  the  stom- 
ach, the  mucous  membrane,  previously  quite  pale,  becomes 
slightly  turgid  and  reddened  with  the  influx  of  a  larger  quan- 


220  DIGESTION. 

tity  of  blood;  the  gastric  glands  commence  secreting  actively, 
and  an  acid  fluid  is  poured  out  in  minute  drops,  which  gradu- 
ally run  together  and  flow  down  the  walls  of  the  stomach,  or 
soak  into  the  substances  introduced.  The  quantity  of  this  fluid 
secreted  daily  has  been  variously  estimated ;  but  the  average 
for  a  healthy  adult  has  been  assumed  to  range  from  ten  to 
twenty  pints  in  the  twenty-four  hours  (Brinton). 

The  first  accurate  analysis  of  the  gastric  fluid  was  made  by 
Dr.  Prout;  but  it  does  not  appear  that  it  was  collected  in  any 
large  quantity,  or  pure  and  separate  from  food,  until  the  time 
when  Dr.  Beaumont  was  enabled,  by  a  fortunate  circumstance, 
to  obtain  it  from  the  stomach  of  a  man  named  St.  Martin,  in 
whom  there  existed,  as  the  result  of  a  gunshot  wound,  an  open- 
ing leading  directly  into  the  stomach,  near  the  upper  extremity 
of  the  great  curvature,  and  three  inches  from  the  cardiac  orifice. 
The  external  opening  was  situate  two  inches  below  the  left 
mamma,  in  a  line  drawn  from  that  part  to  the  spine  of  the 
left  ilium.  The  borders  of  the  opening  into  the  stomach,  which 
was  of  considerable  size,  had  united,  in  healing,  with  the  mar- 
gins of  the  external  wound,  but  the  cavity  of  the  stomach  was 
at  last  separated  from  the  exterior  by  a  fold  of  mucous  mem- 
brane, which  projected  from  the  upper  and  back  part  of  the 
opening,  and  closed  it  like  a  valve,  but  could  be  pushed  back 
with  the  finger.  The  introduction  of  any  mechanical  irritant, 
such  as  the  bulb  of  a  thermometer,  into  the  stomach,  excited 
at  once  the  secretion  of  gastric  fluid.  This  could  be  drawn  off 
with  a  caoutchouc  tube,  and  could  often  be  obtained  to  the 
extent  of  nearly  an  ounce.  The  introduction  of  alimentary 
substances  caused  a  much  more  rapid  and  abundant  secretion 
of  pure  gastric  fluid  than  the  presence  of  other  mechanical 
irritants  did.  No  increase  of  temperature  could  be  detected 
during  the  most  active  secretion ;  the  thermometer  introduced 
into  the  stomach  always  stood  at  100°  Fahr.,  except  during 
muscular  exertion,  when  the  temperature  of  the  stomach,  like 
that  of  other  parts  of  the  body,  rose  one  or  two  degrees  higher. 

M.  Blondlot,  and  subsequently  M.  Bernard,  and  since  then, 
several  others,  by  maintaining  fistulous  openings  into  the 
stomachs  of  dogs,  have  confirmed  most  of  the  facts  discovered 
by  Dr.  Beaumont.  And  the  man  St.  Martin  has  frequently 
submitted  to  renewed  experiments  on  his  stomach,  by  various 
physiologists.  From  all  these  observations  it  appears,  that 
pepper,  salt,  and  other  soluble  stimulants,  excite  a  more  rapid 
discharge  of  gastric  fluid  than  mechanical  irritation  does ;  so 
do  alkalies  generally,  but  acids  have  a  contrary  effect.  When 
mechanical  irritation  is  carried  beyond  certain  limits  so  as  to 
produce  pain,  the  secretion,  instead  of  being  more  abundant, 


THE    GASTRIC     FLUID.  221 

diminishes  or  ceases  entirely,  and  a  ropy  mucus  is  poured  out 
instead.  Very  cold  water,  or  small  pieces  of  ice,  at  first  ren- 
der the  mucous  membrane  pallid,  but  soon  a  kind  of  reaction 
ensues,  the  membrane  becomes  turgid  with  blood,  and  a  larger 
quantity  of  gastric  juice  is  poured  out.  The  application  of  too 
much  ice  is  attended  by  diminution  in  the  quantity  of  fluid 
secreted,  and  by  consequent  retardation  of  the  process  of  di- 
gestion. The  quantity  of  the  secretion  seems  to  be  influenced 
also  by  impressions  made  on  the  mouth  ;  for  Blondlot  found 
that  when  sugar  was  introduced  into  the  dog's  stomach,  either 
alone,  or  mixed  with  human  saliva,  a  very  small  secretion  en- 
sued :  but  when  the  dog  had  himself  masticated  and  swallowed 
it,  the  secretion  was  abundant. 

Dr.  Beaumont  described  the  secretion  of  the  human  stomach 
as  "  a  clear  transparent  fluid,  inodorous,  a  little  saltish,  and 
very  perceptibly  acid.  Its  taste  is  similar  to  that  of  thin  mu- 
cilaginous water,  slightly  acidulated  with  muriatic  acid.  It 
is  readily  diffusible  in  water,  wine,  or  spirits ;  slightly  effer- 
vesces with  alkalies ;  and  is  an  effectual  solvent  of  the  materia 
alimentaria.  It  possesses  the  property  of  coagulating  albumen 
in  an  eminent  degree ;  is  powerfully  antiseptic,  checking  the 
putrefaction  of  meat ;  and  effectually  restorative  of  healthy 
action,  when  applied  to  old  fetid  sores  and  foul  ulcerating 
surfaces." 

The  chemical  composition  of  the  gastric  juice  of  the  human 
subject  has  been  particularly  investigated  by  Schmidt,  a  favor- 
able case  for  his  doing  so  occurring  in  the  person  of  a  peasant 
named  Catharine  Kiitt,  aged  35,  who  for  three  years  had  had 
a  gastric  fistula  under  the  left  mammary  gland,  between  the 
cartilages  of  the  ninth  and  tenth  ribs. 

The  fluid  was  obtained  by  putting  into  the  stomach  some 
hard  indigestible  matter,  as  dry  peas,  and  a  little  water,  by 
which  means  the  stomach  was  excited  to  secretion,  at  the  same 
time  that  the  matter  introduced  did  not  complicate  the  analy- 
sis by  being  digested  in  the  fluid  secreted.  The  gastric  juice 
was  drawn  off  through  an  elastic  tube  inserted  into  the  fistula. 

The  fluid  thus  obtained  was  acid,  limpid,  and  odorless, 
with  a  mawkish  taste.  Its  density  varied  from  1.0022  to  1.0024. 
Under  the  microscope  a  few  cells  from  the  gastric  glands  and 
some  fine  granular  matter  were  observable. 

The  following  table  gives  the  mean  of  two- analyses  of  the 
above-mentioned  fluid ;  and  arranged  by  the  side  of  it,  for 
purposes  of  comparison,  is  an  analysis  of  gastric  juice  from 
the  sheep  and  dog. 

19 


222  DIGESTION. 


Composition  of  Gastric  Juice. 

Human  Sheep's  Dog's 

Gastric  Juice.    Gastric  Juice.  Gastric  Juice. 

Water,          ....     994.40  986.14  971.17 

Solid  Constituents,       .         .         5.-r>9  13.85  2882 


Solids. 


f  Ferment,  Pepsin  (with 

a  trace  of  Ammonia),  3.19  4.20  17.50 

Hydrochloric  Acid,     .  0.20  1.55  2.70 

Chloride  of  Calcium,  .  0.06  0.1 1  1.66 

Sodium,    .  1.46  4.36  314 

"             Potassium,  0.55  1.51  1.07 
Phosphate     of     Lime, 

[       Magnesia,  and  Iron,  0.12  2.09  2.73 

Iii  all  the  above  analyses  the  amount  of  water  given  must 
be  reckoned  as  rather  too  much,  inasmuch  as  a  certain  quan- 
tity of  saliva  was  mixed  with  the  gastric  fluid.  The  allow- 
ance, however,  to  be  made  on  this  account  is  only  very  small. 

Considerable  difference  of  opinion  has  existed  concerning 
the  nature  of  the  free  acid  contained  in  the  gastric  juice, 
chiefly  whether  it  is  hydrochloric  or  lactic.  The  weight  of 
evidence,  however,  is  in  favor  of  free  hydrochloric  acid,  being 
that  to  which,  in  the  human  subject,  the  acidity  of  the  gastric 
fluid  is  mainly  due ;  although  there  is  no  doubt  that  others, 
as  lactic,  acetic,  butyric,  are  not  unfrequently  to  be  found 
therein. 

The  animal  matter  mentioned  in  the  analysis  of  the  gastric 
fluid  is  named  pepsin,  from  its  power  in  the  process  of  diges- 
tion. It  is  an  azotized  substance,  and  is  best  procured  by  di- 
gesting portions  of  the  mucous  membrane  of  the  stomach  in 
cold  water,  after  they  have  been  macerated  for  some  time  in 
water  at  a  temperature  between  80°  and  100°  F.  The  warm 
water  dissolves  various  substances  as  well  as  some  of  the  pepsin, 
but  the  cold  water  takes  up  little  else  than  pepsin,  which,  on 
evaporating  the  cold  solution,  is  obtained  in  a  grayish-brown 
viscid  fluid.  The  addition  of  alcohol  throws  down  the  pepsin 
in  grayish-white  flocculi ;  and  one  part  of  the  principle  thus 
prepared,  if  dissolved  in  even  60,000  parts  of  water,  will 
digest  meat  and  other  alimentary  substances. 

The  digestive  power  of  the  gastric  fluid  is  manifested  in  its 
softening,  reducing  into  pulp,  and  partially  or  completely  dis- 
solving various  articles  of  food  placed  in  it  at  a  temperature 
of  from  90°  to  100°.  This,  its  peculiar  property,  requires  the 
presence  of  both  the  pepsin  and  the  acid  ;  neither  of  them  can 
digest  alone,  and  when  they  are  mixed,  either  the  decomposi- 
tion of  the  pepsin,  or  the  neutralization  of  the  acid,  at  once 


DIGESTIVE    POWER    OF   GASTRIC    FLUID.       223 

destroys  the  digestive  property  of  the  fluid.  For  the  perfec- 
tion of  the  process  also,  certain  conditions  are  required,  which 
are  all  found  in  the  stomach ;  namely  (1),  a  temperature  of 
about  100°  F. ;  (2),  such  movements  as  the  food  is  subjected 
to  by  the  muscular  actions  of  the  stomach,  which  bring  in  suc- 
cession every  part  of  it  in  contact  with  the  mucous  membrane, 
whence  the  fresh  gastric  fluid  is  being  secreted ;  (3),  the  con- 
stant removal  of  those  portions  of  food  which  are  already 
digested,  so  that  what  remains  undigested  may  be  brought 
more  completely  into  contact  with  the  solvent  fluid ;  and  (4) 
a  state  of  softness  and  minute  division,  such  as  that  to  which 
the  food  is  reduced  by  mastication  previous  to  its  introduction 
into  the  stomach. 

The  chief  circumstances  connected  with  the  mode  in  which 
the  gastric  fluid  acts  upon  food  during  natural  digestion,  have 
been  determined  by  watching  its  operations  when  removed 
from  the  stomach  and  placed  in  conditions  as  nearly  as  possi- 
ble like  those  under  which  it  acts  while  within  that  viscus. 
The  fact  that  solid  food,  immersed  in  gastric  fluid  out  of  the 
body,  and  kept  at  a  temperature  of  about  100°,  is  gradually 
converted  into  a  thick  fluid  similar  to  chyme,  was  shown  by 
Spallanzani,  Dr.  Stevens,  Tiedemann  and  Gmelin  and  others. 
They  used  the  gastric  fluid  of  dogs,  obtained  by  causing  the 
animals  to  swallow  small  pieces  of  sponge,  which  were  subse- 
quently withdrawn,  soaked  with  the  fluid — and  proved  nearly 
as  much  as  the  latter  experiments  of  the  same  kind  of  gastric 
fluid  by  Blondlot,  Bernard  and  others.  But  these  need  not 
be  particularly  referred  to,  while  we  have  the  more  satisfac- 
tory and  instructive  observations  which  Dr.  Beaumont  made 
with  the  fluid  obtained  from  the  stomach  of  St.  Martin. 
After  the  man  had  fasted  seventeen  hours,  Dr.  Beaumont  took 
one  ounce  of  gastric  fluid,  put  into  it  a  solid  piece  of  boiled 
recently  salted  beef  weighing  three  drachms,  and  placed  the 
vessel  which  contained  them  in  a  water-bath  heated  to  100°. 
"  In  forty  minutes  digestion  had  distinctly  commenced  over 
the  surface  of  the  meat ;  in  fifty  minutes,  the  fluid  had  become 
quite  opaque  and  cloudy,  the  external  texture  began  to  separate 
and  become  loose  ;  and  in  sixty  minutes  chyme  began  to  form. 
At  1  P.M."  (two  hours  after  the  commencement  of  the  experi- 
ment) "  the  cellular  texture  seemed  to  be  entirely  destroyed, 
leaving  the  muscular  fibres  loose  and  unconnected,  floating 
about  in  small  fine  shreds,  very  tender  and  soft."  In  six  hours, 
they  were  nearly  all  digested — a  few  fibres  only  remaining. 
After  the  lapse  of  ten  hours,  every  part  of  the  meat  was  com- 
pletely digested.  The  gastric  juice,  which  was  at  first  trans-; 
parent,  was  now  about  the  color  of  whey,  and  deposited  a  fine 


224  DIGESTION. 

sediment  of  the  color  of  meat.  A  similar  piece  of  beef  was,  at 
the  time  of  the  commencement  of  this  experiment,  suspended 
in  the  stomach  by  means  of  a  thread  :  at  the  expiration  of  the 
first  hour  it  was  changed  in  about  the  same  degree  as  the  meat 
digested  artificially ;  but  at  the  end  of  the  second  hour,  it  was 
completely  digested  and  gone. 

In  other  experiments,  Dr.  Beaumont  withdrew  through  the 
opening  of  the  stomach  some  of  the  food  which  had  been  taken 
twenty  minutes  previously,  and  which  was  completely  mixed 
with  the  gastric  juice.  He  continued  the  digestion,  which  had 
already  commenced,  by  means  of  artificial  heat  in  a  water-bath. 
In  a  few  hours  the  food  thus  treated  was  completely  chymified  ; 
and  the  artificial  seemed  in  this,  as  in  several  other  experi- 
ments, to  be  exactly  similar  to,  though  a  little  slower  than,  the 
natural  digestion. 

The  apparent  identity  of  the  process  in-  and  outside  of  the 
stomach  thus  manifested,  while  it  shows  that  we  may  regard 
digestion  as  essentially  a  chemical  process,  when  once  the  gas- 
tric fluid  is  formed,  justifies  the  belief  that  Dr.  Beaumont's 
other  experiments  with  the  digestive  fluid  may  exactly  repre- 
sent the  modifications  to  which,  under  similar  conditions,  its 
action  in  the  stomach  would  be  liable.  He  found  that,  if  the 
mixture  of  food  and  gastric  fluid  were  exposed  to  a  temperature 
of  34°  F.,  the  process  of  digestion  was  completely  arrested.  In 
another  experiment,  a  piece  of  meat  which  had  been  macerated 
in  water  at  a  temperature  of  100°  for  several  days,  till  it  ac- 
quired a  strong  putrid  odor,  lost,  on  the  addition  of  some  fresh 
gastric  juice,  all  signs  of  putrefaction,  and  soon  began  to  be 
digested.  From  other  experiments  he  obtained  the  data  for 
estimates  of  the  degrees  of  digestibility  of  various  articles  of 
food,  and  of  the  ways  in  which  the  digestion  is  liable  to  be  af- 
fected, to  which  reference  will  again  be  made. 

When  natural  gastric  juice  cannot  be  obtained,  many  of 
these  experiments  may  be  performed  with  an  artificial  digestive 
fluid,  the  action  of  which,  probably,  very  closely  resembles  that 
of  the  fluid  secreted  by  the  stomach.  It  is  made  by  macerat- 
ing in  water  portions  of  fresh  or  recently  dried  mucous  mem- 
brane of  the  stomach  of  a  pig1  or  other  omnivorous  animal, 
or  of  the  fourth  stomach  of  the  calf,  and  adding  to  the  in- 
fusion a  few  drops  of  hydrochloric  acid — about  3.3  grains  to 
half  an  ounce  of  the  mixture,  according  to  Schwann.  Por- 
tions of  food  placed  in  such  fluid,  and  maintained  with  it 


1  The  best  portion  of  the  stomach  of  the  pig  for  this  purpose  is  that 
between  the  cardiac  and  pyloric  orifices ;  the  cardiac  portion  appears 
to  furnish  the  least  active  digestive  fluid. 


CHYME.  225 

at  a  temperature  of  about  100°,  are,  in  an  hour  or  more, 
according  to  the  toughness  of  the  substance,  softened  and 
changed  in  just  the  same  manner  as  they  would  be  in  the 
stomach. 

The  nature  of  the  action  by  which  the  mucous  membrane  of 
the  stomach  and  its  secretion  work  these  changes  in  organic 
matter  is  exceedingly  obscure.  The  action  of  the  pepsin  may 
be  compared  with  that  of  a  ferment,  which  at  the  same  time 
that  it  undergoes  change  itself,  induces  certain  changes  also  in 
the  organic  matters  with  which  it  is  in  contact.  Or  its  mode 
of  action  may  belong  to  that  class  of  chemical  processes  termed 
"  catalytic,"  in  which  a  substance  excites,  by  its  mere  presence, 
and  without  itself  undergoing  change  as  ordinary  ferments  do, 
some  chemical  action  in  the  substances  with  which  it  is  in  con- 
tact. So,  for  example,  spongy  platinum,  or  charcoal,  placed 
in  a  mixture,  however  voluminous,  of  oxygen  and  hydrogen, 
makes  them  combine  to  form  water ;  and  diastase  makes  the 
starch  in  grains  undergo  transformation,  and  sugar  is  produced. 
And  that  pepsin  acts  in  some  such  manner  appears  probable 
from  the  very  minute  quantity  capable  of  exerting  the  peculiar 
digestive  action  on  a  large  quantity  of  food,  and  apparently 
with  little  diminution  in  its  active  power.  The  process  differs 
from  ordinary  fermentation,  in  being  unattended  with  the  for- 
mation of  carbonic  acid,  in  not  requiring  the  presence  of  oxygen, 
and  in  being  unaccompanied  by  the  production  of  new  quan- 
tities of  the  active  principle,  or  ferment.  It  agrees  with  the 
processes  of  both  fermentation  and  organic  catalysis,  in  that 
whatever  alters  the  composition  of  the  pepsin  (such  as  heat 
above  100°,  strong  alcohol,  or  strong  acids),  destroys  the  diges- 
tive power  of  the  fluid. 

Changes  of  the  Food  in  the  Stomach. 

The  general  effect  of  digestion  in  the  stomach  is  the  conver- 
sion of  the  food  into  chyme,  a  substance  of  various  composition 
according  to  the  nature  of  the  food,  yet  always  presenting  a 
characteristic  thick,  pultaceous,  grumous  consistence,  with  the 
undigested  portions  of  the  food  mixed  in  a  more  fluid  substance, 
and  a  strong,  disagreeable  acid  odor  and  taste.  Its  color  de- 
pends on  the  nature  of  the  food,  or  on  the  admixture  of  yellow 
or  green  bile  which  may,  apparently,  even  in  health,  pass  into 
the  stomach. 

Reduced  into  such  a  substance,  all  the  various  materials  of 
a  meal  may  be  mingled  together,  and  near  the  end  of  the  diges- 
tive process  hardly  admit  of  recognition  ;  but  the  experiments 
of  artificial  digestion,  and  the  examination  of  stomachs  with 


226  DIGESTION. 

fistulse,  have  illustrated  many  of  the  changes  through  which 
the  chief  alimentary  principles  pass,  and  the  times  and  modes 
in  which  they  are  severally  disposed  of.  These  must  now  be 
traced. 

The  readiness  with  which  the  gastric  fluid  acts  on  the  several 
articles  of  food  is,  in  some  measure,  determined  by  the  state  of 
division,  and  the  tenderness  and  moisture  of  the  substance  pre- 
sented to  it.  By  minute  division  of  the  food,  the  extent  of 
surface  with  which  the  digestive  fluid  can  come  in  contact  is 
increased,  and  its  action  proportionably  accelerated.  Tender 
and  moist  substances  offer  less  resistance  to  the  action  of  the 
gastric  juice  than  tough,  hard,  and  dry  ones  do,  because  they 
may  be  thoroughly  penetrated  by  it,  and  thus  be  attacked  not 
only  at  the  surface,  but  at  every  part  at  once.  The  readiness 
with  which  a  substance  is  acted  upon  by  the  gastric  fluid  does 
not,  however,  necessarily  imply  the  degree  of  its  nutritive 
property ;  for  a  substance  may  be  nutritious,  yet,  on  account 
of  its  toughness  and  other  qualities,  hard  to  digest ;  and  many 
soft,  easily  digested  substances  contain  comparatively  a  small 
amount  of  nutriment.  But  for  a  substance  to  be  nutritive,  it 
must  be  capable  of  being  assimilated  to  the  blood  ;  and  to  h'nd 
its  way  into  the  blood,  it  must,  if  insoluble,  be  digestible  by 
the  gastric  fluid  or  some  other  secretion  in  the  intestinal  canal. 
There  is,  therefore,  thus  far,  a  necessary  connection  between 
the  digestibility  of  a  substance  and  its  power  of  affording  nutri- 
ment. 

Those  portions  of  food  which  are  liquid  when  taken  into  the 
stomach,  or  which  are  easily  soluble  in  the  fluids  therein,  are 
probably  at  once  absorbed  by  the  bloodvessels  in  the  mucous 
membrane  of  the  stomach.  Magendie's  experiments,  and 
better  still,  those  of  Dr.  Beaumont,  have  proved  this  quick 
absorption  of  water,  wine,  weak  saline  solutions,  and  the  like ; 
that  they  are  absorbed  without  manifest  change  by  the  diges- 
tive fluid,  and  that,  generally,  the  water  of  such  liquid  food 
as  soups  is  absorbed  at  once,  so  that  the  substances  suspended 
in  it  are  concentrated  into  a  thicker  material,  like  the  chyme 
from  solid  food,  before  the  digestive  fluid  acts  upon  them. 

The  action  of  the  gastric  fluid  on  the  several  kinds  of  solid 
food  has  been  studied  in  various  ways.  In  the  earliest  experi- 
ments, perforated  metallic  and  glass  tubes,  filled  with  the  ali- 
mentary substances,  were  introduced  into  the  stomachs  of  ani- 
mals, and  after  the  lapse  of  a  certain  time  withdrawn,  to  ob- 
serve the  condition  of  the  contained  substances  ;  but  such  ex- 
periments are  fallacious,  because  gastric  fluid  has  not  ready 
access  to  the  food.  A  better  method  was  practiced  in  a  series 
of  experiments  by  Tiedemann  and  Gmelin,  who  fed  dogs  with 


DIGESTION    OF     FOOD    IN    THE    STOMACH.        227 

different  substances,  and  killed  them  in  a  certain  number  of 
hours  afterwards.  But  the  results  they  obtained  are  of  less 
interest  than  those  of  the  experiments  of  Dr.  Beaumont  on  his 
patient,  St.  Martin,  and  of  Dr.  Gosse,  who  had  the  power  of 
vomiting  at  will. 

Dr.  Beaumont's  observations  show,  that  the  process  of  di- 
gestion in  the  stomach,  during  health,  takes  place  so  rapidly, 
that  a  full  meal,  consisting  of  animal  and  vegetable  substances, 
may  nearly  all  be  converted  into  chyme  in  about  an  hour,  and 
the  stomach  left  empty  in  two  hours  and  a  half.  The  details 
of  two  days'  experiments  will  be  sufficient  examples : 

Exp.  42. — April  7th,  8  A.M.  St.  Martin  breakfasted  on 
three  hard-boiled  eggs,  pancakes,  and  coffee.  At  half-past 
eight  o'clock,  Dr.  Beaumont  examined  the  stomach,  and  found 
a  heterogeneous  mixture  of  the  several  articles  slightly 
digested At  a  quarter  past  ten,  no  part  of  the  break- 
fast remained  in  the  stomach. 

Exp.  43. — At  eleven  o'clock  the  same  day,  he  ate  two 
roasted  eggs  and  three  ripe  apples.  In  half  an  hour  they 
were  in  an  incipient  state  of  digestion  ;  and  a  quarter  past 
twelve  no  vestige  of  them  remained. 

Exp.  44. — At  two  o'clock  P.M.  the  same  day,  he  dined  on 
roasted  pig  and  vegetables.  At  three  o'clock  they  were  half 
chymified,  and  at  half-past  four  nothing  remained  but  a  very 
little  gastric  juice. 

Again,  Exp.  46. — April  9th.  At  three  o'clock  P.M.  he 
dined  on  boiled  dried  codfish,  potatoes,  parsnips,  bread,  and 
drawn  butter.  At  half-past  three  o'clock  examined,  and  took 
out  a  portion  about  half  digested  ;  the  potatoes  the  least  so. 
The  fish  was  broken  down  into  small  filaments ;  the  bread  and 
parsnips  were  not  to  be  distinguished.  At  four  o'clock,  ex- 
amined another  portion.  Very  few  particles  of  fish  remained 
entire.  Some  of  the  few  potatoes  were  distinctly  to  be  seen. 
At  half-past  four  o'clock,  he  took  out  and  examined  another 
portion  ;  all  completely  chymified.  At  five  o'clock  stomach 
empty. 

Many  circumstances  besides  the  nature  of  the  food  are  apt 
to  influence  the  process  of  chymification.  Among  them  are, 
the  quantity  of  food  taken  ;  the  stomach  should  be  fairly  filled, 
not  distended  :  the  time  that  has  elapsed  since  the  last  meal, 
which  should  be  at  least  enough  for  the  stomach  to  be  quite 
clear  of  food :  the  amount  of  exercise  previous  and  subsequent 
to  the  meal,  gentle  exercise  being  favorable,  overexertion  in- 
jurious to  digestion  ;  the  state  of  mind — tranquillity  of  temper 
being  apparently  essential  to  a  quick  and  due  digestion :  the 
bodily  health  :  the  state  of  the  weather.  But  under  ordinary 


228  DIGESTION. 

circumstances,  from  three  to  four  hours  may  be  taken  as  the 
average  time  occupied  by  the  digestion  of  a  meal  in  the  stom- 
ach. 

Dr.  Beaumont  constructed  a  table  showing  the  times  required 
for  the  digestion  of  all  usual  articles  of  food  in  St.  Martin's 
stomach,  and  in  his  gastric  fluid  taken  from  the  stomach. 
Among  the  substances  most  quickly  digested  were  rice  and 
tripe,  both  of  which  were  chymified  in  an  hour;  eggs,  salmon, 
trout,  apples,  and  venison,  were  digested  in  an  hour  and  a  half; 
tapioca,  barley,  milk,  liver,  fish,  in  two  hours;  turkey,  lamb, 
potatoes,  pig,  in  two  hours  and  a  half;  beef  and  mutton  re- 
quired from  three  hours  to  three  and  a  half,  and  both  were 
more  digestible  than  veal ;  fowls  were  like  mutton  in  their  de- 
gree of  digestibility.  Animal  substances  were,  in  general,  con- 
verted into  chyme  more  rapidly  than  vegetables. 

Dr.  Beaumont's  experiments  were  all  made  on  ordinary  arti- 
cles of  food.  A  minuter  examination  of  the  changes  produced 
by  gastric  digestion  on  various  tissues  has  been  made  by  Dr. 
Rawitz,  who  examined  microscopically  the  product  of  the  arti- 
ficial digestion  of  different  kinds  of  food,  and  the  contents  of 
the  faeces  after  eating  the  same  kinds  of  food.  The  general 
results  of  his  examinations,  as  regards  animal  food,  show  that 
muscular  tissue  breaks  up  into  its  constituent  fasciculi,  and 
that  these  again  are  divided  transversely;  gradually  the  trans- 
verse strife  become  indistinct,  and  then  disappear;  and  finally, 
the  sarcolemma  seems  to  be  dissolved,  and  no  trace  of  the  tissue 
can  be  found  in  the  chyme,  except  a  few  fragments  of  fibres. 
These  changes  ensue  most  rapidly  in  the  flesh  of  fish  and  hares, 
less  rapidly  in  that  of  poultry  and  other  animals.  The  cells  of 
cartilage  and  fibro-cartilage,  except  those  of  fish,  pass  unchanged 
through  the  stomach  and  intestines,  and  may  be  found  in  the 
faeces.  The  interstitial  tissues  of  these  structures  are  converted 
into  pulpy  textureless  substances  in  the  artificial  digestive  fluid, 
and  are  not  discoverable  in  the  faeces.  Elastic  fibres  are  un- 
changed in  the  digestive  fluid.  Fat-cells  are  sometimes  found 
quite  unaltered  in  the  faeces;  and  crystals  of  cholesterin  may 
usually  be  obtained  from  faeces,  especially  after  the  use  of  pork 
fat. 

As  regards  vegetable  substances,  Dr.  Rawitz  states,  that  he 
frequently  found  large  quantities  of  cell-membranes  unchanged 
in  the  faeces ;  also  starch-cells,  commonly  deprived  of  only  part 
of  their  contents.  The  green  coloring  principle,  chlorophyll, 
was  usually  unchanged.  The  walls  of  the  sap-vessels  and 
spiral-vessels  were  quite  unaltered  by  the  digestive  fluid,  and 
were  usually  found  in  large  quantities  in  the  faeces;  their  con- 
tents, probably,  were  removed. 


DIGESTION    IN    THE    STOMACH.  229 

From  these  experiments,  we  may  understand  the  structural 
changes  which  the  chief  alimentary  substances  undergo  in  their 
conversion  into  chyme;  and  the  proportions  of  each  which  are 
not  reducible  to  chyme,  nor  capable  of  any  further  act  of  di- 
gestion. The  chemical  changes  undergone  in  and  by  the  proxi- 
mate principles  are  less  easily  traced. 

Of  the  albuminous  principles,  some,  as  the  casein  of  milk, 
are  coagulated  by  the  acid  of  the  gastric  fluid;  and  thus,  be- 
fore they  are  digested,  come  into  the  condition  of  the  other 
solid  principles  of  the  food.  These,  including  solid  albumen 
and  fibrin,  in  the  same  proportion  that  they  are  broken  up  and 
anatomically  disorganized  by  the  gastric  fluid,  appear  to  be 
reduced  or  lowered  in  their  chemical  composition.  This  chemi- 
cal change  is  probaby  produced,  as  suggested  by  Dr.  Prout,  by 
the  principles  entering  into  combination  with  water.  It  is  suf- 
ficient to  conceal  nearly  all  their  characteristic  properties ;  the 
albumen  is  rendered  scarcely  coagulable  by  heat;  the  gelatin, 
even  when  its  solution  is  evaporated,  does  not  congeal  in  cool- 
ing; the  fibrin  and  casein  cannot  be  found  by  their  character- 
istic tests.  It  would  seem,  indeed,  that  all  these  various  sub- 
stances are  converted  into  one  and  the  same  principle,  a  low 
form  of  albumen,  not  precipitable  by  nitric  acid  or  heat,  and 
now  generally  termed  albuminose  or  peptone,  from  which,  after 
being  absorbed,  they  are  again  raised,  in  the  elaboration  of  the 
blood,  to  which  they  are  ultimately  assimilated. 

The  change  of  molecular  constitution  suffered  by  the  albu- 
minous parts  of  the  food,  in  consequence  of  the  action  of  the 
gastric  juice,  has  an  important  relation  to  their  absorption  by 
the  bloodvessels  of  the  stomach.  From  the  condition  of  "  col- 
loids," or  substances,  so  named  by  Professor  Graham,  which 
are  absorbed  with  extreme  difficulty,  they  appear,  from  ex- 
periments of  Funke,  to  assume  to  a  great  degree  the  char- 
acter of  "  crystalloids,"  which  can  pass  through  animal  mem- 
branes with  ease.1 

Whatever  be  the  mode  in  which  the  gastric  secretion 
affects  these  principles,  it,  or  something  like  it,  appears  essen- 
tial, in  order  that  they  may  be  assimilated  to  the  blood  and 
tissues.  For,  when  Bernard  and  Barreswil  injected  albumen 
dissolved  in  water  into  the  jugular  veins  of  dogs,  they  always 
in  about  three  hours  after,  found  it  in  the  urine.  But  if,  pre- 
vious to  injection,  it  was  mixed  with  gastric  fluid,  no  trace  of 
it  could  be  detected  in  the  urine.  The  influence  of  the  liver 
seems  to  be  almost  as  efficacious  as  that  of  the  gastric  fluid,  in 


1  These  terms  will    be    further  explained  and   illustrated    in   the 
chapter  on  Absorption. 

20 


230  DIGESTION. 

rendering  albumen  assimilable;  for  Bernard  found  that,  if 
diluted  egg-albumen,  unmixed  with  gastric  fluid,  is  injected 
into  the  portal  vein,  it  no  longer  makes  its  appearance  in 
the  urine,  and  is,  therefore,  no  doubt,  assimilated  by  the  blood. 

Probably,  most  of  the  albuminose,  with  other  soluble  and 
fluid  materials,  is  absorbed  directly  from  the  stomach  by  the 
minute  bloodvessels  with  which  the  mucous  membrane  is  so 
abundantly  supplied. 

The  saccharine  including  the  amylaceous  principles  are  at 
first,  probably,  only  mechanically  separated  from  the  vege- 
table substances  within  which  they  are  contained,  by  the 
action  of  the  gastric  fluid.  The  soluble  portions,  viz.,  dextrin 
and  sugar,  are  probably  at  once  absorbed.  The  insoluble 
ones,  viz.,  starch  and  lignin  (or  some  parts  of  them),  are  ren- 
dered soluble  and  capable  of  absorption,  by  being  converted 
into  dextrin  or  grape-sugar.  It  is  probable  that  this  change 
is  carried  on  to  some  extent  in  the  stomach  ;  but  this  conver- 
sion of  starch  into  sugar  is  effected,  not  by  the  gastric  fluid, 
but  by  the  saliva  introduced  with  the  food,  or  subsequently 
swallowed.  The  transformation  of  starch  is  continued  in  the 
intestinal  canal,  as  will  be  shown,  by  the  secretion  of  the  pan- 
creas, and  perhaps  by  that  of  the  intestinal  glands  and  mu- 
cous membrane.  The  power  of  digesting  uncooked  starch  is, 
however,  very  limited  in  man  and  Carnivora,  for  when  starch 
has  been  taken  raw,  as  in  corn  and  rice,  large  quantities  of 
the  granules  are  passed  unaltered  with  the  excrements.  Cook- 
ing, by  expanding  or  bursting  the  envelopes  of  the  granules, 
renders  their  interior  more  amenable  to  the  action  of  the  di- 
gestive organs ;  and  the  abundant  nutriment  furnished  by 
bread,  and  the  large  proportion  that  is  absorbed  of  the  weight 
consumed,  afford  proof  of  the  completeness  of  their  power  to 
make  its  starch  soluble  and  prepare  it  for  absorption. 

Of  the  oleaginous  principles, — as  to  their  changes  in  the 
stomach,  no  more  can  be  said  than  that  they  appear  to  be 
reduced  to  minute  particles,  and  pass  into  the  intestines  min- 
gled with  the  other  constituents  of  the  chyme.  In  the  case 
of  the  solid  fats,  this  effect  is  probably  produced  by  the  sol- 
vent action  of  the  gastric  juice  on  the  areolar  tissue,  albumin- 
ous cell -walls,  &c.,  which  enter  into  their  composition,  and  by 
the  solution  of  which  the  true  fat  is  able  to  mingle  more  uni- 
formly with  the  other  constituents  of  the  chyme.  Being  fur- 
ther changed  in  the  intestinal  canal,  fat  is  rendered  capable 
of  absorption  by  the  lacteals. 


MOVEMENTS    OF    THE    STOMACH.  231 


Movements  of  the  Stomach. 

It  has  been  already  said,  that  the  gastric  fluid  is  assisted  in 
accomplishing  its  share  in  digestion  by  the  movements  of  the 
stomach.  In  granivorous  birds,  for  example,  the  contraction 
of  the  strong  muscular  gizzard  affords  a  necessary  aid  to  di- 
gestion, by  grinding  and  triturating  the  hard  seeds  which  con- 
stitute part  of  the  food.  But  in  the  stomachs  of  man  and 
Mammalia  the  motions  of  the  muscular  coat  are  too  feeble  to 
exercise  any  such  mechanical  force  on  the  food  ;  neither  are 
they  needed,  for  mastication  has  already  done  the  mechanical 
work  of  a  gizzard ;  and  the  experiments  of  Reaumur  and 
Spallanzani  have  demonstrated  that  substances  inclosed  in 
perforated  tubes,  and  consequently  protected  from  mechanical 
influence,  are  yet  digested. 

The  normal  actions  of  the  muscular  fibres  of  the  human 
stomach  appear  to  have  a  threefold  purpose :  first,  to  adapt 
the  stomach  to  the  quantity  of  food  in  it,  so  that  its  walls  may 
be  in  contact  with  the  food  on  all  sides,  and,  at  the  same  time, 
may  exercise  a  certain  amount  of  compression  upon  it ; 
secondly,  to  keep  the  orifices  of  the  stomach  closed  until  the 
food  is  digested  ;  and,  thirdly,  to  perform  certain  peristaltic 
movements,  whereby  the  food,  as  it  becomes  chymified,  is 
gradually  propelled  towards,  and  ultimately  through,  the  py- 
lorus. In  accomplishing  this  latter  end,  the  movements  with- 
out doubt  materially  contribute  towards  effecting  a  thorough 
intermingling  of  the  food  and  the  gastric  fluid. 

When  digestion  is  not  going  on,  the  stomach  is  uniformly 
contracted,  its  orifices  not  more  firmly  than  the  rest  of  its 
walls  ;  but,  if  examined  shortly  after  the  introduction  of  food, 
it  is  found  closely  encircling  its  contents,  and  its  orifices  are 
firmly  closed  like  sphincters.  The  cardiac  orifice,  every  time 
food  is  swallowed,  opens  to  admit  its  passage  to  the  stom- 
ach, and  immediately  again  closes.  The  pyloric  orifice, 
during  the  first  part  of  gastric  digestion,  is  usually  so  com- 
pletely closed,  that  even  when  the  stomach  is  separated  from 
the  intestines,  none  of  its  contents  escape.  But  towards  the 
termination  of  the  digestive  process,  the  pylorus  seems  to  offer 
less  resistance  to  the  passage  of  substances  from  the  stomach ; 
first  it  yields  to  allow  the  successively  digested  portions  to  go 
through  it ;  and  then  it  allows  the  transit  of  even  undigested 
substances. 

From  the  observations  of  Dr.  Beaumont  on  the  man  St. 
Martin,  it  appears  that  food,  so  soon  as  it  enters  the  stomach, 
is  subjected  to  a  kind  of  peristaltic  action  of  the  muscular 
coat,  whereby  the  digested  portions  are  gradually  approxi- 


232  DIGESTION. 

mated  towards  the  pylorus.  The  movements  were  observed 
to  increase  in  rapidity  as  the  process  of 'chymification  advanced, 
and  were  continued  until  it  was  completed. 

The  contraction  of  the  fibres  situated  towards  the  pyloric 
end  of  the  stomach  seems  to  be  more  energetic  and  more  de- 
cidedly peristaltic  than  those  of  the  cardiac  portion.  Thus, 
Dr.  Beaumont  found  that  when  the  bulb  of  the  thermometer 
was  placed  about  three  inches  from  the  pylorus,  it  was  tightly 
embraced  from  time  to  time  and  drawn  towards  the  pyloric 
orifice  for  a  distance  of  three  or  four  inches.  The  object  of 
this  movement  appears  to  be,  as  just  said,  to  carry  the  food  to- 
wards the  pylorus  as  fast  as  it  is  formed  into  chyme,  and  to 
propel  the  chyme  into  the  duodenum  ;  the  undigested  portions 
of  food  being  kept  back  until  they  are  also  reduced  into 
chyme,  or  until  all  that  is  digestible  has  passed  out.  The  ac- 
tion of  these  fibres  is  often  seen  in  the  contracted  state  of  the 
pyloric  portion  of  the  stomach  after  death,  when  it  alone  is 
contracted  and  firm,  while  the  cardiac  portion  forms  a  dilated 
sac.  Sometimes,  by  a  predominant  action  of  strong  circular 
fibres  placed  between  the  cardia  and  pylorus,  the  two  por- 
tions, or  ends  as  they  are  called,  of  the  stomach,  are  separated 
from  each  other  by  a  kind  of  hour-glass  contraction. 

The  interesting  researches  of  Dr.  Brinton  have  clearly  es- 
tablished that,  by  means  of  this  peristaltic  action  of  the  mus- 
cular coats  of  the  stomach,  not  merely  is  chymified  food 
gradually  propelled  through  the  pylorus,  but  a  kind  of  double 
current  is  continually  kept  up  among  the  contents  of  the  stom- 
ach, the  circumferential  parts  of  the  mass  being  gradually 
moved  onward  towards  the  pylorus  by  the  peristaltic  contrac- 
tion of  the  muscular  fibres,  while  the  central  portions  are  pro- 
pelled in  the  opposite  direction,  namely,  towards  the  cardiac 
orifice ;  in  this  way  is  kept  up  a  constant  circulation  of  the 
contents  of  the  viscus,  highly  conducive  to  their  free  mixture 
with  the  gastric  fluid  and  to  their  ready  digestion. 

These  actions  of  the  stomach  are  peculiar  to  it  and  indepen- 
dent. But  it  is,  also,  adapted  to  act  in  concert  with  the  ab- 
dominal muscles,  in  certain  circumstances  which  can  hardly 
be  called  abnormal,  as  in  vomiting  and  eructation.  It  has 
indeed  been  frequently  stated  that  the  stomach  itself  is  quite 
passive  during  vomiting,  and  that  the  expulsion  of  its  contents 
is  effected  solely  by  the  pressure  exerted  upon  it  when  the  ca- 
pacity of  the  abdomen  is  diminished  by  the  contraction  of  the 
diaphragm,  and  subsequently  of  the  abdominal  muscles.  The 
experiments  and  observations,  however,  which  are  supposed  to 
confirm  this  statement,  only  show  that  the  contraction  of  the 
abdominal  muscles  alone  is  sufficient  to  expel  matters,  from  an 


MOVEMENTS    OF    THE    STOMACH.  233 

unresisting  bag  through  the  oesophagus ;  and  that,  under  very 
abnormal  circumstances,  the  stomach,  by  itself,  cannot  or  rather 
does  not  expel  its  contents.  They  by  no  means  show  that  in 
ordinary  vomiting  the  stomach  is  passive ;  and,  on  the  other 
hand,  there  are  good  reasons  for  believing  the  contrary. 

It  is  true  that  facts  are  wanting  to  demonstrate  with  cer- 
tainty this  action  of  the  stomach  in  vomiting  ;  but  some  of  the 
cases  of  fistulous  opening  into  the  organ  appear  to  support  the 
belief  that  it  does  take  place  ;l  and  the  analogy  of  the  case  of 
the  stomach  with  that  of  the  other  hollow  viscera,  as  the  rec- 
tum and  bladder,  may  be  also  cited  in  confirmation. 

Besides  the  influence  which  it  may  thus  have  by  its  contrac- 
tion, the  stomach  also  essentially  contributes  to  the  act  of 
vomiting,  by  the  contraction  of  its  pyloric  orifice  at  the  same 
time  that  the  oblique  fibres  around  the  cardiac  orifice  are  re- 
laxed. For,  until  the  relaxation  of  these  fibres,  no  vomiting 
can  ensue ;  when  contracted,  they  can  as  well  resist  all  the 
force  of  the  contracting  abdominal  and  other  muscles,  as  the 
muscles  by  which  the  glottis  is  closed  can  resist  the  same  force 
in  the  act  of  straining.  Doubtless  we  may  refer  many  of  the 
acts  of  retching  and  ineffectual  attempts  to  vomit,  to  the  want 
of  concord  between  the  relaxation  of  these  muscles  and  the  con- 
traction of  the  others. 

The  muscles  with  which  the  stomach  co-operates  in  contrac- 
tion during  vomiting,  are  chiefly  and  primarily  those  of  the 
abdomen  ;  the  diaphragm  also  acts,  but  not  as  the  muscles  of 
the  abdominal  walls  do.  They  contract  and  compress  the 
stomach  more  and  more  towards  the  back  and  upper  parts  of 
the  diaphragm ;  and  the  diaphragm  (which  is  usually  drawn 
down  in  the  deep  inspiration  that  precedes  each  act  of  vomit- 
ing) holds  itself  fixed  in  contraction,  and  presents  an  unyield- 
ing surface  against  which  the  stomach  may  be  pressed.  It  is 
enabled  to  act  thus,  and  probably  only  thus,  because  the  in- 
spiration which  precedes  the  act  of  vomiting  is  terminated  by 
the  closure  of  the  glottis;  after  which  the  diaphragm  can 
neither  descend  further,  except  by  expanding  the  air  in  the 
lungs,  nor,  except  by  compressing  the  air,  ascend  again  until, 
the  act  of  vomiting  having  ceased,  the  glottis  is  opened  again 
(see  diagram,  p.  181 ;  see  also  p.  183). 

Some  persons  possess  the  power  of  vomiting  at  will,  without 
applying  any  undue  irritation  to  the'stomach,  but  simply  by  a 
voluntary  effort,  It  seems  also,  that  this  piower  may  be  ac- 

1  A  collodion  of  cases  of  fistulous  communication  with  the  stomach, 
through  the  abdominal  parietes,  has  been  given  by  Dr.  Murchison  in 
vol,  $lj  of  the  Medico-Chirurgical  Transactions, 


234  DIGESTION. 

quired  by  those  who  do  not  naturally  possess  it,  and  by  con- 
tinual practice  may  become  a  habit.  There  are  cases  also  of 
rare  occurrence  in  which  persons  habitually  swallow  their  food 
hastily,  and  nearly  unmasticated,  and  then  at  their  leisure  re- 
gurgitate it,  piece  by  piece,  into  their  mouth,  remasticate,  and 
again  swallow  it,  exactly  as  is  done  by  the  ruminant  order  of 
Mammalia. 

Influence  of  the  Nervous  System  on  Gastric  Digestion. 

This  influence  is  manifold;  and  is  evidenced,  1st,  in  the  sen- 
sations which  induce  to  the  taking  of  food  ;  2d,  in  the  secretion 
of  the  gastric  fluid;  3d,  in  the  movements  of  the  food  in  and 
from  the  stomach. 

The  sensation  of  hunger  is  manifested  in  consequence  of  de- 
ficiency of  food  in  the  system.  The  mind  refers  the  sensation 
to  the  stomach ;  yet  since  the  sensation  is  relieved  by  the  in- 
troduction of  food  either  into  the  stomach  itself,  or  into  the 
blood  through  other  channels  than  the  stomach,  it  would  ap- 
pear not  to  depend  on  the  state  of  the  stomach  alone.  This 
view  is  confirmed  by  the  fact,  that  the  division  of  both  pneu- 
mogastric  nerves,  which  are  the  principal  channels  by  which 
the  mind  is  cognizant  of  the  condition  of  the  stomach,  does  not 
appear  to  allay  the  sensations  of  hunger. 

But  that  the  stomach  has  some  share  in  this  sensation  is 
proved  by  the  relief  afforded,  though  only  temporarily,  by  the 
introduction  of  even  non-alimentary  substances  into  this  organ. 
It  may,  therefore,  be  said  that  the  sensation  of  hunger  is  de- 
rived from  the  system  generally,  but  chiefly  from  the  condition 
of  the  stomach,  the  nerves  of  which,  we  may  suppose,  are  more 
affected  by  the  state  of  the  insufficiently  replenished  blood  than 
those  of  other  organs  are. 

The  sensation  of  thirst,  indicating  the  want  of  fluid,  is  re- 
ferred to  the  fauces,  although,  as  in  hunger,  this  is  merely  the 
local  declaration  of  a  general  condition  existing  in  the  system. 
For  thirst  is  relieved  for  only  a  very  short  time  by  moistening 
the  dry  fauces ;  but  may  be  relieved  completely  by  the  intro- 
duction of  liquids  into  the  blood,  either  through  the  stomach, 
or  by  injections  into  the  bloodvessels,  or  by  absorption  from 
the  surface  of  the  skin  or  the  intestines.  The  sensation  of 
thirst  is  perceived  most  naturally  whenever  there  is  a  dispro- 
portionately small  quantity  of  water  in  the  blood;  as  well, 
therefore,  when  water  has  been  abstracted  from  the  blood,  as 
when  saline  or  any  solid  matters  have  been  abundantly  added 
to  it.  We  can  express  the  fact  (even  if  it  be  not  an  explana- 
tion of  it),  by  saying  that  the  nerves  of  the  mouth  and  i'auces, 


INFLUENCE    OF    THE    NERVOUS    SYSTEM.       235 

through  which  the  sense  of  thirst  is  chiefly  derived,  are  more  sen- 
sitive to  this  condition  of  the  blood  than  other  nerves  are.  And 
the  cases  of  hunger  and  thirst  are  not  the  only  ones  in  which 
the  mind  derives,  from  certain  organs,  a  peculiar  predominant 
sensation  of  some  condition  affecting  the  whole  body.  Thus, 
the  sensation  of  the  "  necessity  of  breathing,"  is  referred  es- 
pecially to  the  lungs ;  but,  as  Volkmann's  experiments  show, 
it  depends  on  the  condition  of  the  blood  which  circulates  every- 
where, and  is  felt  even  after  the  lungs  of  animals  are  removed  ; 
for  they  continue,  even  then,  to  gasp  and  manifest  the  sensa- 
tion of  want  of  breath.  And,  as  with  respiration  when  the 
lungs  are  removed,  the  mind  may  still  feel  the  body's  want  of 
breath ;  so  in  hunger  and  thirst,  even  when  the  stomach  has 
been  filled  with  innutritions  substances,  or  the  pneumogastric 
nerves  have  been  divided,  and  the  mouth  and  fauces  are  kept 
moist,  the  mind  is  still  aware,  by  the  more  obscure  sensations 
in  other  parts,  of  the  whole  body's  need  of  food  and  water. 

The  influence  of  the  nervous  system  on  the  secretion  of  gastric 
fluid,  is  shown  plainly  enough  in  the  influence  of  the  mind 
upon  digestion  in  the  stomach ;  and  is,  in  this  regard,  well 
illustrated  by  several  of  Dr.  Beaumont's  observations.  M. 
Bernard  also,  watching  the  act  of  gastric  digestion  in  dogs 
which  had  fistulous  openings  into  their  stomachs,  saw  that  on 
the  instant  of  dividing  their  pneumogastric  nerves,  the  process 
of  digestion  was  stopped,  and  the  mucous  membrane  of  the 
stomach,  previously  turgid  with  blood,  became  pale,  and  ceased 
to  secrete.  These,  however,  and  the  like  experiments  showing 
the  instant  effect  of  division  of  the  pneumogastric  nerves,  may 
prove  no  more  than  the  effect  of  a  severe  shock,  and  the  fact 
that  influences  affecting  digestion  may  be  conveyed  to  the 
stomach  through  those  nerves.  From  other  experiments  it 
may  be  gathered,  that  although,  as  in  M.  Bernard's,  the  division 
of  both  pneumogastric  nerves  always  temporarily  suspends  the 
secretion  of  gastric  fluid,  and  so  arrests  the  process  of  digestion, 
and  is  occasionally  followed  by  death  from  inanition  ;  yet  the 
digestive  powers  of  the  stomach  may  be  completely  restored 
after  the  operation,  and  the  formation  of  chyme  and  the  nutri- 
tion of  the  animal  may  be  carried  on  almost  as  perfectly  as  in 
health. 

In  thirty  experiments  on  Mammalia,  which  M.  Wernscheidt 
performed  under  Miiller's  direction,  not  the  least  difference 
could  be  perceived  in  the  action  of  narcotic  poisons  introduced 
into  the  stomach,  whether  the  pneumogastric  had  been  divided 
on  both  sides  or  not,  provided  the  animals  were  of  the  same 
species  and  size.  It  appears,  however,  that  such  poisons  as  are 
capable  of  being  rendered  inert  by  the  action  of  the  gastric 


236  DIGESTION. 

fluid,  may,  if  taken  into  the  stomach  shortly  after  division  of 
both  pneumogastric  nerves,  produce  their  poisonous  effects;  in 
consequence,  apparently,  of  the  temporary  suspension  of  the 
secretion  of  gastric  fluid.  Thus,  in  one  of  his  experiments,  M. 
Bernard  gave  to  each  of  two  dogs,  in  one  of  which  he  had  di- 
vided the  pneumogastric  nerves,  a  dose  of  emulsin,  and  half 
an  hour  afterwards  a  dose  of  amygdalin,  substances  which 
are  innocent  alone,  but  when  mixed  produce  hydrocyanic  acid. 
The  dog  whose  nerves  were  cut,  died  in  a  quarter  of  an  hour, 
the  substances  being  absorbed  unaltered  and  mixing  in  the 
blood;  in  the  other,  the  emulsin  was  decomposed  by  the  gas- 
tric fluid  before  the  amygdalin  was  administered;  therefore, 
hydrocyanic  acid  was  not  formed  in  the  blood,  and  the  dog 
survived. 

The  influence  of  the  pneumogastric  nerves  over  the  secretion 
of  gastric  fluid  has  been  of  late  even  more  decidedly  shown  by 
M.  Bernard,  who  found  that  galvanic  stimulus  of  these  nerves 
excited  an  active  secretion  of  the  fluid,  while  a  like  stimulus 
applied  to  the  sympathetic  nerves  issuing  from  the  semilunar 
ganglia,  caused  a  diminution  and  even  complete  arrest  of  the 
secretion. 

The  influence  of  the  nervous  system  on  the  movements  of  the 
stomach  has  been  often  seen  in  the  retardation  or  arrest  of  these 
movements  after  division  of  the  pneumogastric  nerves.  The 
results  of  irritating  the  same  nerves  were  ambiguous ;  but  the 
experiments  of  Longet  and  Bischoff  have  shown  that  the  dif- 
ferent results  depended  on  whether  the  stomach  were  digesting 
or  not  at  the  time  of  the  experiment.  In  the  act  of  digestion, 
the  nervous  system  of  the  stomach  appears  to  participate  in 
the  excitement  which  prevails  through  the  rest  of  its  organiza- 
tion, and  a  stimulus  applied  to  the  pneumogastric  nerves  is  felt 
intensely,  and  active  movements  of  the  muscular  fibres  of  the 
stomach  follow;  but  in  the  inaction  of  fasting,  the  same  stimu- 
lus produces  no  effect.  So,  while  the  stomach  is  digesting,  the 
pylorus  is  too  irritable  to  allow  anything  but  chyme  to  pass; 
but  when  digestion  is  ended,  the  undigested  parts  of  the  food, 
and  even  large  bodies,  coins,  and  the  like,  may  pass  through  it. 

Digestion  of  the  Stomach  after  Death. 

If  an  animal  die  during  the  process  of  gastric  digestion,  and 
when,  therefore,  a  quantity  of  gastric  juice  is  present  in  the 
interior  of  the  stomach,  the  walls  of  this  organ  itself  are  fre- 
quently themselves  acted  on  by  their  own  secretion,  and  to 
such  an  extent,  that  a  perforation  of  considerable  size  may  be 
produced,  and  the  contents  of  the  stomach  may  in  part  escape 


POST-MORTEM     DIGESTION.  237 

into  the  cavity  of  the  abdomen.  This  phenomenon  is  not  un- 
frequently  observed  in  post-mortem  examinations  of  the  human 
body;  but,  as  Dr.  Pavy  observes,  the  effect  may  be  rendered, 
by  experiment,  more  strikingly  manifest.  "If,  for  instance," 
he  remarks,  "an  animal,  as  a  rabbit,  be  killed  at  a  period  of 
digestion,  and  afterwards  exposed  to  artificial  warmth  to  pre- 
vent its  temperature  from  falling,  not  only  the  stomach,  but 
many  of  the  surrounding  parts  will  be  found  to  have  been  dis- 
solved. With  a  rabbit  killed  in  the  evening,  and  placed  in  a 
warm  situation  (100°  to  110°  Fahr.)  during  the  night,  I  have 
seen  in  the  morning,  the  stomach,  diaphragm,  part  of  the  liver 
and  lungs,  and  the  intercostal  muscles  of  the  side  upon  which 
the  animal  was  laid  all  digested  away,  with  the  muscles  and 
skin  of  the  neck  and  upper  extremity  on  the  same  side  also  in 
a  semi-digested  state." 

From  these  facts,  it  becomes  an  interesting  question  why, 
during  life,  the  stomach  is  free  from  liability  to  injury  from  a 
secretion,  which,  after  death,  is  capable  of  such  destructive 
effects  ?  John  Hunter,  who  particularly  drew  attention  to  the 
phenomena  of  post-mortem  digestion,  explained  the  immunity 
from  injury  of  the  living  stomach,  by  referring  it  to  the  pro- 
tective influence  of  the  "vital  principle."  But  this  dictum 
has  been  called  in  question  by  subsequent  observers.  It  is, 
indeed,  rather  a  statement  of  a  fact,  than  an  explanation 
of  its  cause.  It  must  be  confessed,  however,  that  no  entirely 
satisfactory  theory  has  been  yet  stated  as  a  substitute. 

It  is  only  necessary  to  refer  to  the  idea  of  Bernard,  that  the 
living  stomach  finds  protection  from  its  secretion  in  the  pres- 
ence of  epithelium  and  mucus,  which  are  constantly  renewed 
in  the  same  degree  that  they  are  constantly  dissolved,  in  order 
to  remark  that  this  theory  has  been  disproved  by  experiments 
of  Pavy's,  in  which  the  mucous  membrane  of  the  stomachs  of 
dogs  was  dissected  off  for  a  small  space,  and,  on  killing  the 
animals  some  days  afterwards,  no  sign  of  digestion  of  the 
stomach  was  visible.  "  Upon  one  occasion,  after  removing  the 
mucous  membrane  and  exposing  the  muscular  fibres  over  a 
space  of  about  an  inch  and  a  half  in  diameter,  the  animal  was 
allowed  to  live  for  ten  days.  It  ate  food  every  day,  and 
seemed  scarcely  affected  by  the  operation.  Life  was  destroyed 
whilst  digestion  was  being  carried  on,  and  the  lesion  in  the 
stomach  was  found  very  nearly  repaired :  new  matter  had 
been  deposited  in  the  place  of  what  had  been  removed,  and 
the  denuded  spot  had  contracted  to  much  less  than  its  original 
dimensions." 

Dr.  Pavy  believes  that  the  natural  alkalinity  of  the  blood, 
which  circulates  so  freely  during  life  in  the  walls  of  the  stom- 


238  DIGESTION. 

ach,  is  sufficient  to  neutralize  the  acidity  of  the  gastric  juice, 
were  it,  so  to  speak,  to  make  an  attempt  at  digesting  parts 
with  which  it  has  no  business ;  and  as  may  be  gathered  from 
what  has  been  previously  said  (p.  228),  the  neutralization  of 
the  acidity  of  the  gastric  secretion  is  quite  sufficient  to  destroy 
its  digestive  powers.  He  also  very  ingeniously  argues  that 
this  very  alkalinity  must,  from  the  conditions  of  the  circula- 
tion naturally  existing  in  the  walls  of  the  stomach,  be  in- 
creased in  proportion  to  the  need  of  its  protective  influence. 
"  In  the  arrangement  of  the  vascular  supply,"  he  remarks,  "  a 
doubly  effective  barrier  is,  as  it  were,  provided.  The  vessels 
pass  from  below  upwards  towards  the  surface :  capillaries 
having  this  direction  ramify  between  the  tubules  by  which 
the  acid  of  the  gastric  juice  is  secreted  ;  and  being  separated 
by  secretion  below,  must  leave  the  blood  that  is  proceeding 
upwards  correspondingly  increased  in  alkalinity ;  and  thus, 
at  the  period  when  the  largest  amount  of  acid  is  flowing  into 
the  stomach,  and  the  greatest  protection  is  required,  then  is 
the  provision  afforded  in  its  highest  state  of  efficiency." 

Dr.  Pavy's  theory  is  the  best  and  most  ingenious  hitherto 
framed  in  connection  with  this  subject;  but  the  experiments 
adduced  in  its  favor  are  open  to  many  objections,  and  afford 
only  a  negative  support  to  the  conclusions  they  are  intended 
to  prove.  The  matter,  therefore,  can  scarcely  be  considered 
finally  settled. 

DIGESTION    IN   THE   INTESTINES. 

The  intestinal  canal  is  divided  into  two  chief  portions, 
named,  from  their  differences  in  diameter,  the  small  and  large 
intestine.  These  are  continuous  with  each  other,  and  com- 
municate by  means  of  an  opening  guarded  by  a  valve,  the 
ileo-ccecal  valve,  which  allows  the  passage  of  the  products  of 
digestion  from  the  small  into  the  large  bowel,  but  not,  under 
ordinary  circumstances,  in  the  opposite  direction. 

The  structure  and  functions  of  each  organ  or  tissue  con- 
cerned in  intestinal  digestion  will  be  first  described  in  detail, 
and  afterwards  a  summary  will  be  given  of  the  changes  which 
the  food  undergoes  in  its  passage  through  the  intestines,  1st, 
from  the  pylorus  to  the  ileo-csecal  valve ;  and,  2d,  from  the 
ileo-csecal  valve  to  the  anus. 

Structure  arid  Secretions  of  the  Small  Intestine. 

The  small  intestine,  the  average  length  of  which  in  an 
adult  is  about  twenty  feet,  has  been  divided,  for  convenience 


DIGESTION     IN    THE     INTESTINES. 


239 


of  description,  into  three  portions,  viz.,  the  duodenum,  which 
extends  for  eight  or  ten  inches  beyond  the  pylorus  ;  the  jeju- 
num, which  occupies  two-fifths,  and  the  ileum,  which  occupies 
three-fifths  of  the  rest  of  the  canal. 

The  small  intestine,  like  the  stomach,  is  constructed  of  three 
principal  coats,  viz.,  the  serous,  muscular,  and  mucous.  The 
serous  coat,  formed  by  the  visceral  layer  of  the  peritoneum, 
need  not  be  here  specially  described.  The  fibres  of  the  mus- 
cular coat  of  the  small  intestine  are  arranged  in  two  layers ; 
those  of  the  outer  layer  being  disposed  longitudinally  ;  those 
of  the  inner  layer  transversely,  or  in  portions  of  circles  encom- 
passing the  canal.  They  are  composed  of  the  unstriped  kind 
of  muscular  fibre. 

Between  the  mucous  and  muscular  coats,  there  is  a  layer 
of  submucous  tissue,  in  which  numerous  bloodvessels  and  a 
rich  plexus  of  nerves  and  ganglia  are  imbedded  (Meissner). 

The  mucous  membrane  is  the  most  important  coat  in  relation 
to  the  function  of  digestion.  The  following  structures  which 
enter  into  the  composition  of  the  mucous  membrane  may  be 
now  successively  described  :  the  valvulce  conniventes ;  the  wlli ; 
and  the  glands.  The  general  structure  of  the  mucous  mem- 
brane of  the  intestines  resembles  that  of  the  stomach  (p.  215), 
and,  like  it,  is  lined  on  its  inner  surface  by  columnar  epithe- 
lium. Lymphoid  or  Retiform  tissue  (Fig.  72)  enters  largely 

FIG.  72. 


The  figure  represents  a  cross-section  of  a  small  fragment  of  the  mucous  mem- 
brane, including  one  entire  crypt  of  Lieberkiihn  and  parts  of  several  others;  a, 
cavity  of  the  tubular  glands  or  crypts ;  b,  one  of  the  lining  epithelial  cells ;  c,  the 
lymphoid  or  retiforni  spaces,  of  which  some  are  empty,  and  others  occupied  by 
lymph  cells,  as  at  d. 

into  its  construction ;  and  on  its  deep  surface  is  a  layer  of  the 
muscular  is  mucosce  (p.  216). 


240 


DIGESTION. 


FIG.  73. 


Valvulce  Conniventes. 

The  valvulse  conniventes  commence  in  the  duodenum, 
about  one  or  two  inches  beyond  the  pylorus,  and  becoming 
larger  and  more  numerous  immediately  beyond  the  entrance 
of  the  bile-duct,  continue  thickly  arranged  and  well  developed 
throughout  the  jejunum ;  then,  gradually  diminishing  in  size 
and  number,  they  cease  near  the  middle  of  the  ileum.  In 
structure  they  are  formed  by  a  doubling  inwards  of  the  mu- 
cous membrane,  the  crescentic,  nearly  circular,  folds  thus 
formed  being  arranged  transversely  with  regard  to  the  axis 
of  the  intestine,  and  each  individual  fold  seldom  extending 
around  more  than  £  or  f  of  the  bowel's  circumference.  Un- 
like the  rugae  in  the  stomach,  they  do  not  disappear  on  dis- 
tension. Only  an  imperfect  notion  of 
their  natural  position  and  function  can 
be  obtained  by  looking  at  them  after  the 
intestine  has  been  laid  open  in  the  usual 
manner.  To  understand  them  aright, 
a  piece  of  gut  should  be  distended 
either  with  air  or  alcohol,  and  not 
opened  until  the  tissues  have  become 
hardened.  On  then  making  a  section, 
it  may  be  seen  that  instead  of  disap- 
pearing, as  the  rugae  in  the  stomach 
would  under  similar  circumstances,  they 
stand  out  at  right  angles  to  the  general 
surface  of  the  mucous  membrane  (Fig. 
73).  Their  functions  are  probably 
these:  Besides  (1)  offering  a  largely 
increased  surface  for  secretion  and  ab- 
sorption, they  probably  (2)  prevent  the 
too  rapid  passage  of  the  very  liquid 
products  of  gastric  digestion,  immedi- 
ately after  their  escape  from  the  stom- 

hardeued   by   alcohol)  laid  b  -.     /ON    -,        .-,     .  ,.  j 

open  to   show   the  normal      ach>  and    (3)>  b7  their   Projection,    and 

position  of  the  vaivuise  con-     consequent     interference   with   a    uni- 

niventes.  form  and  untroubled  current   of    the 

intestinal   contents,  probably   assist   in 

the  more  perfect  mingling  of  the  latter  with  the  secretions 
poured  out  to  act  on  them. 

Glands  of  the  Small  Intestine. — The  glands  are  of  three  prin- 
cipal kinds,  named  after  their  describers,  the  glands  of  Lieber- 
kiihn,  of  Peyer,  and  of  Brunn.  The  glands  or  follicles  of 
I/ieberkilhn  are  simple  tubular  depressions  of  the  intestinal 


Piece  of  small    intestine 
(previously   distended    and 


PEYERS    GLANDS. 


241 


FIG  74. 


mucous  membrane,  thickly  distributed  over  the  whole  surface 
both  of  the  large  and  small  intestines.  In  the 
small  intestine  they  are  visible  only  with  the 
aid  of  a  lens ;  and  their  orifices  appear  as  mi- 
nute dots  scattered  between  the  villi.  They 
are  larger  in  the  large  intestine,  and  increase 
in  size  the  nearer  they  approach  the  anal  end 
of  the  intestinal  tube ;  and  in  the  rectum  their 
orifices  may  be  visible  to  the  naked  eye.  In 
length  they  vary  from  ^0  to  ^  of  a  line.  Each 
tubule  (Fig.  74)  is  constructed  of  the  same  es- 
sential parts  as  the  intestinal  mucous  mem- 
brane, viz.,  a  fine  structureless  membrana  pro- 
pria,  or  basement-membrane,  a  layer  of  cylin- 
drical epithelium  lining  it,  and  capillary  blood- 
vessels covering  its  exterior.  Their  contents 
appear  to  vary,  even  in  health ;  the  varieties 
being  dependent,  probably,  on  the  period  of 
time  in  relation  to  digestion  at  which  they  are 
examined.  At  the  bottom  of  the  follicle,  the 
contents  usually  consist  of  a  granular  material,  in  which  a 
few  cytoblasts  or  nuclei  are  imbedded;  these  cytoblasts,  as 
they  ascend  towards  the  surface,  are  supposed  to  be  gradually 
developed  into  nucleated  cells,  some  of  which  are  discharged 
into  the  intestinal  cavity.  The  purpose  served  by  the  material 
secreted  by  these  glands  is  still  doubtful.  Their  large  number 
and  the  extent  of  surface  occupied  by  them,  seem,  however, 
to  indicate  that  they  are  concerned  in  other  and  higher  offices 
than  the  mere  production  of  fluid  to  moisten  the  surface  of  the 
mucous  membrane,  although,  doubtless,  this  is  one  of  their 
functions. 

The  glands  of  Peyer  occur  exclusively  in  the  small  intestine. 
They  are  found  in  greatest  abundance  in  the  lower  part  of  the 
ileum  near  to  the  ileo-csecal  valve.  They  are  met  with  in  two 
conditions,  viz.,  either  scattered  singly,  in  which  case  they  are 
termed  glandulce  solitaries,  or  aggregated  in  groups  varying 
from  one  to  three  inches  in  length  and  about  half  an  inch  in 
width,  chiefly  of  an  oval  form,  their  long  axis  parallel  with 
that  of  the  intestine.  In  this  state  they  are  named  glandulce 
agininatce,  the  groups  being  commonly  called  Peyer's  patches 
(Fig.  75).  The  latter  are  placed  almost  always  opposite  the 
attachment  of  the  mesentery.  In  structure,  and  probably  in 
function,  there  is  no  essential  difference  between  the  solitary 
glands  and  the  individual  bodies  of  which  each  group  or  patch 
is  made  up;  but  the  surface  of  the  solitary  glands  (Fig.  76)  is 
beset  with  villi,  from  which  those  forming  the  agminate 


242 


DIGESTION. 


patches  (Fig.  77)  are  usually  free.  In  the  condition  in  which 
they  have  been  most  commonly  examined,  each  gland  appears 
as  a  circular  opaque-white  sacculus,  from  half  a  line  to  a  line 


Agminate  follicles,  or  Peyer's  patch,  in  a  state  of  distension  :  magnified  about  5 
diameters  (after  Boehm). 

in  diameter,  and,  according  to  the  degree  in  which  it  is  de- 
veloped, either  sunk  beneath,  or  more  or  less  prominently 
raised  on,  the  surface  of  a  depression  or  fossa  in  the  mucous 

FIG.  77. 


FIG.  76. — Solitary  gland  of  small  intestine  Rafter  Boehm). 

FIG.  77. — Part  of  a  patch  of  the  so-called  Peyer's  glands  magnified,  showing  the 
various  forms  of  the  sacculi,  with  their  zone  of  foramina.  The  rest  of  the  mem- 
brane marked  with  Lieberkuhn's  follicles,  and  sprinkled  with  villi  (after  Boehm). 


243 

membrane.  Each  gland  is  surrounded  by  openings  like  those 
of  Lieberkiihn's  follicles  (see  Fig.  77)  except  that  they  are 
more  elongated ;  and  the  direction  of  the  long  diameter  of 
each  opening  is  such  that  the  whole  produce  a  radiated  ap- 
pearance around  the  white  sacculus.  These  openings  appear 
to  belong  to  tubules  identical  with  Lieberkiihn's  follicles : 
they  have  no  communication  with  the  sacculus,  and  none  of 
its  contents  escape  through  them  on  pressure.  Neither  can 
any  permanent  opening  be  detected  in  the  sacculus  or  Peyer's 
gland  itself  (see  Fig.  78). 

Each  gland  is  an  imperfectly  closed  sac  or  follicle  formed 
of  a  tolerably  firm  membranous  capsule  of  fine  connective 
tissue,  imbedded  in  a  rich  plexus  of  minute  bloodvessels, 
many  fine  branches  from  which  pass  through  the  capsule  and 
enter,  chiefly  loopwise,  the  interior  of  the  follicle  (Fig.  79). 
Entering  into  the  formation  of  the  sacculus,  moreover,  and 
forming  a  stroma  or  supporting  framework  throughout  its  in- 
terior, is  lymphoid  or  adenoid  tissue  (Fig.  72),  continuous  with 
that  which  forms  a  great  part  of  the  mucous  membrane  out- 
side of  it.  The  contents  of  each  sac  consist  of  a  pale  grayish 


FIG.  78. 


a-  /,' 

Side  view  of  a  portion  of  intestinal  mucous  membrane  of  a  cat,  showing  a  Peyer's 
gland  (a) :  it  is  imbedded  in  the  submucous  tissue  (/),  the  line  of  separation  between 
which  and  the  mucous  membrane  passes  across  the  gland  ;  6,  one  of  the  tubular  fol- 
licles, the  orifices  of  which  form  the  zone  of  openings  around  the  gland  ;  c,  the  fossa 
in  the  mucous  membrane  ;  d,  villi ;  e,  follicles  of  Lieberkuhn  (after  Bendz). 

opalescent  pulp,  formed  of  albuminous  and  fatty  matter,  and 
a  multitude  of  nucleated  corpuscles  of  various  sizes,  resembling 
exactly  those  found  in  lymphatic  glands. 

The  real  office  of  these  Peyerian  glands  or  follicles  is  still 
unknown.     It  was  formerly  believed  that  each  follicle  was  a 


244 


DIGESTION. 


kind  of  secreting  cell,  which,  when  its  contents  were  fully  ma- 
tured, formed  a  communication  with  the  cavity  of  the  intes- 
tine by  the  absorption  or  bursting  of  its  own  cell -wall,  and  of 
the  portion  of  mucous  membrane  over  it,  and  thus  discharged 
its  secretion  into  the  intestinal  canal.  A  small  shallow  cavity 
or  space  was  thought  to  remain,  for  a  time,  after  this  absorp- 
tion or  dehiscence,  but  shortly  to  disappear,  together  with  all 
trace  of  the  previous  gland. 

More  recent  acquaintance  with  the  real  structure  of  these 
bodies  seems,  however,  to  prove  that  they  are  not  mere  tempo- 
rary gland-cells  which  thus  discharge  their  elaborated  con- 
tents into  the  intestine  and  then  disappear,  but  that  they  are 
rather  to  be  regarded  as  structures  analogous  to  lymphatic  or 


FIG.  79. 


Transverse  section  of  injected  Peyer's  glands  (from  Kolliker).  The  drawing  was 
taken  from  a  preparation  made  by  Frey :  it  represents  the  fine  capillary  looped  net- 
work spreading  from  the  surrounding  bloodvessels  into  the  interior  of  three  of 
Peyer's  capsules  from  the  intestine  of  the  rabbit. 

absorbent  glands,  and  that  their  office  is  to  take  up  certain 
materials  from  the  chyle,  elaborate  and  subsequently  discharge 
them  into  the  lacteals,  with  which  vessels  they  appear  to  be 
closely  connected,  although  no  direct  communication  has  been 
proved  to  exist  between  them. 

Moreover,  it  has  been  lately  suggested  that  since  the  mo- 


245^ 

lecular  and  cellular  contents  of  the  glands  are  so  abundantly 
traversed  by  minute  bloodvessels,  important  changes  may  mu- 
tually take  place  between  these  contents  and  the  blood  in  the 
vessels,  material  being  abstracted  from  the  latter,  elaborated 
by  the  cells,  and  then  restored  to  the  blood,  much  in  the  same 
manner  as  is  believed  to  be  the  case  in  the  so-called  vascular 
glands,  such  as  the  spleen,  thymus,  and  others ;  and  that  thus 
Peyer's  glands  should  also  be  regarded  as  closely  analogous  to 
these  vascular  glands.  Possibly  they  may  combine  the  func- 
tions both  of  lymphatic  and  vascular  glands,  absorbing  and 
elaborating  material  both  from  the  chyle  and  from  the  blood 
within  their  minute  vessels,  and  transmitting  part  to  the  lac- 
teal system  and  part  direct  to  the  blood. 

Brunrfs  glands  (Fig.  80)  are  confined  to  the  duodenum; 
they  are  most  abundant  and  thickly  set  at  the  commencement 

FIG.  80. 


Enlarged  view  of  one  of  Brunn's  glands  from  the  human  duodenum  (from  Frey). 
The  main  duct  is  seen  superiorly ;  its  branches  are  elsewhere  hidden  by  the  bunches 
of  opaque  glandular  vesicles. 

of  this  portion  of  the  intestine,  diminishing  gradually  as  the 
duodenum  advances.  Situated  beneath  the  mucous  membrane, 
and  imbedded  in  thesubmucous  tissue,  they  are  minutely  lobu- 
lated  bodies,  visible  to  the  naked  eye,  like  detached  small  por- 
tions of  pancreas,  and  provided  with  permanent  gland-ducts, 
which  pass  through  the  mucous  membrane  and  open  on  the 
internal  surface  of  the  intestine.  As  in  structure,  so  probably 
in  function,  they  resemble  the  pancreas;  or  at  least  stand  to  it 
in  a  similar  relation  to  that  which  the  small  labial  and  buccal 

21 


246 


DIGESTION. 


glands  occupy  in  relation  to  the  larger  salivary  glands,  the" 
parotid,  and  submaxillary. 

The  Villi  (Figs.  81,  82)  are  confined  exclusively  to  the  mu- 
cous membrane  of  the  small  intestine.  They  are  minute  vas- 
cular processes,  from  a  quarter  of  a  line  to  a  line  arid  two-thirds 
in  length,  covering  the  surface  of  the  mucous  membrane,  and 
giving  it  a  peculiar  velvety,  fleecy  appearance.  Krauss  esti- 


FIG.  81. 


(Slightly  altered  from  Teiehmann.)    A.  Villus  of  sheep.    B.  Villi  of  man. 

mates  them  at  fifty  to  ninety  in  number  in  a  square  line,  at 
the  upper  part  of  the  small  intestine,  and  at  forty  to  seventy 
in  the  same  area  at  the  lower  part.  They  vary  in  form  even 
in  the  same  animal,  and  differ  according  as  the  lymphatic  ves- 
sels they  contain  are  empty  or  full  of  chyle;  being  usually,  in 
the  former  case,  flat  and  pointed  at  their  summits,  in  the  latter 
cylindrical  or  clavate. 

Each  villus  consists  of  a  small  projection  of  mucous  mem- 
brane, and  its  interior  is  therefore  supported  throughout  by 


THE    VILLI. 


247 


fine  retiform  or  adenoid  tissue,  which  forms  the  framework  or 
stroma  in  which  the  other  constituents  are  contained. 

The  surface  of  the  villus  is  clothed  by  columnar  epithelium, 
which  rests  on  a  fine  basement-membrane;  while  within  this 


(From  Teichiminn.)  A,  lacteals  in  villi.  p,  Payer's  glands.  Band  D,  superficial 
and  deep  network  of  lacteals  in  sulmiucous  tissue.  L,  Lieberkiihn's  glands.  K,  small 
branch  of  lacteal  vessel  on  its  way  to  mesenteric  gland.  11  and  o,  muscular  fibres  of 
intestine,  s,  peritoneum. 

are  found,  reckoning  from  without  inwards,  bloodvessels,  fibres 
of  the  muscularu  mucosce,  and  a  single  lymphatic  or  lacteal 


248  DIGESTION. 

vessel  rarely  looped  or  branched  (Fig.  81);  besides  granular 
matter,  fat-globules,  &c. 

The  epithelium  is  of  the  columnar  kind,  and  continuous  with 
that  lining  the  other  parts  of  the  mucous  membrane.  The 
cells  are  arranged  with  their  long  axis  radiating  from  the  sur- 
face of  the  villus  (Fig.  81),  and  their  smaller  ends  resting  on 
the  basement-membrane.  Some  doubt  exists  concerning  the 
minute  structure  of  these  cells,  and  their  relation  to  the  deeper 
parts  of  the  villus. 

Beneath  the  basement  or  limiting  membrane  there  is  a  rich 
supply  of  bloodvessels.  Two  or  more  minute  arteries  are  dis- 
tributed within  each  villus ;  and  from  their  capillaries,  which 
form  a  dense  network,  proceed  one  or  two  small  veins,  which 
pass  out  at  the  base  of  the  villus. 

The  layer  of  the  muscularis  mucosce  in  the  villus  forms  a  kind 
of  thin  hollow  cone  immediately  around  the  central  lacteal, 
and,  is  therefore,  situate  beneath  the  bloodvessels.  The  ad- 
dition of  acetic  acid  to  the  villus  brings  out  the  characteristic 
nuclei  of  the  muscular  fibres,  and  shows  the  size  and  position 
of  the  layer  most  distinctly.  Its  use  is  still  unknown,  although 
it  is  impossible  to  resist  the  belief,  that  it  is  instrumental  in  the 
propulsion  of  chyle  along  the  lacteal. 

The  lacteal  vessel  enters  the  base  of  each  villus,  and  passing 
up  in  the  middle  of  it,  extends  nearly  to  the  tip,  where  it  ends 
commonly  by  a  closed  and  somewhat  dilated  extremity.  In 
the  larger  villi  there  may  be  two  small  lacteal  vessels  which 
end  by  a  loop  (Fig.  81.),  or  the  lacteals  may  form  a  kind  of 
network  in  the  villus.  The  last  method  of  ending,  however, 
is  rarely  or  never  seen  in  the  human  subject,  although  com- 
mon in  some  of  the  lower  animals  (A,  Fig.  81). 

The  office  of  the  villi  is  the  absorption  of  chyle  from  the 
completely  digested  food  in  the  intestine.  The  mode  in  which 
they  effect  this  will  be  considered  in  the  chapter  on  Absorp- 
tion. 

Structure  of  the  Large  Intestine. 

The  large  intestine,  which  in  an  adult  is  from  about  4  to 
6  feet  long,  is  subdivided  for  descriptive  purposes  into  three 
portions,  viz. :  the  ccecum,  a  short  wide  pouch,  communicating 
with  the  lower  end  of  the  small  intestine  through  an  opening, 
guarded  by  the  ileo-ccecal  valve  ;  the  colon,  continuous  with  the 
caecum,  which  forms  the  principal  part  of  the  large  intestine, 
and  is  divided  into  an  ascending,  transverse,  and  descending 
portion  ;  and  the  rectum,  which,  after  dilating  at  its  lower  part, 
again  contracts,  and  immediately  afterwards  opens  externally 


THE    LARGE    IXTESTIXE.  249 

through  the  anus.  Attached  to  the  caecum  is  the  small  appen- 
dix vermiformis. 

Like  the  small  intestine,  the  large  is  constructed  of  three 
principal  coats,  viz.,  the  serous,  muscular,  and  mucous.  The 
serous  coat  need  not  be  here  particularly  described.  Connected 
with  it  are  the  small  processes  of  peritoneum  containing  fat, 
called  appendices  epiploicce.  The  fibres  of  the  muscular  coat, 
like  those  of  the  small  intestine,  are  arranged  in  two  layers — 
the  outer  longitudinally,  the  inner  circularly.  In  the  caecum 
and  colon,  the  longitudinal  fibres,  besides  being,  as  in  the  small 
intestine,  thinly  disposed  in  all  parts  of  the  wall  of  the  bowel, 
are  collected,  for  the  most  part,  into  three  strong  bands,  which 
being  shorter,  from  end  to  end,  than  the  other  coats  of  the  in- 
testine, hold  the  canal  in  folds,  bounding  intermediate  sacculi. 
On  the  division  of  these  bands,  the  intestine  can  be  drawn  out 
to  its  full  length,  and  it  then  assumes,  of  course,  a  uniformly 
cylindrical  form.  In  the  rectum,  the  fasciculi  of  these  longi- 
tudinal bands  spread  out  and  mingle  with  the  other  longitudi- 
nal fibres,  forming  with  them  a  thicker  layer  of  fibres  than 
exists  on  any  other  part  of  the  intestinal  canal.  The  circular 
muscular  fibres  are  spread  over  the  whole  surface  of  the  bowel, 
but  are  somewhat  more  marked  in  the  intervals  between  the 
sacculi.  Towards  the  lower  end  of  the  rectum  they  become 
more  numerous,  and  at  the  anus  they  form  a  strong  band  called 
the  internal  sphincter  muscle. 

The  mucous  membrane  of  the  large,  like  that  of  the  small 
intestine,  is  lined  throughout  by  columnar  epithelium,  but, 
unlike  it,  is  quite  smooth  and  destitute  of  villi,  and  is  not  pro- 
jected in  the  form  of  valvulse  conniveutes.  Its  general  micro- 
scopic structure  resembles  that  of  the  small  intestine. 

Glands  of  the  Large  Intestine. — The  glands  with  which  the 
large  intestine  is  provided  are  of  two  kinds,  the  tubular  and. 
lenticular. 

The  tubular  glands,  or  glands  of  Lieberkiihn,  resemble  those 
of  the  small  intestine,  but  are  somewhat  larger  and  more 
numerous.  They  are  also  more  uniformly  distributed. 

The  lenticular  glands  are  most  numerous  in  the  caecum  and 
vermiform  appendix.  They  resemble  in  shape  and  structure, 
almost  exactly,  the  solitary  glands  of  the  small  intestine,  and, 
like  them,  have  no  opening.  Just  over  them,  however,  there 
is  commonly  a  small  depression  in  the  mucous  membrane, 
which  has  led  to  the  erroneous  belief  that  some  of  them  open 
on  the  surface. 

The  functions  discharged  by  the  glands  found  in  the  large 
intestine  are  not  known  with  any  certainty,  but  there  is  no 


250  DIGESTION. 

reason  to  doubt  that  they  resemble  very  nearly  those  discharged 
by  the  glands  of  like  structure  in  the  small  intestine. 

The  difficulty  of  determining  the  function  of  any  single  set 
of  the  intestinal  glands  seems  indeed  almost  insuperable,  so 
many  fluids  being  discharged  together  into  the  intestine ;  for 
all  acting,  probably,  at  once,  produce  a  combined  effect  upon 
the  food,  so  that  it  is  almost  impossible  to  discern  the  share  of 
any  one  of  them  in  digestion. 

Ileo-ccecal  valve. — The  ileo-csecal  valve  is  situate  at  the  place 
of  junction  of  the  small  with  the  large  intestine,  and  guards 
against  any  reflux  of  the  contents  of  the  latter  into  the  ileum. 
It  is  composed  of  two  semilunar  folds  of  mucous  membrane. 
Each  fold  is  formed  by  a  doubling  inwards  of  the  mucous  mem- 
brane, and  is  strengthened  on  the  outside  by  some  of  the  circu- 
lar muscular  fibres  of  the  intestine,  which  are  contained  be- 
tween the  outer  surfaces  of  the  two  layers  of  which  each  fold 
is  composed.  The  inner  surface  of  the  folds  is  smooth ;  the 
mucous  membrane  of  the  ileum  being  continuous  with  that  of 
the  csecum.  That  surface  of  each  fold  which  looks  towards  the 
small  intestine  is  covered  with  villi,  while  that  which  looks  to 
the  csecum  has  none.  When  the  csecum  is  distended,  the 
margins  of  the  folds  are  stretched,  and  thus  are  brought  into 
firm  apposition  one  with  the  other. 

While  the  circular  muscular  fibres  of  the  bowel  at  the  junc- 
tion of  the  ileum  with  the  csecum  are  contained  between  the 
outer  opposed  surfaces  of  the  folds  of  mucous  membrane  which 
form  the  valve,  the  longitudinal  muscular  fibres  and  the  peri- 
toneum of  the  small  and  large  intestine  respectively  are  con- 
tinuous with  each  other,  without  dipping  in  to  follow  the  cir- 
cular fibres  and  the  mucous  membrane.  In  this  manner, 
therefore,  the  folding  inwards  of  these  two  last-named  structures 
is  preserved,  while  on  the  other  hand,  .by  dividing  the  longi- 
tudinal muscular  fibres  and  the  peritoneum,  the  valve  can  be 
made  to  disappear,  just  as  the  constrictions  between  the  sacculi 
of  the  large  intestine  can  be  made  to  disappear  by  performing 
a  similar  operation. 

The  Pancreas,  and  its  Secretion. 

The  pancreas  is  situated  within  the  curve  formed  by  the 
duodenum ;  ami  its  main  duct  opens  into  that  part  of  the  in- 
testine, either  through  a  small  opening  or  through  a  duct  com- 
mon to  itself  and  to  the  liver.  The  pancreas,  in  its  minute 
anatomy,  closely  resembles  the  salivary  glands ;  and  the  fluid 
elaborated  by  it  appears  almost  identical  with  saliva.  When 
obtained  pure,  in  all  the  different  animals  in  which  it  has  been 


THE    PA  Is  CREATIC    SECRETION.  251 

hitherto  examined,  it  has  been  found  colorless,  transparent,  and 
slightly  viscid.  It  is  alkaline  when  fresh,  and  contains  a  pecu- 
liar animal  matter  named  pancreatin  and  certain  salts,  both  of 
which  are  very  similar  to  those  found  in  saliva.  In  pancreatic 
secretion,  however,  there  is  no  sulpho-cyanogen.  Pancreatin 
is  a  substance  coagulable  by  heat,  and  in  many  other  respects 
very  like  albumen :  to  it  the  peculiar  digestive  power  of  the 
pancreatic  secretion  is  probably  due-.  Like  saliva,  the  pan- 
creatic fluid,  shortly  after  its  escape,  becomes  neutral  and 
then  acid. 

The  following  is  the  mean  of  three  analyses  by  Schmidt : 

Composition  of  Pancreatic  Secretion. 

Water, 980.45 

Solids, 19.55 

Panerealin,      .  .         .     •     .         .         .1271 

Inorganic  bases  and  salt?,        .         .         .         .         6  84 

19.55 

The  functions  of  the  pancreas  are  probably  as  follows : 

1.  Numerous  experiments  have  shown,  that  starch  is  acted 
upon  by  the  pancreatic  secretion,  or  by  portions  of  pancreas 
put  in  starch-paste,  in  the  same  manner  that  it  is  by  saliva  and 
portions  of  the  salivary  glands.      And  although,  as  before 
stated  (p.  212),  many  substances  besides  those  glands  can  ex- 
cite the  transformation  of  starch  into  dextrin  and  grape-sugar, 
yet  it  appears  probable  that  the  pancreatic  fluid,  exercising 
this  power  of  transformation,  is  largely  subservient  to  the  pur- 
pose of  digesting  starch.     MM.  Bouchardat  and  Sandras  have 
shown  that  the  raw  starch-granules  which   have  passed  un- 
changed through  the  crops  and  gizzards  of  granivorous  birds, 
or  through  the  stomachs  of  herbivorous  Mammalia,  are,  in  the 
small  intestine,  disorganized,  eroded,  and  finally  dissolved,  as 
they  are  when  exposed,  in  experiment,  to  the  action  of  the 
pancreatic  fluid.      The  bile  cannot  effect  such  a  change  m 
starch ;  and  it  is  most  probable  that  the  pancreatic  secretion  is 
the  principal  agent  in  the  transformation,  though  it  is  by  no 
means  clear  that  the  office  may  not  be  shared  by  the  secretion 
of  the  intestinal  mucous  membrane,  whicli  alsf>  seems  to  possess 
the  power  of  converting  starch  into  sugar. 

2.  The  existence  of  a  pancreas   in   Carnivora,  which  have 
little  or  no  starch  in  their  food,  and  the  results  of  various  ob- 
servations and   experiments,  leave  very  little  doubt  that  the 
pancreatic  secretion  also  assists  largely  in    the  digestion  of 


252  DIGESTION. 

fatty  matters,  by  transforming  them  into  a  kind  of  emulsion, 
and  thus  rendering  them  capable  of  absorption  by  the  lacteals. 
Several  cases  have  been  recorded  in  which  the  pancreatic  duct 
being  obstructed,  so  that  the  secretion  could  not  be  discharged, 
fatty  or  oily  matter  was  abundantly  discharged  from  the  in- 
testines. In  nearly  all  these  cases,  indeed,  the  liver  was  eoin- 
cidently  diseased,  and  the  change  or  absence  of  the  bile  might 
appear  to  contribute  to  the  result ;  yet  the  frequency  of  exten- 
sive disease  of  the  liver,  unaccompanied  by  fatty  discharges 
from  the  intestines,  favors  the  view  that,  in  these  cases,  it  is  to 
the  absence  of  the  pancreatic  fluid  from  the  intestines  that  the 
excretion  or  non-absorption  of  fatty  matter  should  be  ascribed. 
In  Bernard's  experiments  too,  fat  always  appeared  in  the 
evacuations  when  the  pancreas  was  destroyed  or  its  duct  tied. 
Bernard,  indeed,  is  of  opinion  that  to  emulsify  fat  is  the  ex- 
press office  of  the  pancreas,  and  the  evidence  that  he  and 
others  have  brought  forward  in  support  of  this  view  is  very 
weighty.  The  power  of  emulsifying  fat,  however,  although 
perhaps  mainly  exercised  by  the  secretion  of  the  pancreas,  is 
evidently  possessed  to  some  extent  by  other  secretions  poured 
into  the  intestines,  and  especially  by  the  bile. 

3.  The  pancreatic  secretion  discharges  a  third  function  also, 
namely,  that  of  dissolving  albuminous  substances  ;  the  peptone 
produced  by  the  action  of  the  pancreatic  secretion  on  proteids 
not  differing  essentially  from  that  formed  by  the  action  of  the 
gastric  juice  (see  p.  229). 


Structure  of  the  Liver. 

The  liver  is  an  extremely  vascular  organ,  and  receives  its 
supply  of  blood  from  two  distinct  vessels,  the  portal  vein  and 
hepatic  artery,  while  the  blood  is  returned  from  it  into  the 
vena  cava  inferior  by  the  hepatic  vein.  Its  secretion,  the  bile, 
is  conveyed  from  it  by  the  hepatic  duct,  either  directly  into  the 
intestine,  or,  when  digestion  is  not  going  on,  into  the  cystic 
duct,  and  thence  into  the  gall-bladder,  where  it  accumulates 
until  required.  The  portal  vein,  hepatic  artery,  and  hepatic 
duct  branch  together  throughout  the  liver,  while  the  hepatic 
vein  and  its  tributaries  run  by  themselves. 

On  the  outside  the  liver  has  an  incomplete  covering  of  peri- 
toneum, and  beneath  this  is  a  very  fine  coat  of  areolar  tissue, 
continuous  over  the  whole  surface  of  the  organ.  It  is  thickest 
where  the  peritoneum  is  absent,  and  is  continuous  on  the 
general  surface  of  the  liver  with  the  fine,  and,  in  the  human 
subject,  almost  imperceptible,  areolar  tissue  investing  the 


STRUCTURE     OF    THE     LIVER. 


253 


lobules.     At  the  transverse  fissure  it  is  merged  in  the  areolar 
investment  called  Glisson's  capsule,  which  surrounding    the 


FIG.  83. 


Under  surface  of  the  liver  (from  Bonamy). 

R,  right  lobe ;  L,  left  lobe ;  Q.  lobus  quadratus  ;  S,  lobus  Spigelii ;  C,  lobus  caudatus ; 
1,  umbilical  vein  in  longitudinal  fissure;  2,  gall-bladder  in  its  fissure;  8,  hepatic  ar- 
tery in  transverse  fissure ;  4,  hepatic  duct  in  transverse  fissure ;  5,  portal  vein  in 
transverse  fissure;  6,  line  of  reflexion  of  peritoneum;  7,  vena  cava;  8,  obliterated 
ductus  venosus  ;  9,  ductus  commuuis  choledochus. 


FIG.  84. 


portal  vein,  hepatic  artery,  and  hepatic  duct,  as  they  enter  at 
this    part,    accompanies   them   in 
their  branchings  through  the  sub- 
stance of  the  liver. 

The  liver  is  made  up  of  small 
roundish  or  oval  portions  called 
lobules,  each  of  which  is  about  ^ 
of  an  inch  in  diameter,  and  com- 
posed of  the  minute  branches  of 
the  portal  vein,  hepatic  artery,  he- 
patic duct,  and  hepatic  vein  ;  while 
the  interstices  of  these  vessels  are 
filled  by  the  liver  cells.  These  cells  (Fig.  84),  which  make 
up  a  great  portion  of  the  substance  of  the  organ,  are  rounded 
or  polygonal,  from  about  g^0  to  j^  of  an  inch  in  diameter, 
containing  well-marked  nuclei  and  granules,  and  having 
sometimes  a  yellowish  tinge,  especially  about  their  nuclei ;  fre- 
quently, they  contain  also  various  sized  particles  of  fat  (Fig. 
84  A).  Each  lobule  is  very  sparingly  invested  by  areolar  tis- 
sue. 

To  understand  the  distribution  of  the  bloodvessels  in  the 

22 


254  DIGESTION. 

liver,  it  will  be  well  to  trace,  first,  the  two  bloodvessels  and 
the  duct  which  enter  the  organ  on  the  under  surface  at  the 
transverse  fissure,  viz.,  the  portal  vein,  hepatic  artery,  and  he- 
patic duct.  As  before  remarked,  all  three  run  in  company, 
and  their  appearance  on  longitudinal  section  is  shown  in  Fig. 
85.  Running  together  through  the  substance  of  the  liver, 

FIG.  85. 


Longitudinal  section  of  a  portal  canal,  containing  a  portal  vein,  hepatic  artery, 
and  hepatic  duct,  from  the  pig  (after  Kiernan)  ^.  p,  branch  of  vena  portse,  situated 
in  a  portal  canal,  formed  amongst  the  lobules  of  the  liver,  and  giving  off  vaginal 
branches;  there  are  also  seen  within  the  large  portal  vein  numerous  orifices  of  the 
smallest  interlobular  veins  arising  directly  from  it ;  A,  hepatic  artery  ;  D,  hepatic 
duct. 

they  are  contained  in  small  channels,  called  portal  canals,  their 
immediate  investment  being  a  sheath  of  areolar  tissue,  called 
Glisson's  capsule. 

To  take  the  distribution  of  the  portal  vein  first:  In  its  course 
through  the  liver  this  vessel  gives  off  small  branches,  which 
divide  and  subdivide  between  the  lobules  surrounding  them 
and  limiting  them,  and  from  this  circumstance  called  inter- 
lobular  veins;  From  these  small  vessels  a  dense  capillary  net- 
work is  prolonged  into  the  substance  of  the  lobule,  and  this 
network  gradually  gathering  itself  up,  so  to  speak,  into  larger 
vessels,  converges  finally  to  a  single  small  vein,  occupying  the 
centre  of  the  lobule,  and  hence  called  wJralobular.  This  ar- 


STRUCTURE    OF    THE    LIVER.  255 

rangement  is  well  seen  in  Fig.  86,  which  represents  a  trans- 
verse section  of  a  lobule.  The  smaller  branches  of  the  portal 
vein  being  closely  surrounded  by  the  lobules,  give  off  directly 


FIG.  86. 


Cross-section  of  a  lobule  of  the  human  liver,  in  which  the  capillary  network  be- 
tween the  portal  and  hepatic  veins  has  been  fully  injected  (from  Sappey)  60  j. 
Section  of  the  iw/ralobular  vein;  2,  its  smaller  branches  collecting  blood  from  the 
capillary  network  ;  3,  tnterlobular  branches  of  the  vena  portse  with  their  smaller 
ramifications  passing  inwards  towards  the  capillary  network  in  the  substance  of 
the  lobule. 


veins  (see  Fig.  85)  ;  but  here  and  there,  especially 
where  the  hepatic  artery  and  duct  intervene,  branches  called 
vaginal  first  arise,  and  breaking  up  in  the  sheath  are  subse- 
quently distributed  like  the  others  around  the  lobules  and  be- 
come mferlobular.  The  larger  trunks  of  the  portal  vein  being 
more  separated  from  the  lobules  by  a  thicker  sheath  of  Glisson's 
capsule,  give  off  vaginal  branches  alone,  which,  however,  after 
breaking  up  in  the  sheath,  are  distributed  like  the  others  be- 
tween the  lobules,  and  become  iwferlobular  veins. 

The  small  m£ralobular  veins  discharge  their  contents  into 
veins  called  sitMobular  (Fig.  88),  while  these  again,  by  their 
union,  form  the  main  branches  of  the  hepatic  vein,  which  leaves 
the  posterior  border  of  the  liver  to  end  by  two  or  three  prin- 
cipal trunks  in  the  inferior  vena  cava,  just  before  its  passage 
through  the  diaphragm.  The  s-u61obular  and  hepatic  veins, 
unlike  the  portal  vein  and  its  companions,  have  little  or  no 
areolar  tissue  around  them,  and  their  coats  being  very  thin, 


256  DIGESTION. 

they  form  little  more  thaD  mere  channels  in  the  liver  sub- 
stance which  closely  surrounds  them. 


FIG.  87. 


Section  of  a  portion  of  liver  passing  longitudinally  through  a  considerable  hepatic 
vein,  from  the  pig  (after  Kiernan)  5..  H,  hepatic  venous  trunk,  against  which  the 
sides  of  the  lobules  are  applied ;  b,  sublobular  hepatic  veins,  on  which  the  bases  of 
the  lobules  rest,  and  through  the  coats  of  which  they  are  seen  as  polygonal  figures  ; 
a,  a,  walls  of  the  hepatic  venous  canal,  formed  by  the  polygonal  bases  of  the  lobules. 

The  manner  in  which  the  lobules  are  connected  with  the 
sublobular  veins  by  means  of  the  small  intralobular  veins  is 
well  seen  in  the  diagram,  Fig.  88,  and  in  Fig.  87,  which  rep- 
resent the  parts  as  seen  in  a  longitudinal  section.  The  ap- 
pearance has  been  likened  to  a  twig  having  leaves  without 
footstalks — the  lobules  representing  the  leaves,  and  the  sub- 
lobular vein  the  small  branch  from  which  it  springs.  On  a 
transverse  section,  the  appearance  of  the  intralobular  veins  is 
that  of  1,  Fig.  86,  while  both  a  transverse  and  longitudinal 
section  are  exhibited  in  Fig.  89. 

The  hepatic  artery,  the  function  of  which  is  to  distribute 
blood  for  nutrition  to  Glisson's  capsule,  the  walls  of  the  ducts 
and  bloodvessels,  and  other  parts  of  the  liver,  is  distributed  in 
a  very  similar  manner  to  the  portal  vein,  its  blood  being  re- 
turned by  small  branches  either  into  the  ramifications  of  the 


STRUCTURE    OF    THE    LIVER. 


257 


FIG.  88. 


Lobu.Ii 


portal  vein,  or  into  the  capillary  plexus  of  the  lobules  which 
connects  the  inter-  and  mfralobular  veins. 

The  hepatic  duct  divides  and  subdivides  in  a  manner  very 
like  that  of  the  portal  vein  and 
hepatic  artery,  the  larger  branches 
being  lined  by  cylindrical,  and  the 
smaller  by  small  polygonal  epi- 
thelium. The  exact  arrangement 
of  its  terminal  branches,  however, 
and  their  relation  to  the  liver-cells 
have  not  been  clearly  made  out,  or, 
at  least,  have  not  been  agreed  upon 
by  different  observers.  The  chief 
theories  on  the  subject  are  three  in 
number: 

1.  That  the  terminal  branches 

of  the  hepatic  duct  form  an  inter-    Loin 
lobular  network,  which   abuts  on 
the  outermost  cells  of  a  lobule,  but 
does  not  enter  the  inside  of  the  lob- 
ule, or  only  for  a  little  way. 

2.  That  minute  branches  begin  on  the  sublobular  veins  (after  Kier- 
in  the  lobules  between  the  cells,  not  nan). 

inclosing  them. 

3.  That  the  ultimate  branches  begin  in  the  lobules  and  in- 
close hepatic  cells. 

FIG.  89. 


Diagram  showing  the  manner  in 
which  the  lobules  of  the  liver  rest 


Capillary  network  of  the  lobules  of  the  rabbit's  liver  (from  Kolliker)  4T5.  The 
figure  is  taken  from  a  very  successful  injection  of  the  hepatic  veins,  made  by  Hart- 
ing:  it  shows  nearly  the  whole  of  two  lobules,  and  parts  of  three  others;  p,  portal 
branches  running  in  the  interlobular  spaces;  h,  hepatic  veins  penetrating  and  radi- 
ating from  the  centre  of  the  lobules. 


258 


DIGESTION. 


The  illustrations  below  will  show  the  conflicting  theories  at 
a  glance. 


FIG.  90. 


Diagrams  showing  the  arrangement  of  the  radicles  of  the  hepatic  duct,  according 
to  different  observers. 

1.  2,  2,  are  two  branches  of  the  hepatic  duct,  which  is  supposed  to  commence  in  a 
plexus  situated  towards  the  circumference  of  the  lobule  marked  4,  4,  called  by  Kier- 
nan  the  biliary  plexus.    Within  this  is  seen  the  central  part  of  the  lobule,  contain- 
ing- branches  of  the  intralobular  vein,  1,  1. 

2.  A  small  fragment  of  an  hepatic  lobule,  of  which  the  smallest  intercellular  bili- 
ary ducts  were  filled  with  coloring  matter  during  life,  highly   magnified   (from 
Chrzonszczewsky). 

3.  View  of  some  of  the  smallest  biliary  ducts  illustrating  Beale's  view  of  their 
relation  to  the  biliary  cells  (from  Kolliker  after  Beale),  1  |A. 

The  drawing  is  taken  from  an  injected  preparation  of  the  pig's  liver  ;  a,  small 
branch  of  an  interlobular  hepatic  duct ;  c,  smallest  biliary  ducts  ;  b,  portions  of  the 
cellular  part  of  the  lobule  in  which  the  cells  are  seen  within  tubes  which  commu- 
nicate with  the  finest  ducts. 


THE     BILE.  259 

Functions  of  the  Liver. 

The  Secretion  of  Bile  is  the  most  obvious,  and  one  of  the 
chief  functions  which  the  liver  has  to  perform ;  but,  as  will  be 
presently  shown,  it  is  not  the  only  one ;  for  important  changes 
are  effected  in  certain  constituents  of  the  blood  in  its  transit 
through  this  gland,  whereby  they  are  rendered  more  fit  for 
their  subsequent  purposes  in  the  animal  economy. 

The  Bile. 

Composition  of  the  Bile. — The  bile  is  a  somewhat  viscid  fluid, 
of  a  yellow  or  greenish-yellow  color,  a  strongly  bitter  taste, 
and  when  fresh  with  a  scarcely  perceptible  odor ;  it  has  a 
neutral  or  slightly  alkaline  reaction,  and  its  specific  gravity  is 
about  1020.  Its  color  and  degree  of  consistence  vary  much, 
apparently  independent  of  disease  ;  but,  as  a  rule,  it  becomes 
gradually  more  deeply  colored  and  thicker  as  it  advances 
along  its  ducts,  or  when  it  remains  long  in  the  gall-bladder, 
wherein,  at  the  same  time,  it  becomes  more  viscid  and  ropy, 
of  a  darker  color,  and  more  bitter  taste,  mainly  from  its 
greater  degree  of  concentration,  on  account  of  partial  absorp- 
tion of  its  water,  but  partly  also  from  being  mixed  with  mucus. 

The  following  analysis  is  by  Frerichs : 

Composition  of  Human  Bile. 

Water, 859.2 

Solids, 140.8 

1000.0 

Biliary  acids  combined  "I    D.r  nl  K 

with  alkalies,  }   Bllin'     •         •         •         •     *™ 

Fat, 9.2 

Cholesterin, 2.6 

Mucus  and  coloring  matters,           ....     29.8 
Salts, 7.7 

140.S 

The  bilin  or  biliary  matter  when  freed  by  ether  from  the  fat 
with  which  it  is  combined,  is  a  resinoid  substance,  soluble  in 
water,  alcohol,  and  alkaline  solutions,  and  giving  to  the  watery 
solution  the  taste  and  general  character  of  bile.  It  is  a  com- 
pound of  soda,  with  two  resinous  acids,  named  glycocholic 
and  taurocholic  acids.  The -former  consists  of  cholic  acid 
conjugated  with  glycin  (or  sugar  of  gelatin),  the  latter  of  the 
same  acid  conjugated  with  taurin. 

Fatty  substances  are  found  in  variable  proportions.     Besides 


260 


DIGESTION. 


FIG.  91. 


Crystalline  scales  of  c-holcsterin. 


the  ordinary  saponifiable  fats,  there  is  a  small  quantity  of 
cholesterin  (p.  20),  which,  with  the  other  free  fats,  is  probably 
held  in  solution  by  the  tauro-cholate  of  soda. 

A  peculiar  substance,  which  Dr.  Flint  has  discovered  in  the 
faeces,  and  named  stercorin  (p.  274),  is  closely  allied  to  choles- 
terin ;  and  Dr.  Flint  believes 
that  while  one  great  function  of 
the  liver  is  to  excrete  cholesterin 
from  the  blood,  as  the  kidney 
excretes  urea,  the  stercorin  of 
fseces  is  the  modified  form  in 
which  cholesterin  finally  leaves 
the  body.  Ten  grains  and  a 
half  of  stercorin,  he  reckons,  are 
excreted  daily. 

The  coloring  matter  of  the  bile 
has  not  yet  been  obtained  pure, 
owing  to  the  facility  with  which 
it  is  decomposed.  It  occasionally 
deposits  itself  in  the  gall-bladder 
as  a  yellow  substance  mixed  with 

mucus,  and  in  this  state  has  been  frequently  examined.  It 
is  composed  of  two  coloring  matters,  called  biliverdin  and 
bilifalvin.  By  oxidizing  agencies,  as  exposure  to  the  air,  or 
the  addition  of  nitric  acid,  it  assumes  a  dark  green  color.  In 
cases  of  biliary  obstruction,  it  is  often  reabsorbed,  circulates 
with  the  blood,  and  gives  to  the  tissues  the  yellow  tint  charac- 
teristic of  jaundice. 

There  seems  to  be  some  relationship  between  the  coloring 
matters  of  the  blood  and  bile,  and,  it  may  be  added,  between 
these  and  that  of  the  urine  also,  so  that  it  is  possible  they  may 
be,  all  of  them,  varieties  of  the  same  pigment,  or  derived  from 
the  same  source.  Nothing,  however,  is  at  present  certainly 
known  regarding  the  relation  in  which  one  of  them  stands  to 
the  other. 

The  mucus  in  bile  is  derived  chiefly  from  the  mucous  mem- 
brane of  the  gall-bladder,  but  in  part  also  from  the  hepatic 
ducts  and  their  branches.  It  constitutes  the  residue  after  bile 
is  treated  with  alcohol.  The  epithelium  with  which  it  is 
mixed  may  be  detected  in  the  bile  with  the  microscope  in  the 
form  of  cylindrical  cells,  either  scattered  or  still  held  together 
in  layers.  To  the  presence  of  this  mucus  is  probably  to  be 
ascribed  the  rapid  decomposition  undergone  by  the  bilin  ;  for, 
according  to  Berzelius,  if  the  mucus  be  separated,  bile  will 
remain  unchanged  for  many  days. 

The  saline  or  inorganic  constituents  of  the  bile  are  similar  to 


THE    BILE.  261 

those  found  in  most  other  secreted  fluids.  It  is  possible  that 
the  carbonate  and  neutral  phosphate  of  sodium  and  potassium, 
found  in  the  ashes  of  bile,  are  formed  in  the  incineration,  and 
do  not  exist  as  such  in  the  fluid.  Oxide  of  iron  is  said  to  be 
a  common  constituent  of  the  ashes  of  bile,  and  copper  is  gen- 
erally found  in  healthy  bile,  and  constantly  in  biliary  calculi. 

Such  are  the  principal  chemical  constituents  of  bile ;  but  its 
physiology  is,  perhaps,  better  illustrated  by  its  ultimate  ele- 
mentary composition.  According  to  Liebig's  analysis,  the 
biliary  matter, — consisting  of  bilin  and  the  products  of  its 
spontaneous  decomposition — yields,  on  analysis,  76  atoms  of 
carbon,  66  of  hydrogen,  22  of  oxygen,  2  of  nitrogen,  and  a  cer- 
tain quantity  of  sulphur.1  Comparing  this  with  the  ultimate 
composition  of  the  organic  parts  of  blood,  which  may  be  stated 
at  C4SH36N6O14,  with  sulphur  and  phosphorus — it  is  evident  that 
bile  contains  a  large  preponderance  of  carbon  and  hydrogen, 
and  a  deficiency  of  nitrogen.  The  import  of  this  will  pres- 
ently appear. 

TESTS  FOR  BILE. — A  common  test  for  the  presence  of  bile 
consists  of  the  addition  of  a  small  quantity  of  nitric  acid,  when, 
if  bile  be  present,  a  play  of  colors  is  produced,  beginning  with 
green  and  passing  through  various  tints  to  red.  This  test  will 
detect  only  the  coloring  matter  of  the  bile. 

The  best  test  for  the  bilin  is  Pettenkofer's.  To  the  liquid 
suspected  to  contain  bile  must  be  added,  first,  a  drop  or  two  of 
a  strong  solution  of  cane-sugar  (one  part  of  sugar  to  four  parts 
of  water),  and  immediately  afterwards  sulphuric  acid,  to  the 
extent  of  about  two-thirds  of  the  liquid.  On  first  adding  the 
acid,  a  whitish  precipitate  falls;  but  this  redissolves  with  a 
slight  excess  of  the  acid,  and  on  the  further  addition  of  the 
latter  there  appears  a  bright  cherry-red  color,  gradually  chang- 
ing through  a  lake  tint  to  a  dark  purple. 

The  process  of  secreting  bile  is  probably  continually  going 
on,  but  appears  to  be  retarded  during  fasting,  and  accelerated 
on  taking  food.  This  was  shown  by  Blondlot,  who,  having 
tied  the  common  bile-duct  of  a  dog,  and  established  a  fistulous 
opening  between  the  skin  and  gall-bladder,  whereby  all  the  bile 
secreted  was  discharged  at  the  surface,  noticed  that  when  the 
animal  was  fasting,  sometimes  not  a  drop  of  bile  was  discharged 
for  several  hours ;  but  that,  in  about  ten  minutes  after  the 


1  The  sulphur  is  combined  with  the  taurin — one  of  the  substances 
yielded  by  the  decomposition  of  bilin.  According  to  Dr.  Kemp,  the 
sulphur  in  the  bile  of  the  ox,  dried  and  freed  from  mucus,  coloring 
matter,  and  salts,  constitutes  about  3  per  cent. 


262  DIGESTION. 

introduction  of  food  into  the  stomach,  the  bile  began  to  flow 
abundantly,  and  continued  to  do  so  during  the  whole  period 
of  digestion.  Bidder  and  Schmidt's  observations  are  quite  in 
accordance  with  this. 

The  bile  is  probably  formed  first  in  the  hepatic  cells ;  then, 
being  discharged  into  the  minute  hepatic  ducts,  it  passes  into 
the  larger  trunks,  and  from  the  main  hepatic  duct  may  be 
carried  at  once  into  the  duodenum.  But,  probably,  this  hap- 
pens only  while  digestion  is  going  on ;  during  fasting  it  flows 
from  the  common  bile-duct  into  the  cystic-duct,  and  thence 
into  the  gall-bladder,  where  it  accumulates  till,  in  the  next 
period  of  digestion,  it  is  discharged  into  the  intestine.  The 
gall-bladder  thus  fulfils  what  appears  to  be  its  chief  or  only 
office,  that  of  a  reservoir ;  for  its  presence  enables  bile  to  be 
constantly  secreted  for  the  purification  of  the  blood,  yet  insures 
that  it  shall  all  be  employed  in  the  service  of  digestion,  although 
digestion  is  periodic,  and  the  secretion  of  bile  constant. 

The  mechanism  by  which  the  bile  passes  into  the  gall-bladder 
is  simple.  The  orifice  through  which  the  common  bile-duct 
communicates  with  the  duodenum  is  narrower  than  the  duct, 
and  appears  to  be  closed,  except  when  there  is  sufficient  pres- 
sure behind  to  force  the  bile  through  it.  The  pressure  exer- 
cised upon  the  bile  secreted  during  the  intervals  of  digestion 
appears  insufficient  to  overcome  the  force  with  which  the  orifice 
of  the  duct  is  closed  ;  and  the  bile  in  the  common  duct,  finding 
no  exit  in  the  intestine,  traverses  the  cystic-duct,  and  so  passes 
into  the  gall-bladder,  being  probably  aided  in  this  retrograde 
course  by  the  peristaltic  action  of  the  ducts.  The  bile  is  dis- 
charged from  the  gall-bladder,  and  enters  the  duodenum  on 
the  introduction  of  food  into  the  small  intestine  :  being  pressed 
on  by  the  contraction  of  the  coats  of  the  gall-bladder,  and 
probably  of  the  common  bile-duct  also ;  for  both  these  organs 
contain  organic  muscular  fibre-cells.  Their  contraction  is  ex- 
cited by  the  stimulus  of  the  food  in  the  duodenum  acting  so  as 
to  produce  a  reflex  movement,  the  force  of  which  is  sufficient 
to  open  the  orifice  of  the  common  bile-duct. 

Various  estimates  have  been  made  of  the  quantity  of  bile  dis- 
charged in  the  intestines  in  twenty-four  hours :  the  quantity 
doubtless  varying,  like  that  of  the  gastric  fluid,  in  proportion 
to  the  amount  of  food  taken.  A  fair  average  of  several  com- 
putations would  give  thirty  to  forty  ounces  as  the  quantity 
daily  secreted  by  man. 

The  purposes  served  by  the  secretion  of  bile  may  be  considered 
to  be  of  two  principal  kinds,  viz.,  excrementitious  and  digestive. 

As  an  excrementitious  substance,  the  bile  serves  especially 
as  a  medium  for  the  separation  of  excess  of  carbon  and  hydro- 


THE     BILE  —  MECONIUM.  263 

gen  from  the  blood ;  and  its  adaptation  to  this  purpose  is  well 
illustrated  by  the  peculiarities  attending  its  secretion  and  dis- 
posal in  the  foetus.  During  intra-uterine  life,  the  lungs  and 
the  intestinal  canal  are  almost  inactive ;  there  is  no  respiration 
of  open  air  or  digestion  of  food  ;  these  are  unnecessary,  because 
of  the  supply  of  well-elaborated  nutriment  received  by  the 
vessels  of  the  foetus  at  the  placenta.  The  liver,  during  the 
same  time,  is  proportionally  larger  than  it  is  after  birth,  and 
the  secretion  of  bile  is  active,  although  there  is  no  food  in  the 
intestinal  canal  upon  which  it  can  exercise  any  digestive 
property.  At  birth,  the  intestinal  canal  is  full  of  thick  bile, 
mixed  with  intestinal  secretion  ;  for  the  meconium,  or  faeces  of 
the  fcetus,  are  shown  by  the  analyses  of  Simon  and  of  Frerichs 
to  contain  all  the  essential  principles  of  bile. 

Composition  of  Meconium  (Frerichs) : 

Biliary  resin,         .......  15.6 

Common  fat  and  cholesterin,        ....  15.4 

Epithelium,  mucus,  pigment,  and  salts,       .         .  69 

100. 

In  the  foetus,  therefore,  the  main  purpose  of  the  secretion  of 
bile  must  be  the  purification  of  the  blood  by  direct  excretion, 
i.  e.y  by  separation  from  the  blood,  and  ejection  from  the  body 
without  further  change.  Probably  all  the  bile  secreted  in 
foetal  life  is  incorporated  in  the  meconium,  and  with  it  dis- 
charged, and  thus  the  liver  may  be  said  to  discharge  a  function 
in  some  sense  vicarious  of  that  of  the  lungs.  For,  in  the  foetus, 
nearly  all  the  blood  coming  from  the  placenta  passes  through 
the  liver,  previous  to  its  distribution  to  the  several  organs  of 
the  body ;  and  the  abstraction  of  carbon,  hydrogen,  and  other 
elements  of  bile  will  purify  it,  as  in  extra-uterine  life  it  is 
purified  by  the  separation  of  carbonic  acid  and  water  at  the 
lungs. 

The  evident  disposal  of  the  foetal  bile  by  excretion,  makes 
it  highly  probable  that  the  bile  in  extra-uterine  life  is  also,  at 
least  in  part,  destined  to  be  discharged  as  excrementitious. 
But  the  analysis  of  the  faeces  of  both  children  and  adults  shows 
that  (except  when  rapidly  discharged  in  purgation)  they  con- 
tain very  little  of  the  bile  secreted,  probably  not  more  than 
one-sixteenth  part  of  its  weight,  and  that  this  portion  includes 
only  its  coloring,  and  some  of  its  fatty  matters,  but  none  of  its 
essential  principle,  the  bilin.  All  the  bilin  is  again  absorbed 
from  the  intestines  into  the  blood.  But  the  elementary  com- 
position of  bilin  (see  p.  261)  shows  such  a  preponderance  of 
carbon  and  hydrogen,  that  it  cannot  be  appropriated  to  the 
nutrition  of  the  tissues;  therefore,  it  maybe  presumed  that 


264  DIGESTION. 

after  absorption,  the  carbon  and  hydrogen  of  the  bilin  com- 
bining with  oxygen,  are  excreted  as  carbonic  acid  and  water. 
The  destination  of  the  bile  is,  on  this  theory,  essentially  the 
same  in  both  foetal  and  extra-uterine  life;  only,  in  the  former, 
it  is  directly  excreted,  in  the  latter  for  the  most  part  indirectly, 
being,  before  final  ejection,  modified  in  its  absorption  from  the 
intestines,  and  mingled  with  the  blood. 

The  change  from  the  direct  to  the  indirect  mode  of  excre- 
tion of  the  bile  may,  with  much  probability,  be  connected  with 
a  purpose  in  relation  to  the  development  of  heat.  The  tem- 
perature of  the  foetus  is  maintained  by  that  of  the  parent,  and 
needs  no  source  of  heat  within  the  body  of  the  foetus  itself; 
but,  in  extra-uterine  life,  there  is  (as  one  may  say)  a  waste  of 
material  for  heat  when  any  excretion  is  discharged  unoxid- 
ized ;  the  carbon  and  hydrogen  of  the  bilin,  therefore,  instead 
of  being  ejected  in  the  faeces,  are  reabsorbed,  in  order  that 
they  may  be  combined  with  oxygen,  and  that  in  the  combina- 
tion, heat  may  be  generated. 

From  the  peculiar  manner  in  which  the  liver  is  supplied 
with  much  of  the  blood  that  flows  through  it,  it  is  probable, 
as  Dr.  Budd  suggest,  that  this  organ  is  excretory,  not  only 
for  such  hydro-carbonaceous  matters  as  may  need  expulsion 
from  any  portion  of  the  blood,  but  that  it  serves  for  the  direct 
purification  of  the  stream  which,  arriving  by  the  portal  vein, 
has  just  gathered  up  various  substances  in  its  course  through 
the  digestive  organs — substances  which  may  need  to  be  ex- 
pelled, almost  immediately  after  their  absorption.  For  it  is 
easily  conceivable  that  many  things  may  be  taken  up  during 
digestion,  which  not  only  are  unfit  for  purposes  of  nutrition,  but 
which  would  be  positively  injurious  if  allowed  to  mingle  with 
the  general  mass  of  the  blood.  The  liver,  therefore,  may  be 
supposed  placed  in  the  only  road  by  which  such  matters  can 
pass  into  the  general  current,  jealously  to  guard  against  their 
further  progress,  and  turn  them  back  again  into  an  excretory 
channel.  The  frequency  with  which  metallic  poisons  are 
either  excreted  by  the  liver  or  intercepted  and  retained,  often 
for  a  considerable  time,  in  its  own  substance,  may  be  adduced 
as  evidence  for  the  probable  truth  of  this  supposition. 

Though  one  chief  purpose  of  the  secretion  of  bile  may  thus 
appear  to  be  the  purification  of  the  blood  by  ultimate  excre- 
tion, yet  there  are  many  reasons  for  believing  that,  while  it  is 
in  the  intestines,  it  performs  an  important  part  in  the  process 
of  digestion.  In  nearly  all  animals,  for  example,  the  bile  is 
discharged,  not  through  an  excretory  duct  communicating 
with  the  external  surface  or  with  a  simple  reservoir,  as  most 
secretions  are,  but  is  made  to  pass  into  the  intestinal  canal,  so 


FUNCTIONS    OF    THE     LIVER.  265 

as  to  be  mingled  with  the  chyme  directly  after  it  leaves  the 
stomach  ;  an  arrangement,  the  constancy  of  which  clearly  in- 
dicates that  the  bile  has  some  important  relations  to  the  food 
with  which  it  is  thus  mixed.  A  similar  indication  is  furnished 
also  by  the  fact  that  the  secretion  of  bile  is  most  active,  and 
the  quantity  discharged  into  the  intestines  much  greater, 
during  digestion  than  at  any  other  time ;  although,  without 
doubt,  this  activity  of  secretion  during  digestion  may,  how- 
ever, be  in  part  ascribed  to  the  fact  that  a  greater  quantity  of 
blood  is  sent  through  the  portal  vein  to  the  liver  at  this  time, 
and  that  this  blood  contains  some  of  the  materials  of  the  food 
absorbed  from  the  stomach  and  intestines,  which  may  need 
to  be  excreted,  either  temporarily,  to  be  reabsorbed,  or  per- 
manently. 

Respecting  the  functions  discharged  by  the  bile  in  diges- 
tion, there  is  little  doubt  that  it  assists  in  emulsifying  the 
fatty  portions  of  the  food,  and  thus  rendering  them  capable  of 
being  absorbed  by  the  lacteals.  For  it  has  appear  in  some 
experiments  in  which  the  common  bile-duct  was  tied,  that 
although  the  process  of  digestion  in  the  stomach  was  un- 
affected, chyle  was  no  longer  well-formed  ;  the  contents  of  the 
lacteals  consisting  of  clear,  colorless  fluid,  instead  of  being 
opaque  and  white,  as  they  ordinarily  are,  after  feeding.  (2.) 
It  is  probable,  also,  from  the  result  of  some  experiments  by 
Wistinghausen  and  Hoffmann,  that  the  moistening  of  the 
mucous  membrane  of  the  intestines  by  bile  may  facilitate  ab- 
sorption of  fatty  matters  through  it. 

(3.)  The  bile,  like  the  gastric  fluid,  has  a  strongly  antisep- 
tic power,  and  may  serve  to  prevent  the  decomposition  of  food 
during  the  time  of  its  sojourn  in  the  intestines.  The  experi- 
ments of  Tiedemaun  and  Gmelin  show  that  the  contents  of  the 
intestines  are  much  more  fetid  after  the  common  bile-duct  has 
been  tied  than  at  other  times ;  and  the  experiments  of  Bidder 
and  Schmidt  on  animals  with  an  artificial  biliary  fistula,  con- 
firm this  observation ;  moreover,  it  is  found  that  the  mixture 
of  bile  with  a  fermenting  fluid  stops  or  spoils  the  process  of 
fermentation. 

(4.)  The  bile  has  also  been  considered  to  act  as  a  kind  of 
natural  purgative,  by  promoting  an  increased  secretion  of  the 
intestinal  glands,  and  by  stimulating  the  intestines  to  the  pro- 
pulsion of  their  contents.  This  view  receives  support  from 
the  constipation  which  ordinarily  exists  in  jaundice,  from  the 
diarrhrea  which  accompanies  excessive  secretion  of  bile,  and 
from  the  purgative  properties  of  ox-gall. 

Nothing  is  known  with  certainty  respecting  the  changes 
which  the  reabsorbed  portions  of  the  bile  undergo,  either  in 


266  DIGESTION. 

the  intestines  or  in  the  absorbent  vessels.  That  they  are  much 
changed  appears  from  the  impossibility  of  detecting  them  in 
the  blood ;  and  that  part  of  this  change  is  effected  in  the  liver 
is  probable  from  an  experiment  of  Magendie,  who  found  that 
when  he  injected  bile  into  the  portal  vein  a  dog  was  unharmed, 
but  was  killed  when  he  injected  the  bile  into  one  of  the  sys- 
temic vessels. 

The  secretion  of  bile,  as  already  observed,  is  only  one  of  the 
purposes  fulfilled  by  the  liver.  Another  very  important  func- 
tion appears  to  be  that  of  so  acting  upon  certain  constituents 
of  the  blood  passing  through  it,  as  to  render  some  of  them 
capable  of  assimilation  with  blood  generally,  and  to  prepare 
others  for  being  duly  eliminated  in  the  process  of  respiration. 
From  the  labors  of  M.  Bernard,  to  whom  we  owe  most  of  what 
we  know  on  this  subject,  it  appears  that  the  low  form  of  albu- 
minous matter,  or  albuminose,  conveyed  from  the  alimentary 
canal  by  the  blood  of  the  portal  vein,  requires  to  be  submitted 
to  the  influence  of  the  liver  before  it  can  be  assimilated  by  the 
blood  ;  for  if  such  albuminous  matter  is  injected  into  the  jugu- 
lar vein,  it  speedily  appears  in  the  urine ;  but  if  introduced 
into  the  portal  vein,  and  thus  allowed  to  traverse  the  liver,  it 
is  no  longer  ejected  as  a  foreign  substance,  but  is  probably 
incorporated  with  the  albuminous  part  of  the  blood. 

An  important  influence  seems  also  to  be  exerted  by  the  liver 
upon  the  saccharine  matters  derived  from  the  alimentary  canal. 
The  chief  purpose  of  the  saccharine  and  amylaceous  princi- 
ples of  food  is,  probably,  in  relation  to  respiration  and  the 
production  of  animal  heat ;  but  in  order  that  they  may  fulfil 
this,  their  main  office,  it  seems  to  be  essential  that  they  should 
undergo  some  intermediate  change,  which  is  effected  in  the 
liver,  and  which  consists  in  their  conversion  into  a  peculiar 
form  of  saccharine  matter,  very  similar  to  glucose,  or  diabetic 
sugar.  That  such  influence  is  exerted  by .  the  liver  seems 
proved  by  the  fact  that  when  cane  sugar  is  injected  into  the 
jugular  vein  it  is  speedily  thrown  out  of  the  system,  and  ap- 
pears in  the  urine ;  but  when  injected  into  the  portal  vein,  and 
thus  enabled  to  traverse  the  liver,  it  ceases  to  be  excreted  at 
the  kidneys ;  and,  what  is  still  uiore  to  the  point,  a  very  large 
quantity  of  glucose  may  be  injected  into  the  venous  system 
without  any  trace  of  it  appearing  in  the  urine.  So  that  it  may 
be  concluded,  that  the  saccharine  principles  of  the  food  un- 
dergo, in  their  passage  through  the  liver,  some  transformation 
necessary  to  the  subsequent  purpose  they  have  to  fulfil  in  rela- 
tion to  the  respiratory  process,  and  without  which,  such  pur- 
pose probably  could  not  be  properly  accomplished,  and  the 


FORMATION    OF    SUGAR    IN    THE    LIVER.       267 

substances  themselves  would  be  eliminated  as  foreign  matters 
by  the  kidneys. 

Then,  again,  it  was  discovered  by  Bernard,  and  the  dis- 
covery has  been  amply  confirmed,  that  the  liver  possesses  the 
remarkable  property  of  forming  glucose  or  grape-sugar  (C6H13 
O6),  or  a  substance  readily  convertible  into  sugar,  even  out  of 
principles  in  the  blood  which  contain  no  trace  of  saccharine  or 
amylaceous  matter.  In  Herbivora  and  in  animals  living  on 
mixed  diet,  a  large  part  of  the  sugar  is  derived  from  the  sac- 
charine and  amylaceous  principles  introduced  in  their  food. 
But  in  animals  fed  exclusively  on  flesh,  and  deprived  therefore 
of  this  source  of  sugar,  the  liver  furnishes  the  means  whereby 
it  may  be  obtained.  Not  only  in  Carnivora,  however,  but  ap- 
parently in  all  classes  of  animals,  the  liver  is  continually  en- 
gaged, during  health,  in  forming  sugar,  or  a  substance  closely 
allied  to  it,  in  large  amount.  This  substance  may  always  be 
found  in  the  liver,  even  when  absent  from  -all  other  parts  of 
the  body. 

To  demonstrate  the  presence  of  sugar  in  the  liver,  a. portion 
of  this  organ,  after  being  cut  into  small  pieces,  is  bruised  in  a 
mortar  to  a  pulp  with  a  small  quantity  of  water,  and  the  pulp 
is  boiled  with  sulphate  of  soda  in  order  to  precipitate  albu- 
minous and  coloring  matters.  The  decoction  is  then  filtered 
and  may  be  tested  for  glucose.  The  most  usual  test  is  Trom- 
mer's.  To  the  filtered  solution  an  equal  quantity  of  liquor 
potassse  is  added,  with  a  few  drops  of  a  solution  of  sulphate  of 
copper.  The  mixture  is  then  boiled,  when  the  presence  of 
sugar  is  indicated  by  a  reddish-brown  precipitate  of  the  sub- 
oxide  of  copper. 

The  researches  of  Bernard  and  others,  however,  have  shown 
that  the  sugar  is  not  formed  at  once  at  the  liver,  but  that  this 
organ  has  the  power  of  producing  a  peculiar  substance  allied 
to  starch,  which  is  readily  convertible  into  glucose  when  in 
contact  with  any  animal  ferment.  This  substance  has  received 
the  different  names  of  glycogen,  glycogenic  substance,  animal 
starch,  hepatin. 

Glycogen  (C^H^C)^)  is  obtained  by  taking  a  portion  of 
liver  from  a  recently^ killed  animal,  and,  after  cutting  it  into 
small  pieces,  placing  it  for  a  short  time  in  boiling  water.  It 
is  then  bruised  in  a  mortar,  until  it  forms  a  pulpy  mass,  and 
subsequently  boiled  in  distilled  water  for  about  a  quarter  of 
an  hour.  The  glycogen  is  precipitated  from  the  filtered  decoc- 
tion by  the  addition  of  alcohol. 

When  purified,  glycogen  is  a  white,  amorphous,  starch-like 
substance,  odorless  and  tasteless,  soluble  in  water,  but  insoluble 


268  DIGESTION. 

in  alcohol.  It  is  converted  into  glucose  by  boiling  with  dilute 
acids,  or  by  contact  with  any  animal  ferment. 

There  are  two  chief  theories  concerning  the  immediate  desti- 
nation of  glycogen.  (1.)  According  to  Bernard  and  most  other 
physiologists,  its  conversion  into  sugar  takes  place  rapidly 
during  life,  and  the  sugar  is  conveyed  away  by  the  blood  of 
the  hepatic  veins  to  be  consumed  in  respiration  at  the  lungs. 
(2.)  Pavy  and  others  believe  that  the  conversion  into  sugar 
only  occurs  after  death,  and  that  during  life  no  sugar  exists  in 
healthy  livers, — the  amyloid  substance  or  glycogen  being  pre- 
vented by  some  force  from  undergoing  the  transformation. 
The  chief  arguments  advanced  by  Pavy  in  support  of  this  view 
are,  first,  that  scarcely  a  trace  of  sugar  is  found  in  blood  drawn 
during  life  from  the  right  ventricle,  or  in  blood  collected  from 
the  right  side  of  the  heart  immediately  after  an  animal  has 
been  suddenly  deprived  of  life,  while  if  the  examination  be 
delayed  for  a  little  while  after  death,  sugar  in  abundance  may 
be  found  in  such  blood ;  secondly,  that  the  liver,  like  the 
venous,blood  in  the  heart,  is,  at  the  moment  of  death,  almost 
completely  free  from  sugar,  although  afterwards  its  tissue 
speedily  becomes  saccharine,  unless  the  formation  of  sugar  be 
prevented  by  freezing,  boiling,  or  other  means  calculated  to 
interfere  with  the  action  of  a  ferment  on  the  amyloid  substance 
of  the  organ.  Instead  of  adopting  Bernard's  view,  that  nor- 
mally, during  life,  glycogen  passes  as  sugar  into  the  hepatic 
venous  blood,  and  thereby  is  conveyed  to  the  lungs  to  be 
further  disposed  of,  Pavy  inclines  to  believe  that  it  may  repre- 
sent an  intermediate  stage  in  the  formation  of  fat  from  ma- 
terials absorbed  from  the  alimentary  canal. 

For  the  present  we  must  remain  uncertain  as  to  which  of 
these  theories  contains  most  truth  in  it. 

Whatever  be  the  destination  of  this  peculiar  amyloid  sub- 
stance formed  at  the  liver,  most  recent  observers  agree  that  it 
is  formed  at,  and  exists  within,  the  hepatic  cells,  from  which  it 
may  be  extracted  by  the  process  just  described. 

Much  doubt  exists  also  respecting  the  mode  in  which  gly- 
cogen is  formed  in  the  liver,  and  the  materials  which  furnish 
its  source.  Since  its  quantity  is  increased  after  feeding,  espe- 
cially on  substances  containing  much  sugar  or  starch,  it  is 
probable  that  part  of  it  is  derived  from  saccharine  principles 
absorbed  from  the  digestive  canal ;  but  since  its  formation  con- 
tinues even  when  there  is  no  starch  or  sugar  in  the  food,  the 
albuminous  or  fatty  principles  also  have  been  thought  capable 
of  furnishing  part  of  it.  Numerous  experiments,  however, 
having  proved  that  the  liver  continues  to  form  sugar  in  animals 
after  prolonged  starvation,  and  during  hibernation,  and  even 


FORMATION    OF    SUGAR    IN    THE     LIVER.       269 

after  death,  its  production  is  clearly  independent  of  the  ele- 
ments of  food.  One  of  Bernard's  experiments  may  be  quoted 
in  proof  of  this :  Having  fed  a  healthy  dog  for  many  days  ex- 
clusively on  flesh,  he  killed  it,  removed  the  liver  at  once,  and 
before  the  contained  blood  could  have  coagulated,  he  thor- 
oughly washed  out  its  tissue  by  passing  a  stream  of  cold  water 
through  the  portal  vein.  He  continued  the  injection  until  the 
liver  was  completely  exsanguined,  until  the  issuing  water  con- 
tained not  a  trace  of  sugar  or  albumen,  and  until  no  sugar  was 
yielded  by  portions  of  the  organ  cut  into  slices  and  boiled  in 
water.  Having  thus  deprived  the  liver  of  all  saccharine  mat- 
ter, he  left  it  for  twenty-four  hours,  and  on  then  examining  it, 
found  in  its  tissue  a  large  quantity  of  soluble  sugar,  which  must 
clearly  have  been  formed  subsequently  to  the  organ  being 
washed,  and  out  of  some  previously  insoluble  and  non-sac- 
charine substance.  This  and  other  experiments  led  him  and 
others  to  the  conclusion  that  the  formation  of  the  amyloid  sub- 
stance by  the  liver  is  the  result  of  a  kind  of  secretion  or  elabo- 
ration out  of  materials  in  the  solid  tissues  of  the  gland — such 
secretion  being  probably  effected  by  the  hepatic  cells,  in  which, 
indeed,  as  already  observed,  the  substance  has  been  detected. 

According  to  this  view,  then,  the  liver  may  be  regarded  as 
an  organ  engaged  in  forming  two  kinds  of  secretion,  namely, 
bile  and  sugar,  or  rather,  glycogen  readily  convertible  into 
sugar.  The  former,  chiefly  excrementitious,  passes  along  the 
bile-ducts  into  the  intestines,  where  it  may  subserve  some  pur- 
poses in  relation  to  digestion,  and  is  then  for  the  most  part  re- 
absorbed,  and  ultimately  eliminated  during  the  processes  con- 
cerned in  the  production  of  animal  heat.  The  latter,  namely 
sugar,  being  soluble,  is,  unless  Pavy's  view  be  correct,  taken 
up  by  the  blood  in  the  hepatic  vein,  conveyed  through  the 
right  side  of  the  heart  to  the  lungs,  where  it  is  probably  con- 
sumed in  the  respiratory  process,  and  thus  contributes  to  the 
production  of  animal  heat. 

The  formation  of  glycogen  or  of  sugar  is,  like  all  other  pro- 
cesses in  the  living  body,  under  the  control  of  the  nervous  sys- 
tem. Bernard  discovered  that  by  pricking  the  floor  of  the 
fourth  ventricle,  the  quantity  of  sugar  formed  was  so  much  in 
excess  of  the  normal  quantity,  as  to  be  excreted  by  the  kidney, 
and  thus  produce  the  leading  symptom  of  diabetes.  Section  of 
the  inferior  cervical  ganglion  of  the  sympathetic  nerve  also 
produces  diabetes. 

The  channel  by  which  the  influence  of  the  nervous  system, 
is  conducted  in  the  preceding  and  similar  experiments  is  not 
accurately  known  ;  no  theory  having  been  permanently  estab- 
lished, which  explains  all  the  facts  hitherto  observed  in  con- 

23 


270  DIGESTION. 

nection  with  the  influence  of  the  nervous  system  on  the  pro- 
duction of  glucose. 

Summary  of  the  Changes  which  take  place  in  the  Food  during  its 
Passage  through  the  Small  Intestine. 

In  order  to  understand  the  changes  in  the  food  which  occur 
during  its  passage  through  the  small  intestine,  it  will  be  well 
to  refer  briefly  to  the  state  in  which  it  leaves  the  stomach 
through  the  pylorus.  It  has  been  said  before,  that  the  chief 
office  of  the  stomach  is  not  only  to  mix  into  a  uniform  mass 
all  the  varieties  of  food  that  reach  it  through  the  oesophagus, 
but  especially  to  dissolve  the  nitrogenous  portion  by  means  of 
the  gastric  juice.  The  fatty  matters,  during  their  sojourn  in 
the  stomach,  become  more  thoroughly  mingled  with  the  other 
constituents  of  the  food  taken,  but  are  not  yet  in  a  state  fit  for 
absorption.  The  conversion  of  starch  into  sugar,  which  began 
in  the  mouth,  has  been  interfered  with,  although  not  stopped 
altogether.  The  soluble  matters — both  those  which  were  •  so 
from  the  first,  as  sugar  and  saline  matter,  and  those  which 
have  been  made  so  by  the  action  of  the  saliva  and  gastric 
juice — have  begun  to  disappear  by  absorption  into  the  blood- 
vessels, and  the  same  thing  has  befallen  such  fluids  as  may 
have  been  swallowed, — wine,  water,  &c. 

The  thin  pultaceous  chyme,  therefore,  which  during  the 
whole  period  of  gastric  digestion,  is  being  constantly  squeezed 
or  strained  through  the  pyloric  orifice  into  the  duodenum,  con- 
sists of  albuminous  matter,  broken  down,  dissolving  and  half 
dissolved,  fatty  matter,  broken  down,  but  not  dissolved  at  all, 
starch  very  slowly  in  process  of  conversion  into  sugar,  and  as 
it  becomes  sugar,  also  dissolving  in  the  fluids  with  which  it  is 
mixed ;  while  with  these  are  mingled  gastric  fluid,  and  fluid 
that  has  been  swallowed,  together  with  such  portions  of  the 
food  as  are  not  digestible  and  will  be  finally  expelled  as  part 
of  the  fseces. 

On  the  entrance  of  the  chyme  into  the  duodenum,  it  is  sub- 
jected to  the  influence  of  the  fluid  secreted  by  Lieberkiihn's 
and  Brunn's  glands,  before  described,  and  to  that  of  the  bile 
and  pancreatic  juice,  which  are  poured  into  this  part  of  the 
intestine. 

Without  doubt,  that  part  of  digestion  which  it  is  a  chief 
duty  of  the  small  intestine  to  perform,  is  the  alteration  of  the 
fat  in  such  a  manner  as  to  make  it  fit  for  absorption.  And 
there  is  no  doubt  that  this  change  is  chiefly  effected  in  the 
upper  part  of  the  small  intestine.  What  is  the  exact  share  of 
the  process,  however,  allotted  respectively  to  the  bile,  pancreatic 


DIGESTION     IN    SMALL     INTESTINE.  271 

secretion,  and  the  secretion  of  the  intestinal  glands,  is  still  un- 
certain. It  is  most  probable,  however,  that  the  pancreatic 
secretion  and  the  bile  are  the  main  agents  in  emulsifying  the 
fat,  and  that  they  do  this  by  direct  admixture  with  it.  They 
also  promote  its  absorption  by  moistening  the  surface  of  the 
villi  (p.  265). 

During  digestion  in  the  small  intestine,  the  villi  become 
turgid  with  blood,  their  epithelial  cells  become  filled,  by  ab- 
sorption, with  fat-globules,  which,  after  minute  division,  trans- 
ude into  the  granular  basis  of  the  villus,  and  thence  into  the 
lacteal  vessel  in  the  centre,  by  which  they  are  conveyed  along 
the  mesentery  to  the  lymphatic  glands,  and  thence  into  the 
thoracic  duct.  A  part  of  the  fat  is  also  absorbed  by  the  blood- 
vessels of  the  intestine.  The  term  chyle  is  sometimes  applied 
to  the  emulsified  contents  of  the  intestine  after  their  admixture 
with  the  bile  and  pancreatic  juice;  but  more  strictly  to  the 
fluid  contained  in  the  lacteal  vessels  during  digestion,  which 
differs  from  ordinary  lymph  contained  in  the  same  vessels  at 
other  times,  chiefly  in  the  greatly  increased  quantity  of  fat 
particles  which  have  been  absorbed  from  the  small  intestine. 

Although  the  most  evident  function  of  the  small  intestine  is 
the  digestion  of  fat,  it  must  not  be  forgotten  that  a  great  part 
of  the  other  constituents  of  the  food  is  by  no  means  completely 
digested  when  it  leaves  the  stomach.  Indeed,  its  leaving  it 
unabsorbed  would,  alone,  be  proof  of  this  fact. 

The  albuminous  substances  which  have  been  partly  dissolved 
in  the  stomach  continue  to  be  acted  on  by  the  gastric  juice 
which  passes  into  the  duodenum  with  them,  and  the  effect  of 
the  last-named  secretion  is  assisted  or  complemented  by  that 
of  the  pancreas  and  intestinal  glands.  As  the  albuminous 
matters  are  dissolved,  they  are  absorbed  chiefly  by  the  blood- 
vessels, and  only  to  a  small  extent,  probably,  by  the  lacteals. 

The  starchy,  or  amylaceous  portion  of  the  food,  the  conver- 
sion of  which  into  dextrin  and  sugar  was  more  or  less  inter- 
rupted during  its  stay  in  the  stomach,  is  now  acted  on  briskly 
by  the  secretion  of  the  pancreas,  and  of  Brunn's  glands,  and 
perhaps  of  Lieberkuhn's  glands  also,  and  the  sugar  as  it  is 
formed  dissolves  in  the  intestinal  fluids,  and  afterwards,  like 
the  albumen,  is  absorbed  chiefly  by  the  bloodvessels. 

The  liquids,  swallowed  as  such,  which  may  have  escaped 
absorption  in  the  stomach,  are  absorbed  probably  very  soon 
after  their  entrance  into  the  intestine ;  the  fluidity  of  the  con- 
tents of  the  latter  being  preserved  more  by  the  constant  secre- 
tion of  fluid  by  the  intestinal  glands,  pancreas,  and  liver,  than 
by  any  given  portion  of  fluid,  whether  swallowed  or  secreted, 
remaining  long  unabsorbed.  From  this  fact,  therefore,  it  may 


272  DIGESTION. 

be  gathered  that  there  is  a  kind  of  circulation  constantly  pro- 
ceeding from  the  intestines  into  the  blood,  and  from  the  blood 
into  the  intestines  again ;  for,  as  all  the  fluid,  probably  a  very 
large  amount,  secreted  by  the  intestinal  glands,  must  come 
from  the  blood,  the  latter  would  be  too  much  drained,  were  it 
not  that  the  same  fluid  after  secretion  is  again  reabsorbed  into 
the  current  of  blood — going  into  the  blood  charged  with  nutrient 
products  of  digestion,  coming  out  again  by  secretion  through 
the  glands  in  a  comparatively  uncharged  condition. 

It  has  been  said  before  that  the  contents  of  the  stomach  dur- 
ing gastric  digestion  have  a  strongly  acid  reaction.  On  the 
entrance  of  the  chyme  into  the  small  intestine,  this  is  gradu- 
ally neutralized  to  a  greater  or  less  degree  by  admixture  with 
the  bile  and  other  secretions  with  which  it  is  mixed,  and  the 
acid  reaction  becomes  less  and  less  strongly  marked  as  the 
chyme  passes  along  the  canal  towards  the  ileo-csecal  valve. 

Thus,  all  the  materials  of  the  food  are  acted  on  in  the  small 
intestine,  and  a  great  portion  of  the  nutrient  matter  is  absorbed, 
the  fat  chiefly  by  the  lacteals,  the  other  principles,  when  in 
a  state  of  solution,  chiefly  by  the  bloodvessels,  but  neither,  prob- 
ably, exclusively  by  one  set  of  vessels.  At  the  lower  end  of 
the  small  intestine,  the  chyme,  still  thin  and  pultaceous,  is  of 
a  light  yellow  color,  and  has  a  distinctly  fecal  odor.  In  this 
state  it  passes  through  the  ileo-csecal  opening  into  the  large 
intestine. 

Summary  of  the  Process  of  Digestion  in  the  Large  Intestine. 

The  changes  which  take  place  in  the  chyme  after  its  passage 
from  the  small  into  the  large  intestine  are  probably  only  the 
continuation  of  the  same  changes  that  occur  in  the  course  of 
the  food's  passage  through  the  upper  part  of  the  intestinal 
canal.  From  the  absence  of  villi,  however,  we  may  conclude 
that  absorption,  especially  of  fatty  matter,  is  in  great  part  com- 
pleted in  the  small  intestine,  while,  from  the  still  half-liquid, 
pultaceous  consistence  of  the  chyme  when  it  first  enters  the 
caecum,  there  can  be  no  doubt  that  the  absorption  of  liquid  is 
not  by  any  means  concluded.  The  peculiar  odor,  moreover, 
which  is  acquired  after  a  short  time  by  the  contents  of  the 
large  bowel,  would  seem  to  indicate  the  addition  to  them,  in 
this  region,  of  some  special  matter,  probably  excretory.  The 
acid  reaction,  which  had  become  less  and  less  distinct  in  the 
small  bowel,  again  becomes  very  manifest  in  the  caecum — prob- 
ably from  acid  fermentation  processes  in  some  of  the  materials 
of  the  food. 


DIGESTION    IN     LARGE    INTESTINE.  273 

There  seems  no  reason,  however,  to  conclude  that  any  special, 
"  secondary,"  digestive  process  occurs  in  the  caecum  or  in  any 
other  part  of  the  large  intestine.  Probably  any  constituent 
of  the  food  which  has  escaped  digestion  and  absorption  in  the 
small  bowel  may  be  digested  in  the  large  intestine;  and  the 
power  of  this  part  of  the  intestinal  canal  to  digest  fatty,  albu- 
minous, or  other  matters,  may  be  gathered  from  the  good 
effects  of  nutrient  enemata,  so  frequently  given  when  from 
any  cause  there  is  difficulty  in  introducing  food  into  the  stom- 
ach. In  ordinary  healthy  digestion,  however,  the  changes  which 
ensue  in  the  chyme  after  its  passage  into  the  large  intestine, 
are  mainly  the  absorption  of  the  more  liquid  parts,  and  the 
addition  of  the  special  excretory  products  which  give  it  the 
characteristic  odor.  At  the  same  time,  as  before  said,  it  is 
probable  that  a  certain  quantity  of  nutrient  matter  always 
escapes  digestion  in  the  small  intestine,  and  that  this  happens 
more  especially  when  food  has  been  taken  in  excess,  or  when 
it  is  of  such  a  kind  as  to  be  difficult  of  digestion.  Under 
these  circumstances  there  is  no  doubt  that  such  changes  as 
were  proceeding  in  it  at  the  lower  part  of  the  ileum  may 
go  on  unchecked  in  the  large  bowel, — the  process  being  as- 
sisted by  the  secretion  of  the  numerous  tubular  glands  therein 
present. 

By  these  means  the  contents  of  the  large  intestine,  as  they 
proceed  towards  the  rectum,  become  more  and  more  solid,  and 
losing  their  more  liquid  and  nutrient  parts,  gradually  acquire 
the  odor  and  consistence  characteristic  of  faeces.  After  a 
sojourn  of  uncertain  duration  in  the  rectum,  they  are  finally 
expelled  by  the  contraction  of  its  muscular  coat,  aided,  under 
ordinary  circumstances,  by  the  contraction  of  the  abdominal 
muscles. 

For  a  description  of  the  mechanism  by  which  the  act  of 
defecation  is  accomplished,  see  p.  183. 

The  average  quantity  of  solid  fecal  matter  evacuated  by 
the  human  adult  in  twenty-four  hours  is  about  five  ounces ; 
an  uncertain  proportion  of  which  consists  simply  of  the  undi- 
gested or  chemically  modified  residue  of  the  food  and  the  re- 
mainder of  certain  matters  which  are  excreted  in  the  intesti- 
nal canal. 


274  DIGESTION. 


Composition  of  Fences. 

Water, 733  00 

Solids, 267.00 

Special  excrei»entitious  constituents  :  Excretin, 
excretoleic  acid  (Marcet),  and  steroorin 
(Austin  Flint). 

Salts  :     Chiefly  phosphate  of  magnesia  and  phos- 
phate of  lime,  with  small  quantities  of  iron,     | 
soda,  lime,  and  silica. 

Insoluble   residue   of    the   food    (chiefly   starch,     \     267.00 
grains,  woody  tissue,  particles  of  cartilage, 
and  fibrous  tissue,  undigested  muscular  fibres 
or  fat,  and  the  like,  with  insoluble  substances 
accidentally  introduced  with  the  food). 

Mucus,  epithelium,  altered  coloring  matter  of  bile, 
fatty  acids,  &c.  j 

The  time  occupied  by  the  journey  of  a  given  portion  of  food 
from  the  stomach  to  the  anus,  varies  considerably  even  in 
health,  and  on  this  account,  probably,  it  is  that  such  different 
opinions  have  been  expressed  in  regard  to  the  subject.  Dr. 
Brinton  supposes  twelve  hours  to  be  occupied  by  the  journey 
of  an  ordinary  meal  through  the  small  intestine,  and  twenty- 
four  to  thirty-six  hours  by  the  passage  through  the  large 
bowel. 


On  the  Gases  contained  in  the  Stomach  and  Intestines. 

It  need  scarcely  be  remarked  that,  under  ordinary  circum- 
stances, the  alimentary  canal  contains  a  considerable  quantity 
of  gaseous  matter.  Any  one  who  has  had  occasion,  in  a  post- 
mortem examination,  either  to  lay  open  the  intestines,  or  to  let 
out  the  gas  which  they  contain,  must  have  been  struck  by  the 
small  space  afterwards  occupied  by  the  bowels,  and  by  the 
large  degree,  therefore,  in  which  the  gas,  which  naturally  dis- 
tends them,  contributes  to  fill  the  cavity  of  the  abdomen.  In- 
deed, the  presence  of  air  in  the  intestines  is  so  constant,  and, 
within  certain  limits,  the  amount  in  health  so  uniform,  that 
there  can  be  no  doubt  that  its  existence  here  is  not  a  mere  ac- 
cident, but  intended  to  serve  a  definite  and  important  purpose, 
although,  probably,  a  mechanical  one. 

The  sources  of  the  gas  contained  in  the  stomach  and  bowels 
may  be  thus  enumerated : 

1.  Air  introduced   in  the  act  of   swallowing  either  food  or 
saliva. 

2.  Gases   developed   by  the   decomposition   of  alimentary 


MOVEMENTS    OF    THE     INTESTINES. 


275 


matter,  or  of  the  secretions  and  excretions  mingled  with  it  in 
the  stomach  and  intestines. 

3.  It  is  probable  that  a  certain  mutual  interchange  occurs 
between  the  gases  contained  in  the  alimentary  canal,  and  those 
present  in  the  blood  of  the  gastric  and  intestinal  bloodvessels ; 
but  the  conditions  of  the  exchange  are  not  known,  and  it  is 
very  doubtful  whether  anything  like  a  true  and  definite  secre- 
tion of  gas  from  the  blood  into  the  intestines  or  stomach  ever 
takes  place.  There  can  be  no  doubt,  however,  that  the  intes- 
tines may  be  the  proper  excretory  organs  for  many  odorous 
and  other  substances,  either  absorbed  from  the  air  taken  into 
the  lungs  in  inspiration,  or  absorbed  in  the  upper  part  of  the 
alimentary  canal,  again  to  be  excreted  at  a  portion  of  the  same 
tract  lower  down — in  either  case  assuming  rapidly  a  gaseous 
form  after  their  excretion,  and  in  this  way,  perhaps,  obtaining 
a  more  ready  egress  from  the  body. 

It  is  probable  that,  under  ordinary  circumstances,  the  gases 
of  the  stomach  and  intestines  are  derived  chiefly  from  the 
second  of  the  sources  which  have  been  enumerated. 

Tabular  Analysis  of  Gases  contained  in  the  Alimentary  Canal. 


Whence  obtained. 

Composition  by  Volume. 

Oxygen 

Nitrog. 

Carbon. 
Acid. 

Hydrog. 

Carburet. 
Hydrogen. 

Sulphuret. 
Hydrogen. 

Stomach,      .     .     . 
Small  Intestine,    . 
Caecum,  .... 
Colon,     .... 

11 

71 
32 
66 
35 
46 
22 

14 
30 
12 
57 
43 
41 

4 

38 
8 
6 

19 

13 
8 
11 
19 

y  trace. 

J  » 

Rectum,  .... 
Expelled  per  anum 

The  above  tabular  analysis  of  the  gases  contained  in  the 
alimentary  canal  has  been  quoted  from  the  analyses  of  Jurine, 
Magendie,  Marchand,  and  Chevreul,  by  Dr.  Brinton,  from 
whose  work  the  above  enumeration  of  the  sources  of  the  gas 
has  been  also  taken. 


Movements  of  the  Intestines. 

It  remains  only  to  consider  the  manner  in  which  the  food 
and  the  several  secretions  mingled  with  it  are  moved  through 
the  intestinal  canal,  so  as  to  be  slowly  subjected  to  the  in- 
fluence of  fresh  portions  of  intestinal  secretion,  and  as  slowly 


276  DIGESTION. 

exposed  to  the  absorbent  power  of  all  the  villi  and  blood- 
vessels of  the  mucous  membrane.  The  movement  of  the  intes- 
tines is  peristaltic  or  vermicular,  and  is  effected  by  the  alternate 
contractions  and  dilatations  of  successive  portions  of  the  intes- 
tinal coats.  The  contractions,  which  may  commence  at  any 
point  of  the  intestine,  extend  in  a  wave-like  manner  along  the 
tube.  In  any  given  portion,  the  longitudinal  muscular  fibres 
contract  first,  or  more  than  the  circular ;  they  draw  a  portion 
of  the  intestine  upwards,  or,  as  it  were,  backwards,  over  the  sub- 
stance to  be  propelled,  and  then  the  circular  fibres  of  the  same 
portion  contracting  in  succession  from  above  downwards,  or, 
as  it  were,  from  behind  forwards,  press  on  the  substance  into 
the  portion  next  below,  in  which  at  once  the  same  succession 
of  actions  next  ensues.  These  movements  take  place  slowly, 
and,  in  health,  are  commonly  unperceived  by  the  mind ;  but 
they  are  perceptible  when  they  are  accelerated  under  the  in- 
fluence of  any  irritant. 

The  movements  of  the  intestines  are  sometimes  retrograde  ; 
and  there  is  no  hindrance  to  the  backward  movement  of  the 
contents  of  the  small  intestine.  But  almost  complete  security 
is  afforded  against  the  passage  of  the  contents  of  the  large  into 
the  small  intestine  by  the  ileo-csecal  valve.  Besides,  the  orifice 
of  communication  between  the  ileum  and  caecum  (at  the  bor- 
ders of  which  orifice  are  the  folds  of  mucous  membrane  which 
form  the  valve)  is  encircled  with  muscular  fibres,  the  contrac- 
tion of  which  prevents  the  undue  dilatation  of  the  orifice. 

Proceeding  from  above  downwards,  the  muscular  fibres  of 
the  large  intestine  become,  on  the  whole,  stronger  in  direct 
proportion  to  the  greater  strength  required  for  the  onward 
moving  of  the  fseces,  which  are  gradually  becoming  firmer. 
The  greatest  strength  is  in  the  rectum,  at  the  termination  of 
which  the  circular  unstriped  muscular  fibres  form  a  strong 
band  called  the  internal  sphincter,  while  an  external  sphincter 
muscle  with  striped  fibres  is  placed  rather  lower  down,  and 
more  externally,  and  holds  the  orifice  close  by  a  constant 
slight  contraction  under  the  influence  of  the  spinal  cord. 

The  peculiar  condition  of  the  sphincter,  in  relation  to  the 
nervous  system,  will  be  again  referred  to.  The  remaining 
portion  of  the  intestinal  canal  is  under  the  direct  influence  of 
the  sympathetic  or  ganglionic  system,  and,  indirectly,  or  more 
distantly,  is  subject  to  the  influence  of  the  brain  and  spinal 
cord,  which  influence  appears  to  be,  in  some  degree,  transmitted 
through  the  vagus  nerve.  Experimental  irritation  of  the  brain 
or  cord  produces  no  evident  or  constant  effect  on  the  move- 
ments of  the  intestines  during  life ;  yet  in  consequence  of  cer- 
tain conditions  of  the  mind,  the  movements  are  accelerated  or 


LYMPHATIC    VESSELS    AND    GLANDS.        277 

retarded  ;  and  in  paraplegia  the  intestines  appear  after  a  time 
much  weakened  in  their  power,  and  costiveness,  with  a  tym- 
panitic  condition,  ensues.  Immediately  after  death,  irritation 
of  both  the  sympathetic  and  pneumogastric  nerves,  if  not  too 
strong,  induces  genuine  peristaltic  movements  of  the  intestines. 
Violent  irritation  stops  the  movements.  These  stimuli  act,  no 
doubt,  not  directly  on  the  muscular  tissue  of  the  intestine,  but 
on  the  rich  ganglionic  structure  shown  by  Meissner  to  exist  in 
the  submucous  tissue.  This  regulates  and  controls  the  move- 
ments, and  gives  to  them  their  peculiar  slow,  orderly,  rhyth- 
mic, and  peristaltic  character,  both  naturally,  and  when  arti- 
ficiallv  excited. 


CHAPTER  X. 

ABSORPTION. 

THE  process  of  absorption  has,  for  one  of  its  objects,  the  in- 
troduction into  the  blood  of  fresh  materials  from  the  food  and 
air,  and  of  whatever  comes  into  contact  with  the  external  or 
internal  surfaces  of  the  body  ;  and,  for  another,  the  taking 
away  of  parts  of  the  body  itself,  when,  having  fulfilled  their 
office,  or  otherwise  requiring  removal,  they  need  to  be  re- 
newed. In  both  these  offices,  i.  e.,  in  both  absorption  from 
without  and  absorption  from  within,  the  process  manifests  some 
variety,  and  a  very  wide  range  of  action  ;  and  in  both  it  is 
probable  that  two  sets  of  vessels  are,  or  may  be,  concerned, 
namely,  the  bloodvessels,  and  the  lacteals  or  lymphatics,  to 
which  the  term  absorbents  has  been  especially  applied. 

Structure  and  Office  of  the  Lacteal  and  Lymphatic  Vessels  and 

Glands. 

Besides  the  system  of  arteries  and  veins,  with  their  inter- 
mediate vessels,  the  capillaries,  there  is  another  system  of 
canals  in  man  and  other  vertebrata,  called  the  lymphatic  sys- 
tem, which  contains  a  fluid  called  lymph.  Both  these  systems 
of  vessels  are  concerned  in  absorption. 

The  principal  vessels  of  the  lymphatic  system  are,  in  struc- 
ture and  general  appearance,  like  very  small  and  thin-walled 
veins,  and  like  them  are  provided  with  valves.  By  one  ex- 
tremity they  commence  by  fine  microscopic  branches,  the  lym- 
phatic capillaries  or  lymph-capillaries,  in  the  organs  and  tissues 

24 


278 


ABSORPTION. 


of  nearly  every  part  of  the  body,  and  by  their  other  extremi- 
ties they  end  directly  or  indirectly  in  two  trunks  which  open 
into  the  large  veins  near  the  heart  (Fig.  92).  Their  contents, 
the  lymph  and  chyle,  unlike  the  blood,  pass  only  in  one  direc- 


FIG.  92. 


Lymphatics  of  head 
and  neck,  right. 

Right  internal  jug- 
ular vein. 

Right  subclavian 
vein. 

Lymphatics  of  right 
arm. 


Receptaculum 
chyli. 


Lymphatics  of  Icn 
er  extremities 


Lymphatics  of  head 
and  neck,  left. 

Thoracic  duct. 

Left  subclavian 
vein. 


Thoracic  duct. 


Lacteals. 


Lymphatics  of  low- 
er extremities. 


Diagram  of  the  principal  groups  of  lymphatic  vessels  (from  Quain). 

tion,  namely,  from  the  fine  branches  to  the  trunk  and  so  to 
the  large  veins,  on  entering  which  they  are  mingled  with  the 
stream  of  blood,  and  form  part  of  its  constituents.  Remem- 
bering the  course  of  the  fluid  in  the  lymphatic  vessels,  viz.,  its 
passage  in  the  direction  only  towards  the  large  veins  in  the 
neighborhood  of  the  heart,  it  will  be  readily  seen  from  Fig.  92 
that  the  greater  part  of  the  contents  of  the  lymphatic  system 
of  vessels  passes  through  a  comparatively  large  trunk  called 


COURSE    OF    THE    LYMPHATICS. 


279 


the  thoracic  duct,  which  finally  empties  its  contents  into  the 
blood-stream  at  the  junction  of  the  internal  jugular  and  sub- 
clavian  veins  of  the  left  side.  There  is  a  smaller  duct  on  the 
right  side.  The  lymphatic  vessels  of  the  intestinal  canal  are 
called  lacteals,  because,  during  digestion,  the  fluid  contained 
in  them  resembles  milk  in  appearance ;  and  the  lymph  in  the 
lacteals  during  the  period  of  digestion  is  called  chyle.  There 


FIG.  93. 


Lymphatic  vessels  of  the  head  and  neck  of  the  upper  part  of  the  trunk  (from  Mas- 
oagni)  lr  — Tne  chest  and  pericardium  have  been  opened  on  the  left  side,  and  the 
left  mamma  detached  and  thrown  outwards  over  the  left  arm,  so  as  to  expose  a  great 
part  of  its  deep  surface.  The  principal  lymphatic  vessels  and  glands  are  shown  on 
the  side  of  the  head  and  face,  and  in  the  neck,  axiila,  and  mediastinum.  Between 
the  left  internal  jugular  vein  and  the  common  carotid  artery,  the  upper  ascending 
part  of  the  thoracic  duct  marked  1,  and  above  this,  and  descending  to  2,  the  arch 
and  last  part  of  tin-  duct.  The  termination  of  the  upper  lymphatics  of  the  diaphragm 
in  the  mediastinal  glands  as  well  as  the  cardiac  and  the  deep  mammary  lymphatics, 
are  also  shown. 


280  ABSORPTION. 

is  no  essential  distinction,  however,  between  lacteals  and  lym- 
phatics. 

In  some  part  of  their  course  all  lymphatic  vessels  pass  through 
certain  bodies  called  lymphatic  glands. 

Lymphatic  vessels  are  distributed  in  nearly  all  parts  of  the 
body.  Their  existence,  however,  has  not  yet  been  determined 
in  the  placenta,  the  umbilical  cord,  the  membranes  of  the  ovum, 
or  in  any  of  the  non-vascular  parts,  as  the  nails,  cuticle,  hair, 
and  the  like. 

The  lymphatic  capillaries  commence  most  commonly  either 
in  closely-meshed  networks,  or  in  irregular  lacunar  spaces 
between  the  various  structures  of  which  the  different  organs 
are  composed.  The  former  is  the  rule  of  origin  with  those 
lymphatics  which  are  placed  most  superficially,  as,  for  instance, 
immediately  beneath  the  skin,  or  under  the  mucous  and  serous 
membranes ;  while  the  latter  is  most  common  with  those  which 
arise  in  the  substance  of  organs.  In  the  former  instance,  their 
walls  are  composed  of  but  little  more  than  homogeneous  mem- 
brane, lined  by  a  single  layer  of  epithelial  cells,  very  similar 
to  those  which  line  the  blood-capillaries  (Fig.  49).  In  the 
latter  instance  the  small  irregular  channels  and  spaces  from 
which  the  lymphatics  take  their  origin,  although  they  are 
formed  mostly  by  the  chinks  and  crannies  between  the  blood- 
vessels, secreting  ducts,  and  other  parts  which  may  happen  to 
form  the  framework  of  the  organ  in  which  they  exist,  yet  have 
also  a  layer  of  epithelial  cells  to  define  and  bound  them. 

The  lacteals  apear  to  offer  an  illustration  of  another  mode 
of  origin,  namely,  in  blind  dilated  extremities  (Figs.  81,  82) ; 
but  there  is  no  essential  difference  in  structure  between  these 
and  the  lymphatic  capillaries  of  other  parts. 

Recent  discoveries  seem  likely  to  put  an  end  soon  to  the 
long-standing  discussion  whether  any  direct  communications 
exist  between  the  lymph-capillaries  and  blood-capillaries ;  the 
need  for  any  special  intercommunicating  channels  seeming  to 
disappear  in  the  light  of  more  accurate  knowledge  of  the  struc- 
ture and  endowments  of  the  parts  concerned.  For  while,  on 
the  one  hand,  the  fluid  part  of  the  blood  constantly  exudes  or 
is  strained  through  the  walls  of  the  blood-capillaries,  so  as  to 
moisten  all  the  surround  ing  tissues,  and  occupy  the  interspaces 
which  exist  among  their  different  elements,  these  same  inter- 
spaces have  been  shown,  as  just  stated,  to  form  the  beginnings 
of  the  lymph-capillaries.  And  while,  for  many  years,  the  no- 
tion of  the  existence  of  any  such  channels  between  the  blood- 
vessels and  lymphvessels,  as  would  admit  blood-corpuscles,  has 
been  given  up,  recent  observations  have  proved  that,  for  the 
passage  of  such  corpuscles,  it  is  not  necessary  to  assume  the 


ORIGIN    OF    LYMPHATICS. 


281 


presence  of  any  special  channels  at  all,  inasmuch    as  blood- 
corpuscles  can  pass  bodily,  without  much  difficulty,  through 


FIG.  94. 


FIG.  95. 


FIG.  94.— Superficial  lymphatics  of  the  forearm  and  palm  of  the  hand,  £  (after 
Mascagni).  5.  Two  small  glands  at  the  bend  of  the  arm.  6.  Radial  lymphatic  ves- 
sels. 7.  Dinar  lymphatic  vessels.  8,  8.  Palmar  arch  of  lymphatics.  9,  9'.  Outer 
and  inner  sets  of  vessels,  b.  Cephalic  vein.  d.  Radial  vein.  e.  Median  vein.  /. 
Dinar  vein.  The  lymphatics  are  represented  as  lying  on  the  deep  fascia. 

FIG.  95. — Superficial  lymphatics  of  right  groin  and  upper  part  of  thigh,  1  (after 
Mascagni).  1.  Dpper  inguinal  glands.  2'.  Lower  inguinal  or  femoral  glands.  3,  3. 
Plexus  of  lymphatics  in  the  course  of  the  long  saphenous  vein. 


282  ABSORPTION. 

the  walls  of  the  blood-capillaries  and  small  veins  (p.  138),  and 
could  pass  with  still  less  trouble,  probably,  through  the  com- 
paratively ill-defined  wralls  of  the  capillaries  which  contain 
lymph. 

Observations  of  Recklinghausen  have  led  to  the  discovery 
that  in  certain  parts  of  the  body  openings  exist  by  which  lym- 
phatic capillaries  directly  communicate  with  parts  hitherto 
supposed  to  be  closed  cavities.  If  the  peritoneal  cavity  be  in- 
jected with  milk,  an  injection  is  obtained  of  the  plexus  of  lym- 
phatic vessels  of  the  central  tendon  of  the  diaphragm ;  and  on 
removing  a  small  portion  of  the  central  tendon,  with  its  peri- 
toneal surface  uninjured,  and  examining  the  process  of  absorp- 
tion under  the  microscope,  Recklinghausen  noticed  that  the 
milk-globules  ran  towards  small  natural  openings  or  stomata 
between  the  epithelial  cells,  and  disappeared  by  passing  vortex- 
like  through  them.  The  stomata,  which  had  a  roundish  out- 
line, were  only  wide  enough  to  admit  two  or  three  milk-glob- 
ules abreast,  and  never  exceeded  the  size  of  an  epithelial  cell. 
Openings  of  a  similar  kind  have  been  found  by  Dybskowsky 
in  the  pleura ;  and  as  they  may  be  presumed  to  exist  in  other 
serous  membranes,  it  would  seem  as  if  the  serous  cavities, 
hitherto  supposed  closed,  form  but  a  large  widening  out,  so  to 
speak,  of  the  lymph-capillary  system  with  which  they  directly 
communicate. 

In  structure,  the  medium-sized  and  larger  lymphatic  vessels 
are  very  like  veins ;  having,  according  to  Kolliker,  an  exter- 
nal coat  of  fibro-cellular  tissue,  with  elastic  filaments ;  within 
this,  a  thin  layer  of  fibro-cellular  tissue,  with  organic  muscu- 
lar fibres,  which  have,  principally,  a  circular  direction,  and  are 
much  more  abundant  in  the  small  than  in  the  larger  vessels  ; 
and  again,  within  this,  an  inner  elastic  layer  of  longitudinal 
fibres,  and  a  lining  of  epithelium,  and  numerous  valves.  The 
valves,  constructed  like  those  of  veins,  and  with  the  free  edges 
turned  towards  the  heart,  are  usually  arranged  in  pairs,  and, 
in  the  small  vessels,  are  so  closely  placed,  that  when  the  vessels 
are  full,  the  valves  constricting  them  where  their  edges  are 
attached,  give  them  a  peculiar  braided  or  knotted  appearance 
(Fig.  99). 

With  the  help  of  the  valvular  mechanism,  all  occasional 
pressure  on  the  exterior  of  the  lymphatic  and  lacteal  vessels 
propels  the  lymph  towards  the  heart:  thus  muscular  and 
other  external  pressure  accelerates  the  flow  of  the  lymph  as 
it  does  that  of  the  blood  in  the  veins  (see  p.  143).  The 
actions  of  the  muscular  fibres  of  the  small  intestine,  and 
probably  the  layer  of  organic  muscle  present  in  each  intesti- 
nal villus  (p.  246),  seem  to  assist  in  propelling  the  chyle :  for, 


LYMPHATIC    GLANDS.  283 

in  the  small  intestine  of  a  mouse,  Poiseuille  saw  the  chyle 
moving  with  intermittent  propulsions  that  appeared  to  corre- 
spond with  the  peristaltic  movements  of  the  intestine.  But  for 
the  general  propulsion  of  the  lymph  and  chyle,  it  is  probable 
that,  together  with  the  vis  a  tergo  resulting  from  absorption 
(as  in  the  ascent  of  sap  in  a  tree),  and  from  external  pressure, 
some  of  the  force  may  be  derived  from  the  contractility  of  the 
vessel's  own  walls.  Kolliker,  after  watching  the  lymphatics 
in  the  transparent  tail  of  the  tadpole,  states  that  no  distinct 
movements  of  their  walls  can  ever  be  seen,  but  as  they  are 
emptied  after  death  they  gradually  contract,  and  then,  after 
some  time,  again  dilate  to  their  former  size,  exactly  as  the 
small  arteries  do  under  the  like  circumstances.  Thus,  also, 
the  larger  vessels  in  the  human  subject  commonly  empty 
themselves  after  death  ;  so  that,  although  absorption  is  proba- 
bly usually  going  on  just  before  the  time  of  death,  it  is  not 
common  to  see  the  lymphatic  or  lacteal  vessels  full.  Their 
power  of  contraction  under  the  influence  of  stimuli  has  been 
demonstrated  by  Kolliker,  who  applied  the  wire  of  an  electro- 
magnetic apparatus  to  some  well-filled  lymphatics  on  the 
skin  of  a  boy's  foot,  just  after  the  removal  of  his  leg  by  am- 
putation, and  noticed  that  the  calibre  of  the  vessels  diminished 
at  least  one  half.  It  is  most  probable  that  this  contraction 
of  the  vessels  occurs  during  life,  and  that  it  consists,  not  in 
peristaltic  or  undulatory  movements,  but  in  a  uniform  con- 
traction of  the  successive  portions  of  the  vessels,  by  which 
pressure  is  steadily  exercised  upon  their  contents,  and  which 
alternates  with  their  relaxation. 

Lymphatic  Glands. 

Almost  all  lymphatic  and  lacteal  vessels  in  some  part  of 
their  course  pass  through  one  or  more  small  bodies  called  lym- 
phatic glands  (Fig.  99). 

A  lymphatic  gland  is  covered  externally  by  a  capsule  of 
connective  tissue,  which  invests  and  supports  the  glandular 
structure  within  ;  while  prolonged  from  its  inner  surface  are 
processes  QYtrabeculw  which,  entering  the  gland  from  all  sides, 
and  freely  communicating,  form  a  fibrous  scaffolding  or  strorna 
in  all  parts  of  the  interior.  Thus  are  formed  in  the  outer  or 
cortical  part  of  the  glands  (Fig.  96),  in  the  intervals  of  the 
trabeculse,  certain  intercommunicating  spaces  termed  alveoli; 
while  a  finer  meshwork  is  formed  in  the  more  central  or 
medullary  part.  In  the  alveoli  and  the  trabecular  meshwork 
the  proper  gland-substance  is  contained ;  in  the  form  of  nod- 


284 


ABSORPTION. 


ules  in  the  cortical  alveoli,  and  of  rounded  cords  in  the 
medullary  part  (Fig.  97).  The  gland-substance  of  one  part 
is  continuous  directly  or  indirectly  with  that  of  all  others. 


FIG.  96. 


Section  of  a  mesenteric  gland  from  the  ox,  slightly  magnified,  a,  hilus ;  b  (in  the 
central  part  of  the  figure),  medullary  substance  ;  c,  cortical  substance  with  indis- 
tinct alveoli ;  d,  capsule  (after  Kolliker). 

The  essential  structure  of  lymphatic  gland-substance  resem- 
bles that  which  was  described  as  existing,  in  a  simple  form,  in 
the  interior  of  the  solitary  and  agminated  intestinal  follicles 


FIG.  97. 


Section  of  medullary  substance  of  an  inguinal  gland  of  an  ox  (magnified  90 
diameters),  a,  a,  glandular  substance  or  pulp  forming  rounded  cords  joining  in  a 
continuous  net  (dark  in  the  figure) ;  c,  c,  trabeculse ;  the  space,  b,  b,  between  these 
and  the  glandular  substance  is  the  lymph-sinus,  washed  clear  of  corpuscles  and 
traversed  by  filaments  of  retiform  connective  tissue  (after  Kolliker). 


LYMPHATIC    GLANDS. 


285 


(p.  242).  Pervading  all  parts  of  it,  and  occupying  the  alveoli 
and  trabecular  spaces  before  referred  to,  is  a  network  of  the 
variety  of  connective  tissue  termed  retiform  tissue  (Fig.  98), 
the  interspaces  of  which  are  occupied  by  lymph-corpuscles. 
The  corpuscles  are  arranged  in  such  a  way,  that  while  in  the 
centre  of  the  alveoli  and  of  each  mesh  they  are  so  crowded 
together  as  to  be,  with  the  retiform  tissue  pervading  them,  a 
consistent  gland-pulp,  continuous  in  the  form  of  the  nodules 
and  cords,  before  referred  to,  throughout  the  whole  gland,  they 
are  in  comparatively  small  numbers  in  the  outer  part  of  the 
alveoli  and  meshes,  and  leave  this  portion,  as  it  were,  open. 


FIG. 


A  small  portion  of  medullary  substance  from  a  mesenteric  gland  of  the  ox  (mag- 
nified 300  diameters),  d,  d,  trabeculse  ;  a,  part  of  a  cord  of  glandular  substances  from 
which  all  but  a  few  of  the  lymph-corpuscles  have  been  washed  out  to  show  its  sup- 
porting meshwork  of  retiform  tissue  and  its  capillary  bloodvessels  (which  have  been 
injected,  and  are  dark  in  the  figure) ;  b,  b,  lymph-sinus,  of  which  the  retiform  tissue 
is  represented  only  at  c,  c  (after  Kolliker). 

(See  Figs.  97,  98.)  This  free  space  between  the  gland-pulp 
and  the  trabecular  stroma,  occupied  only  by  retiform  tissue,  is 
called  the  lymph-channel  or  lymph-path,  because  it  is  traversed 


286  ABSORPTION. 

by  the  lymph,  which  is  continually  brought  to  the  gland  and 
conveyed  away  from  it  by  lymphatic  vessels ;  those  which 
bring  it  being  termed  afferent  vessels,  and  those  which  take  it 
away  efferent  vessels.  The  former  enter  the  cortical  part  of 
the  gland  and  open  into  its  alveoli,  at  the  same  time  that  they 
lay  aside  all  their  coats  except  the  epithelial  lining,  which 
may  be  said  to  continue  to  line  the  lymph-path  into  which  the 
contents  of  the  afferent  vessels  now  pass.  The  efferent  vessels 
begin  in  the  medullary  part  of  the  gland,  and  are  continuous 
with  the  lymph-path  here  as  the  afferent  vessels  were  with  the 
cortical  portion  ;  the  epithelium  of  one  is  continuous  with  that 
of  the  other. 

Bloodvessels  are  freely  distributed  to  the  trabecular  tissue 
and  to  the  gland-pulp  (Fig.  98). 

Properties  of  Lymph  and  Chyle. 

The  fluid,  or  lymph,  contained  in  the  lymphatic  vessels  is, 
under  ordinary  circumstances,  clear,  transparent,  and  color- 
less, or  of  a  pale  yellow  tint.  It  is  devoid  of  smell,  is  slightly 
alkaline,  and  has  a  saline  taste.  As  seen  with  the  micro- 
scope in  the  small  transparent  vessels  of  the  tail  of  the  tad- 
pole, the  lymph  usually  contains  no  corpuscles  or  particles  of 
any  kind ;  and  it  is  probably  only  in  the  larger  trunks  in 
which,  by  a  process  similar  to  that  to  be  described  in  the 
chyle,  the  lymph  is  more  elaborated,  that  any  corpuscles  are 
formed.  These  corpuscles  are  similar  to  those  in  the  chyle, 
but  less  numerous.  The  fluid  in  which  the  corpuscles  float 
is  commonly  and  in  health  albuminous,  and  contains  no  fatty 
particles  or  molecular  base ;  but  it  is  liable  to  variations  ac- 
cording to  the  general  state  of  the  blood,  and  that  of  the  organ 
from  which  the  lymph  is  derived.  As  it  advances  towards  the 
thoracic  duct,  and  passes  through  the  lymphatic  glands,  it  be- 
comes, like  chyle,  spontaneously  coagulable  from  the  formation 
of  fibrin,  and  the  number  of  corpuscles  is  much  increased. 

The  fluid  contained  in  the  lacteals,  or  lymphatic  vessels  of 
the  intestine,  is  clear  and  transparent  during  fasting,  and 
differs  in  no  respect  from  ordinary  lymph ;  but  during  diges- 
tion, it  becomes  milky,  and  is  termed  chyle. 

Chyle  is  an  opaque,  whitish  fluid,  resembling  milk  in  ap- 
pearance, and  having  a  neutral  or  slightly  alkaline  reaction. 
Its  whiteness  and  opacity  are  due  to  the  presence  of  innumer- 
able particles  of  oily  or  fatty  matter,  of  exceedingly  minute 
though  nearly  uniform  size,  measuring  on  the  average  about 
•£00077  of  an  inch  (Gulliver).  These  constitute  what  Mr.  Gul- 


CHYLE. 


287 


liver  appropriately  terms  the  molecular  base  of  chyle.  Their 
number,  and  consequently  the  opac- 
ity of  the  chyle,  are  dependent  upon 
the  quantity  of  fatty  matter  con- 
tained in  the  food.  Hence,  as  a 
rule,  the  chyle  is  whitish  and  most 
turbid  in  carnivorous  animals ;  less 
so  in  Herbivora ;  while  in  birds  it  is 
usually  transparent.  The  fatty  na- 
ture of  the  molecules  is  made  mani- 
fest by  their  solubility  in  ether,  and, 
when  the  ether  evaporates,  by  their 
being  deposited  in  various-sized  drops 
of  oil.1  Yet,  since  they  do  not  run 
together  and  form  a  larger  drop,  as 
particles  of  oil  would,  it  appears  very 
probable  that  each  molecule  consists 
of  oil  coated  over  with  albumen,  in 
the  manner  in  which,  as  Ascherson 
observed,  oil  always  becomes  covered 
when  set  free  in  minute  drops  in  an 
albuminous  solution.  And  this  view 
is  supported  by  the  fact,  that  when 
water  or  dilute  acetic  acid  is  added 
to  chyle,  many  of  the  molecules  are 
lost  sight  of,  and  oil-drops  appear  in  Phatic  sland-  3<  with  its  com- 
their  place,  as  if  the  investments  of  ponent  cellsfilled  with  mercury 

r  ,         ,        111  j-        i       j      and  having  three  sets  of  afferent 

the    molecules  had    been  dissolved,  vessels  ^  ^  ^  leading  into  it 

and    their  oily  Contents    had    run  to-  and  one  set  of  efferent  vessels,  2, 

gether.  passing  out  from  it.    The  arrows 

Except  these  molecules,  the  chyle  indicate  the  course  of  the  lymph 

taken  from  the  villi  Or  from  lacteals  in  these  vessels.    The  varicose  or 

near  them  contains  no  other  solid  or  ££SS7^T? 

Organized  bodies.  1  lie  fluid  in  Which  phatic  vessel  somewhat  enlarged, 
the  molecules  float  is  albuminOUS,  and  cut  through,  to  show  the 
and  does  not  Spontaneously  COagU-  Httle  double  valves  in  its  interior. 
,  ,  .•  i  i  11  v  IT.  jj-  c,  lymph-corpuscles,  one  granu- 

late,  though  coagulable  by  the  addi-  ^  J  three  fcreated  wlth  dilute 
tion  of  ether.  But  as  the  chyle  passes  acetic  acid,  showing  the  envelope 

On  towards  the  thoracic  duct,  and  and  the  pale  nucleus ;  also  some 
especially  while  it  traverses  One  Or  finer  granules  and  oil-particles 

more  of  the  mesenteric  glands  (pro-  free-   Magnified  400  diameters. 

pelled   by  forces  which  have   been 

described  with  the  structure  of  the  vessels),  it  is  elaborated. 


(Mascagni),  a,  plan   of  a  lyi 


1  Some  of  the  molecules  may  remain  undissolved  by  the  ether;  but 
this  appears  to  bo  due  to  their  being  defended  from  the  action  of  the 
ether  by  bein^  entangled  within  the  albumen  which  it  coagulates. 


288  ABSORPTION. 

The  quantity  of  molecules  and  oily  particles  gradually  di- 
minishes; cells,  to  which  the  name  of  chyle-corpuscles  is  given, 
are  developed  in  it;  and  by  the  formation  of  fibrin,  it  acquires 
the  property  of  coagulating  spontaneously.  The  higher  in  the 
thoracic  duct  the  chyle  advances,  the  more  is  it,  in  all  these 
respects,  developed ;  the  greater  is  the  number  of  chyle-cor- 
puscles, and  the  large?  and  firmer  is  the  clot  which  forms  in  it 
when  withdrawn  and  left  at  rest.  Such  a  clot  is  like  one  of 
blood,  without  the  red  corpuscles,  having  the  chyle-corpuscles 
entangled  in  it,  and  the  fatty  matter  forming  a  white  creamy 
film  on  the  surface  of  the  serum.  But  the  clot  of  chyle  is  softer 
and  moister  than  that  of  blood.  Like  blood,  also,  the  chyle 
often  remains  for  a  long  time  in  its  vessels  without  coagu- 
lating, but  coagulates  rapidly  on  being  removed  from  them 
(Bouissou).  The  existence  of  fibrin,  or  of  the  materials  which 
by  their  union  form  it  (p.  62  et  seq.\  is,  therefore,  certain ;  its 
increase  appears  to  be  commensurate  with  that  of  the  corpus- 
cles ;  and,  like  them,  it  is  not  absorbed  as  such  from  the  chyme 
(for  no  fibrin  exists  in  the  chyle  in  the  villi),  but  is  gradually 
elaborated  out  of  the  albumen  which  chyle  in  its  earliest  con- 
dition contains. 

The  structure  of  the  chyle-corpuscles  was  described  when 
speaking  of  the  white  corpuscles  of  the  blood,  with  which  they 
are  identical. 

From  what  has  been  said,  is  will  appear  that  perfect  chyle 
and  lymph  are,  in  essential  characters,  nearly  similar,  and 
scarcely  differ,  except  in  the  preponderance  of  fatty  matter  in 
the  chyle.  The  comparative  analysis  of  the  two  fluids  obtained 
from  the  lacteals  and  the  lymphatics  of  a  donkey  is  thus  given 
by  Dr.  Owen  Rees : 

Chyle.  Lymph. 

Water,         .         .  .  90.237  96.536 


Albumen,    . 

Fibrin. 

Animal  extractive, 

Fatty  matter, 

Salts,    . 


3.516  1.200 

0.370  0.120 

1.565  1.559 

3  601  a  trace. 

0.711  0.585 

100000  100.000 


The  analyses  of  Nasse  afford  an  estimate  of  the  relative  com- 
positions of  the  lymph,  chyle,  and  blood  of  the  horse.1 

1  The  analysis  of  the  blood  differs  rathtr  widely  from  that  given  at 
psige  72 ;  but  if  it  be  erroneous,  it  is  probable  that  corresponding  errors 
exist  in  the  analysis  of  the  lymph  and  chyle;  and  that  therefore  the 
tables  in  the  text  may  represent  accurately  enough  the  relation  in. 
which  the  three  fluids  stand  to  each  other. 


COMPOSITION    OF     LYMPH    AND    CHYLE.       289 

Lymph.  Chyle.  Blood. 

Water, 950.  935.  810. 

Corpuscles, ...  4.  92.8 

Albumen,    .  39  11  31.  80 

Fibrin,         .  0.75  2.8 

Extractive  matter,  4.88  6.25  5.2 

Fatty  matter,  0.09  15.  1.55 

Alkaline  salts,  5.61  7.  6.7. 

Phosphateof  lime  and  magnesia,  oxide  )    A  01  i  n  nr 

of  iron,  &c.,  j 

1000.   1000.   1000. 

The  contents  of  the  thoracic  duct,  including  both  the  lymph 
and  chyle  mixed,  in  an  executed  criminal,  were  examined  by 
Dr.  Rees,  who  found  them  to  consist  of — 


Water, 

Albumen  and  fibrin. 
Extractive  matter,  . 
Fatty  " 

Saline  " 


90.48 
7.08 
0.108 
0.92 
0.44 


From  all  these  analyses  of  lymph  and  chyle,  it  appears  that 
they  contain  essentially  the  same  organic  constituents  that  are 
found  in  the  blood,  viz.,  albumen,  fibrin,  and  fatty  matter,  the 
same  saline  substances,  and  iron.  Their  composition  differs 
from  that  of  the  blood  in  degree  rather  than  in  kind ;  they 
contain  a  less  proportion  of  all  the  substances  dissolved  in  the 
water  (see  Nasse's  analyses,  just  quoted),  and  much  less  fibrin. 
The  fibrin1  of  lymph,  besides  being  less  in  quantity,  appears  to 
be  in  a  less  elaborated  state  than  that  of  the  blood,  coagulating 
less  rapidly  and  less  firmly.  According  to  Virchow,  it  never 
coagulates,  under  ordinary  circumstances,  within  the  lymphatic 
vessels,  either  during  life  or  after  death.  These  differences 
gradually  diminish,  while  the  lymph  and  chyle,  passing  to- 
wards and  through  the  thoracic  duct,  gradually  approach  the 
place  at  which  they  are  to  be  mingled  with  the  blood.  For,  in 
the  thoracic  duct,  besides  the  higher  and  more  abundant  de- 
velopment of  the  fibrin,  the  lymph  and  chyle-corpuscles  are 
found  more  advanced  towards  their  development  into  red 
blood-corpuscles;  sometimes  even  that  development  is  com- 
pleted, and  the  lymph  has  a  pinkish  tinge  from  the  number  of 
red  blood-corpuscles  that  it  contains. 

The  general  result,  therefore,  of  both  the  microscopic  and 
the  chemical  examinations  of  the  lymph  and  chyle,  demon~ 
strate  that  they  are  rudimental  blood ;  their  fluid  part  being, 


1  For  observations  on  the  nature  of  fibrin,  see  p.  62. 


290  ABSORPTION. 

like  the  liquor  sanguinis,  diluted,  but  gradually  becoming 
more  concentrated ;  and  their  corpuscles  being  in  process  of 
development  into  red  blood-corpuscles.  Thus,  in  quality,  the 
lymph  and  chyle  are  adapted  to  replenish  the  blood  ;  and  their 
quantity,  so  far  as  it  can  be  estimated,  appears  ample  for  this 
purpose.  In  one  of  Mageudie's  experiments,  half  an  ounce  of 
chyle  was  collected  in  five  minutes  from  the  thoracic  duct  of  a 
middle-sized  dog  ;  Collard  de  Martigny  obtained  nine  grains  of 
lymph,  in  ten  minutes,  from  the  thoracic  duct  of  a  rabbit  which 
had  taken  no  food  for  twenty-four  hours ;  and  Gieger,  from 
three  to  five  pounds  of  lymph  daily  from  the  foot  of  a  horse, 
from  whom  the  same  quantity  had  been  flowing  several  years 
without  injury  to  health.  Bidder  found,  on  opening  the  tho- 
racic duct  in  cats,  immediately  after  death,  that  the  mingled 
lymph  and  chyle  continued  to  flow  from  one  to  six  minutes ; 
and,  from  the  quantity  thus  obtained,  he  estimated  that  if  the 
contents  of  the  thoracic  duct  continued  to  move  at  the  same 
rate,  the  quantity  which  would  pass  into  a  cat's  blood  in  twenty- 
four  hours  would  be  equal  to  about  one-sixth  of  the  weight  of 
the  whole  body.  And,  since  the  estimated  weight  of  the  blood 
in  cats  is  to  the  weight  of  their  bodies  as  1.7,  the  quantity  of 
lymph  daily  traversing  the  thoracic  duct  would  appear  to  be 
about  equal  to  the  quantity  of  blood  at  any  time  contained  in 
the  animals.  Schmidt's  observations  on  foals  have  yielded 
very  similar  results.  By  another  series  of  experiments,  Bidder 
estimated  that  the  quantity  of  lymph  traversing  the  thoracic 
duct  of  a  dog  in  twenty-four  hours  is  about  equal  to  two-thirds 
of  the  blood  in  the  body.  If  we  take  these  estimates,  it  will 
not  follow  from  them  that  the  whole  of  an  animal's  blood  is 
daily  replaced  by  the  development  of  lymph  and  chyle;  for 
even  if  the  quantity  of  lymph  and  chyle  daily  formed  be  equal 
to  that  of  the  blood,  the  solid  contents  of  the  blood  will  be 
much  too  great  to  be  replaced  by  those  of  the  lymph  and  chyle. 
According  to  Nasse's  analyses,  the  solid  matter  of  a  given 
quantity  of  blood  could  not  be  replaced  out  of  less  than  three 
or  four  times  the  quantity  of  lymph  and  chyle. 

Absorption  by  the  Lacteal  Vessels. 

During  the  passage  of  the  chyme  along  the  whole  tract  of 
the  intestinal  canal,  its  completely  digested  parts  are  absorbed 
by  the  bloodvessels  and  lacteals  distributed  in  the  mucous 
membrane.  The  bloodvessels  appear  to  absorb  chiefly  the 
dissolve^  portions  of  the  fqod,  and  these,  including  especially 
the  albuminous  and  saccharine,  they  imbibe  without  choice ; 
whateyer  can  mix  with  the  blood  passes  into  the  vessels,  as 


ABSORPTION     BY     LYMPHATICS.  291 

will  be  presently  described.  But  the  lacteals  appear  to  absorb 
only  certain  constituents  of  the  food,  including  particularly 
the  fatty  portions.  The  absorption  by  both  sets  of  vessels  is 
carried  on  most  actively,  but  not  exclusively,  in  the  villi  of 
the  small  intestine ;  for  in  these  minute  processes,  both  the 
capillary  bloodvessels  and  the  lacteals  are  brought  almost  into 
contact  with  the  intestinal  contents. 

It  has  been  already  stated  that  the  villi  of  the  small  intestine 
(Figs.  81  and  82),  are  minute  vascular  processes  of  mucous 
membrane,  each  containing  a  delicate  network  of  bloodvessels 
and  one  or  more  lacteals,  and  are  invested  by  a  sheath  of  cylin- 
drical epithelium.  In  the  interspaces  of  the  mucous  mem- 
brane between  the  villi,  as  well  as  over  all  the  rest  of  the 
intestinal  canal,  the  lacteals  and  bloodvessels  are  also  densely 
distributed  in  a  close  network,  the  lacteals,  however,  being 
more  sparingly  supplied  to  the  large  than  to  the  small  in- 
testine. 

There  seems  to  be  no  doubt  that  absorption  of  fatty  matters 
during  digestion,  from  the  contents  of  the  intestines,  is  effected 
chiefly  by  the  epithelial  cells  which  line  the  intestinal  tract, 
and  especially  by  those  which  clothe  the  surface  of  the  villi 
(Fig.  81).  From  these  epithelial  cells,  again,  the  fatty  parti- 
cles are  passed  on  into  the  interior  of  the  lacteal  vessels  (Figs. 
81  and  82),  but  how  they  pass,  and  what  laws  govern  their  so 
doing,  are  not  at  present  exactly  known. 

It  is  probable  that  the  process  of  absorption  by  the  epithe- 
lial cells,  is  assisted  by  the  pressure  exercised  on  the  contents 
of  the  intestines  by  their  contractile  walls ;  and  that  the  ab- 
sorption of  fatty  particles  is  also  facilitated  by  the  presence  of 
the  bile,  the  pancreatic  and  intestinal  secretions,  which  moisten 
the  absorbing  surface.  For  it  has  been  found  by  experiment, 
that  the  passage  of  oil  through  an  animal  membrane  is  made 
much  easier  when  the  latter  is  impregnated  with  an  alkaline 
fluid. 

Absorption  by  the  Lymphatic  Vessels. 

The  real  source  of  the  lymph,  and  the  mode  in  which  its 
absorption  is  effected  by  the  lymphatic  vessels,  were  long  mat- 
ters of  discussion.  But  the  problem  has  been  much  simplified 
by  more  accurate  knowledge  of  the  anatomical  relations  of  the 
lymphatic  capillaries.  It  is  most  probable  that  the  lymph  is 
derived,  in  great  part,  from  the  liquor  snnguinis,  which,  as  be- 
fore remarked,  is  always  exuding  from  the  blood-capillaries 
into  the  interstices  of  the  tissues  in  which  they  lie;  and 
changes  in  the  character  of  the  lymph  correspond  very  closely 
with  changes  in  the  character  of  either  the  whole  mass  of 


292  ABSORPTION. 

blood,  or  of  that  in  the  vessels  of  the  part  from  which  the 
lymph  is  examined.  Thus  Herbst  found  that  the  coagula- 
bility of  the  lymph  is  directly  proportionate  to  that  of  the 
blood ;  and  that  when  fluids  are  injected  into  the  bloodvessels 
in  sufficient  quantity  to  distend  them,  the  injected  substance 
may  be  almost  directly  afterwards  found  in  the  lymphatics. 

It  is  not  improbable,  however,  that  some  other  matters  than 
those  originally  contained  in  the  exuded  liquor  sanguinis  may 
find  their  way  with  it  into  the  lymphatic  vessels.  Parts  which, 
having  entered  into  the  composition  of  a  tissue,  and,  having 
fulfilled  their  purpose,  require  to  be  removed,  may  not  be 
altogether  excrementitious,  but  may  admit  of  being  reorganized 
and  adapted  again  for  nutrition  ;  and  these  may  be  absorbed 
by  the  lymphatics,  and  elaborated  with  the  other  contents  of 
the  lymph  in  passing  through  the  glands. 

Lymph- Hearts. — In  reptiles  and  some  birds,  an  important 
auxiliary  to  the  movement  of  the  lymph  and  chyle  is  supplied 
in  certain  muscular  sacs,  named  lymph-hearts  (Fig.  100),  and 
Mr.  Wharton  Jones  has  lately  shown  that  the  caudal  heart 
of  the  eel  is  a  lymph-heart  also.  The  number  and  position  of 

FIG.  100. 


Lymphatic  heart  (9  lines  long,  4  lines  broad)  of  a  large  species  of  serpent,  the 
Python  bivittatus  (after  E.  Weber).  4.  The  external  cellular  coat.  5.  The  thick 
muscular  coat.  Four  muscular  columns  run  across  its  cavity,  which  communicates 
with  three  lymphatics  (1— only  one  is  seen  here),  with  two  veins  (2,2).  6.  The 
smooth  lining  membrane  of  the  cavity.  7.  A  small  appendage,  or  auricle,  the  cavity 
of  which  is  continuous  with  that  of  the  rjst  of  the  organ. 

these  organs  vary.  In  frogs  and  toads  there  are  usually  four, 
two  anterior  and  two  posterior ;  in  the  frog,  the  posterior  lymph- 
heart  on  each  side  is  situated  in  the  ischiatic  region,  just  be- 
neath the  skin ;  the  anterior  lies  deeper,  just  over  the  transverse 
process  of  the  third  vertebra.  Into  each  of  these  cavities 
several  lymphatics  open,  the  orifices  of  the  vessels  being  guarded 


ABSORPTION    BY     BLOODVESSELS.  293 

by  valves,  which  prevent  the  retrograde  passage  of  the  lymph. 
From  each  heart  a  single  vein  proceeds  and  conveys  the  lymph 
directly  into  the  venous  system.  In  the  frog,  the  inferior  lym- 
phatic heart,  on  each  side,  pours  its  lymph  into  a  branch  of 
the  ischiatic  vein  ;  by  the  superior,  the  lymph  is  forced  into  a 
branch  of  the  jugular  vein,  which  issues  from  its  anterior  sur- 
face, and  which  becomes  turgid  each  time  that  the  sac  contracts. 
Blood  is  prevented  from  passing  from  the  vein  into  the  lym- 
phatic heart  by  a  valve  at  its  orifice. 

The  muscular  coat  of  these  hearts  is  of  variable  thickness ; 
in  some  cases  it  can  only  be  discovered  by  means  of  the  micro- 
scope ;  but  in  every  case  it  is  composed  of  transversely-striated 
fibres.  The  contractions  of  the  hearts  are  rhythmical,  occur- 
ring about  sixty  times  in  a  minute,  slowly,  and,  in  comparison 
with  those  of  the  blood-hearts,  feebly.  The  pulsations  of  the 
cervical  pair  are  not  always  synchronous  with  those  of  the 
pair  in  the  ischiatic  region,  and  even  the  corresponding  sacs  of 
opposite  sides  are  not  always  synchronous  in  their  action. 

Unlike  the  contractions  of  the  blood-heart,  those  of  the 
lymph-heart  appear  to  be  directly  dependent  upon  a  certain 
limited  portion  of  the  spinal  cord.  For  Volkmann  found  that 
so  long  as  the  portion  of  spinal  cord  corresponding  to  the  third 
vertebra  of  the  frog  was  uninjured,  the  cervical  pair  of  lym- 
phatic hearts  continued  pulsating  after  all  the  rest  of  the  spinal 
cord  and  the  brain  was  destroyed ;  while  destruction  of  this 
portion,  even  though  all  other  parts  of  the  nervous  centres 
were  uninjured,  instantly  arrested  the  heart's  movements.  The 
posterior  or  ischiatic  pair  of  lymph-hearts  were  found  to  be 
governed,  in  like  manner,  by  the  portion  of  spinal  cord  cor- 
responding to  the  eighth  vertebra.  Division  of  the  posterior 
spinal  roots  did  not  arrest  the  movements ;  but  division  of  the 
anterior  roots  caused  them  to  cease  at  once. 

Absorption  by  Bloodvessels. 

The  process  thus  named  is  that  which  has  been  commonly 
called  absorption  by  the  veins;  but  the  term  here  employed 
seems  preferable,  since,  though  the  materials  absorbed  are 
commonly  found  in  the  veins,  this  is  only  because  they  are 
carried  into  them  with  the  circulating  blood,  after  being  ab- 
sorbed by  all  the  bloodvessels  (but  chiefly  by  the  capillaries) 
with  which  they  were  placed  in  contact.  There  is  nothing  in 
the  mode  of  absorption  by  bloodvessels,  or  in  the  structure  of 
veins,  which  can  make  the  latter  more  active  than  arteries  of 
the  same  size,  or  so  active  as  the  capillaries,  in  the  process. 

In  the  absorption  by  the  lymphatics  or  lacteal  vessels  just 

25 


294 


ABSORPTION, 


FIG.  101. 


described,  there  appears  something  like  the  exercise  of  choice 
in  the  materials  admitted  into  them.  But  the  absorption  by 
bloodvessels  presents  no  such  appearance  of  selection  of  ma- 
terials; rather,  it  appears,  that  every  substance,  whether 
gaseous,  liquid,  or  a  soluble  or  minutely  divided  solid,  may 
be  absorbed  by  the  bloodvessels,  provided  it  is  capable  of  per- 
meating their  walls,  and  of  mixing  with  the  blood  ;  and  that 
of  all  such  substances,  the  mode  and  measure  of  absorption  are 
determined  solely  by  their  physical  or  chemical  properties  and 
conditions,  and  by  those  of  the  blood  and  the  walls  of  the 
bloodvessels. 

The  phenomena  are,  indeed,  exactly  comparable  to  that 
passage  of  fluids  through  membrane,  which  occurs  quite  inde- 
pendently of  vital  conditions,  and  the  earliest  and  best  scien- 
tific investigation  of  which  was  made  by  Dutrochet.  The  in- 
strument which  he  employed  in  his  experiments 
was  named  an  endosmometer.  It  may  consist  of 
a  graduated  tube  expanded  into  an  open-mouthed 
bell  at  one  end,  over  which  a  portion  of  mem- 
brane is  tied  (Fig.  101).  If  now  the  bell  be 
filled  with  a  solution  of  a  salt,  say  chloride  of 
sodium,  and  be  immersed  in  water,  the  water 
will  pass  into  the  solution,  and  part  of  the  salt 
will  pass  out  into  the  water ;  the  water  will  pass 
into  the  solution  much  more  rapidly  than  the 
salt  will  pass  out  into  the  water,  and  the  diluted 
solution  will  rise  in  the  tube.  To  this  passage  of 
fluids  through  membrane  the  term  Osmosis  is  ap- 
plied. 

The  nature  of  the  membrane  used  as  a  septum, 
and  its  affinity  for  the  fluids  subjected  to  ex- 
periment, have  an  important  influence,  as  might 
be  anticipated,  on  the  rapidity  and  duration  of 
the  osmotic  current.  Thus,  if  a  piece  of  ordinary 
bladder  be  used  as  the  septum  between  water  and 
alcohol,  the  current  is  almost  solely  from  the 
water  to  the  alcohol,  on  account  of  the  much 
greater  affinity  of  water  for  this  kind  of  mem- 
brane ;  while,  on  the  other  hand,  in  the  case  of  a  membrane  of 
caoutchouc,  the  alcohol,  from  its  greater  affinity  for  this  sub- 
stance, would  pass  freely  into  the  water. 

Various  opinions  have  been  advanced  in  regard  to  the  na- 
ture of  the  force  by  which  fluids  of  different  chemical  compo- 
sition thus  tend  to  mix  through  an  intervening  membrane. 
According  to  some,  this  power  is  the  result  of  the  different  de- 
grees of  capillary  attraction  exerted  by  the  pores  of  the  mem- 


COLLOIDS     AND    CRYSTALLOIDS.  295 

brane  upon  the  two  fluids.  Prof.  Graham,  however,  believes 
that  the  passage  or  osmose  of  water  through  membrane  may 
be  explained  by  supposing  that  it  combines  with  the  membra- 
nous septum,  which  thus  becomes  hydrated,  and  that  on  reach- 
ing the  other  side  it  partly  leaves  the  membrane,  which  thus 
becomes  to  a  certain  degree  dehydrated.  For  example,  a 
membrane  such  as  that  used  in  the  endosmometer,  is  hydrated 
to  a  higher  degree  if  placed  in  pure  water  than  in  a  neutral 
saline  solution.  Hence,  in  the  case  of  the  endosmometer  filled 
with  the  saline  solution  and  placed  in  water,  the  equilibrium 
of  hydration  is  different  on  the  two  sides ;  the  outer  surface 
being  in  contact  with  pure  water  tends  to  hydrate  itself  in  a 
higher  degree  than  the  inner  surface  does.  "  When  the  full 
hydration  of  the  outer  surface  extends  through  the  thickness 
of  the  membrane,  and  reaches  the  inner  surface,  it  there  re- 
ceives a  check.  The  degree  of  hydration  is  lowered,  and 
water  must  be  given  up  by  the  inner  layer  of  the  membrane." 
Thus  the  osmose  or  current  of  water  through  the  membrane  is 
caused.  The  passage  outwards  of  the  saline  solution,  on  the 
other  hand,  is  not  due,  probably,  to  any  actual  fluid  current ; 
but  to  a  solution  of  the  salt  in  successive  layers  of  the  water 
contained  in  the  pores  of  the  membrane,  until  it  reaches  the 
outer  surface  and  diffuses  in  the  water  there  situate. 

Thus,  "  the  water  movement  in  osmose  is  an  affair  of  hydra- 
tion and  of  dehydration  in  the  substance  of  the  membrane  or 
other  colloid  septum,  and  the  diffusion  of  the  saline  solution 
placed  within  the  osmometer  has  little  or  nothing  to  do  with 
the  osmotic  result,  otherwise  than  as  it  affects  the  state  of  hy- 
dration of  the  septum." 

Prof.  Graham  has  classed  various  substances  according  to 
the  degree  in  which  they  possess  this  property  of  passing,  when 
in  a  state  of  solution  in  water,  through  membrane  ;  those  which 
pass  freely  being  termed  crystalloids,  and  those  which  pass  with 
difficulty,  colloids. 

This  distinction,  however,  between  colloids  and  crystalloids, 
which  is  made  the  basis  of  their  classification,  is  by  no  means 
the  only  difference  between  them.  The  colloids,  besides  the 
absence  of  power  to  assume  a  crystalline  form,  are  character- 
ized by  their  inertness  as  acids  or  bases,  and  feebleness  in  all 
ordinary  chemical  relations.  Examples  of  them  are  found  in 
albumen,  gelatin,  starch,  hydrated  alumina,  hydrated  silicic 
acid,  &c. ;  while  the  crystalloids  are  characterized  by  qualities 
the  reverse  of  those  just  mentioned  as  belonging  to  colloids. 
Alcohol,  sugar,  and  ordinary  saline  substances  are  examples 
of  crystalloids. 

Absorption  by  bloodvessels  is  the  consequence  of  their  walls 


296  ABSORPTION. 

being,  like  the  membranous  septum  of  the  eudosmometer,  por- 
ous and  capable  of  imbibing  fluids,  and  of  the  blood  being  so 
composed  that  most  fluids  will  mingle  with  it.  The  process  of 
absorption,  in  an  instructive,  though  very  imperfect  degree, 
may  be  observed  in  any  portion  of  vascular  tissue  removed 
from  the  body.  If  such  a  one  be  placed  in  a  vessel  of  water, 
it  will  shortly  swell,  and  become  heavier  and  moister,  through 
the  quantity  of  water  imbibed  or  soaked  into  it;  and  if  now, 
the  blood  contained  in  any  of  its  vessels  be  let  out,  it  will  be 
found  diluted  with  water,  which  has  been  absorbed  by  the 
bloodvessels  and  mingled  with  the  blood.  The  water  round 
the  piece  of  tissue  also  will  become  bloodstained ;  and  if  all 
be  kept  at  perfect  rest,  the  stain  derived  from  the  solution  of 
the  coloring  matter  of  the  blood  (together  with  which  chemistry 
would  detect  some  of  the  albumen  and  other  parts  of  the  liquor 
sanguinis)  will  spread  more  widely  every  day.  The  same  will 
happen  if  the  piece  of  tissue  be  placed  in  a  saline  solution  in- 
stead of  water,  or  in  a  solution  of  coloring  or  odorous  matter, 
either  of  which  will  give  their  tinge  or  smell  to  the  blood,  and 
receive,  in  exchange,  the  color  of  the  blood. 

Even  so  simple  an  experiment  will  illustrate  the  absorption 
by  bloodvessels  during  life ;  the  process  it  shows  is  imitated, 
but  with  these  differences :  that,  during  life,  as  soon  as  water 
or  any  other  substance  is  admitted  into  the  blood,  it  is  carried 
from  the  place  at  which  it  was  absorbed  into  the  general  cur- 
rent of  the  circulation,  and  that  the  coloring  matter  of  the 
blood  is  not  dissolved  so  as  to  ooze  out  of  the  bloodvessels  into 
the  fluid  which  they  are  absorbing. 

The  absorption  of  gases  by  the  blood  may  be  thus  simply 
imitated.  If  venous  blood  be  suspended  in  a  moist  bladder  in 
the  air,  its  surface  will  be  reddened  by  the  contact  of  oxygen, 
which  is  first  dissolved  in  the  fluid  that  moistens  the  bladder, 
and  is  then  carried  in  the  fluid  to  the  surface  of  the  blood : 
while,  on  the  other  hand,  watery  vapor  and  carbonic  acid  will 
pass  through  the  membrane,  and  be  exhaled  into  the  air. 

In  all  these  cases  alike  there  is  a  mutual  interchange  be- 
tween the  substances  ;  while  the  blood  is  receiving  water,  it  is 
giving  out  its  coloring  matter  and  other  constituents :  or,  while 
it  is  receiving  oxygen,  it  is  giving  out  carbonic  acid  and  water; 
so  that,  at  the  end  of  the  experiment,  the  two  substances  em- 
ployed in  it  are  mixed ;  and  if,  instead  of  a  piece  of  tissue,  one 
had  taken  a  single  bloodvessel  full  of  blood  and  placed  it  in 
the  water,  both  blood  and  water  would,  after  a  time,  have  been 
found  both  inside  and  outside  the  vessel.  In  such  a  case,  more- 
over, if  one  were  to  determine  accurately  the  quantity  of  water 
that  passed  to  the  blood,  and  of  blood -that  passed  to  the  water, 


RAPIDITY    OF    ABSORPTION.  297 

it  would  be  found  that  the  former  was  always  greater  than  the 
latter.  And  so  with  other  substances ;  it  almost  always  hap- 
pens, that  if  the  two  liquids  placed  on  opposite  sides  of  a  mem- 
brane be  of  different  densities  or  specific  gravities,  a  larger 
quantity  of  the  less  dense  fluid  passes  into  the  more  dense,  than 
of  the  latter  into  the  former. 

The  rapidity  with  which  matters  may  be  absorbed  from  the 
stomach  probably  by  the  bloodvessels  chiefly,  and  diffused 
through  the  textures  of  the  body,  may  be  gathered  from  the 
history  of  some  experiments  by  Dr.  Bence  Jones.  From  these 
it  appears  that  even  in  a  quarter  of  an  hour,  after  being  given 
on  an  empty  stomach,  chloride  of  lithium  maybe  diffused  into 
all  the  vascular  textures  of  the  body,  and  into  some  of  the  non- 
vascular,  as  the  cartilage  of  the  hip-joint,  as  well  as  into  the 
aqueous  humor  of  the  eye.  Into  the  outer  part  of  the  crystal- 
line lens  it  may  pass  after  a  time,  varying  from  half  an  hour 
to  an  hour  and  a  half.  Carbonate  of  lithia,  when  taken  in 
five  or  ten-grain  doses  on  an  empty  stomach,  may  be  detected 
in  the  urine  in  5  or  10  minutes;  or,  if  the  stomach  be  full  at 
the  time  of  taking  the  dose,  in  20  minutes.  It  may  sometimes 
be  detected  in  the  urine,  moreover,  for  six,  seven,  or  even 
eight  days. 

Some  experiments  on  the  absorption  of  various  mineral  and 
vegetable  poisons,  by  Mr.  Savory,  have  brought  to  light  the 
singular  fact,  that,  in  some  cases,  absorption  takes  place  more 
rapidly  from  the  rectum  than  from  the  stomach.  Strychnia, 
for  example,  when  in  solution,  produces  its  poisonous  effects 
much  more  speedily  when  introduced  into  the  rectum  than 
into  the  stomach.  When  introduced  in  the  solid  form,  how- 
ever, it  is  absorbed  more  rapidly  from  the  stomach  than  from 
the  rectum,  doubtless  because  of  the  greater  solvent  property 
of  the  secretion  of  the  former  than  of  that  of  the  latter. 

With  regard  to  the  degree  of  absorption  by  living  blood- 
vessels, much  depends  on  the  facility  with  which  the  substance 
to  be  absorbed  can  penetrate  the  membrane  or  tissue  which 
lies  between  it  and  the  bloodvessels ;  for,  naturally,  the  blood- 
vessels are  not  bare  to  absorb.  Thus  absorption  will  hardly 
take  place  through  the  epidermis,  but  is  quick  when  the  epi- 
dermis is  removed,  and  the  same  vessels  are  covered  with  only 
the  surface  of  the  cutis,  or  with  granulations.  In  general,  the 
absorption  through  membranes  is  in  an  inverse  proportion  to 
the  thickness  of  their  epithelia ;  so  Miiller  found  the  urinary 
bladder  of  a  frog  traversed  in  less  than  a  second  ;  and  the  ab- 
sorption of  poisons  by  the  stomach  or  lungs  appears  sometimes 
accomplished  in  an  immeasurably  small  time. 

The  substance  to  be  absorbed  must,  as  a  general  rule,  be  in 


298  ABSOKPTION. 

the  liquid  or  gaseous  state,  or,  if  a  solid,  must  be  soluble  in  the 
fluids  with  which  it  is  brought  in  contact.  Hence  the  marks 
of  tattooing,  and  the  discoloration  produced  by  nitrate  of  silver 
taken  internally,  remain.  Mercury  may  be  absorbed  even  in 
the  metallic  state ;  and  in  that  state  may  pass  into  and  remain 
in  the  bloodvessels,  or  be  deposited  from  them  (Oesterlen) ; 
and  such  substances  as  exceedingly  finely-divided  charcoal, 
when  taken  into  the  alimentary  canal,  have  been  found  in  the 
raesenteric  veins  (Oesterlen)  ;  the  insoluble  materials  of  oint- 
ments may  also  be  rubbed  into  the  bloodvessels ;  but  there  are 
no  facts  to  determine  how  these  various  substances  effect  their 
passage.  Oil,  minutely  divided,  as  in  an  emulsion,  will  pass 
slowly  into  bloodvessels,  as  it  will  through  a  filter  moistened 
with  water  (Vogel) ;  and,  without  doubt,  fatty  matters  find 
their  way  into  the  bloodvessels  as  well  as  the  lymphvessels  of 
the  intestinal  canal,  although  the  latter  seem  to  be  specially 
intended  for  their  absorption. 

As  in  the  experiments  before  referred  to,  the  less  dense  the 
fluid  to  be  absorbed,  the  more  speedy,  as  a  general  rule,  is  its 
absorption  by  the  living  bloodvessels.  Hence  the  rapid  ab- 
sorption of  water  from  the  stomach ;  also  of  weak  saline  solu- 
tions ;  but  with  strong  solutions,  there  appears  less  absorption 
into,  than  effusion  from,  the  bloodvessels. 

The  absorption  is  the  less  rapid  the  fuller  and  tenser  the 
bloodvessels  are ;  and  the  tension  may  be  so  great  as  to  hinder 
altogether  the  entrance  of  more  fluid.  Thus,  Magendie  found 
that  when  he  injected  water  into  a  dog's  veins  to  repletion, 
poison  was  absorbed  very  slowly ;  but  when  he  diminished  the 
tension  of  the  vessels  by  bleeding,  the  poison  acted  quickly. 
So,  when  cupping-glasses  are  placed  over  a  poisoned  wound, 
they  retard  the  absorption  of  the  poison,  not  only  by  diminish- 
ing the  velocity  of  the  circulation  in  the  part,  but  by  filling  all 
its  vessels  too  full  to  admit  more. 

On  the  same  ground,  absorption  is  the  quicker  the  more 
rapid  the  circulation  of  the  blood ;  not  because  the  fluid  to  be 
absorbed  is  more  quickly  imbibed  into  the  tissues,  or  mingled 
with  the  blood,  but  because  as  fast  as  it  enters  the  blood,  it  is 
carried  away  from  the  part,  and  the  blood,  being  constantly 
renewed,  is  constantly  as  fit  as  at  the  first  for  the  reception  of 
the  substance  to  be  absorbed. 


NUTRITION.  299 


CHAPTER  XI. 

NUTRITION   AND    GROWTH. 

NUTRITION  or  nutritive  assimilation  is  that  modification  of 
the  formative  process  peculiar  to  living  bodies  by  which  tissues 
and  organs  already  formed  maintain  their  integrity.  By  the 
incorporation  of  fresh  nutritive  principles  into  their  substance, 
the  loss  consequent  on  the  waste  and  natural  decay  of  the  com- 
ponent particles  of  the  tissues  is  repaired  ;  and  each  elementary 
particle  seems  to  have  the  power  not  only  of  attracting  ma- 
terials from  the  blood,  but  of  causing  them  to  assume  its  struc- 
ture, and  participate  in  its  vital  properties. 

The  relations  between  development  and  growth  have  been 
already  stated  (Chap.  I) ;  under  the  head  of  Nutrition  will  be 
now  considered  the  process  by  which  parts  are  maintained  in 
the  same  general  conditions  of  form,  size,  and  composition, 
which  they  have  already,  by  development  and  growth,  at- 
tained;  and  this,  notwithstanding  continual  changes  in  their 
component  particles.  It  is  by  this  process  that  an  adult  per- 
son, in  health,  is  maintained,  through  a  series  of  some  years, 
with  the  same  general  outline  of  features,  the  same  size  and 
form,  and  perhaps  even  the  same  weight ;  although,  during  all 
this  time,  the  several  portions  of  his  body  are  continually 
changing:  their  particles  decaying  and  being  removed,  and 
then  replaced  by  the  formation  of  new  ones,  which,  in  their 
turn,  also  die  and  pass  away.  Neither  is  it  only  a  general 
similarity  of  the  whole  body  which  is  thus  maintained.  Every 
organ  or  part  of  the  body,  as  much  as  the  whole,  exactly  main- 
tains its  form  and  composition,  as  the  issue  of  the  changes  con- 
tinually taking  place  among  its  particles. 

The  change  of  component  particles,  in  which  the  nutrition 
of  organs  consists,  is  most  evidently  shown  when,  in  growth, 
they  maintain  their  form  and  other  general  characters,  but 
increase  in  size.  When,  for  example,  a  long  bone  increases 
in  circumference,  and  in  the  thickness  of  its  walls,  while,  at 
the  same  time,  its  medullary  cavity  enlarges,  it  can  only  be 
by  the  addition  of  materials  to  its  exterior,  and  a  coincident 
removal  of  them  from  the  interior  of  its  wall ;  and  so  it  must 
be  with  the  growth  of  even  the  minutest  portions  of  a  tissue. 
And  that  a  similar  change  of  particles  takes  place,  even  while 


300  NUTRITION. 

parts  retain  a  perfect  uniformity,  may  be  proved,  if  it  can  be 
shown  that  all  the  parts  of  the  body  are  subject  to  waste  and 
impairment. 

In  many  parts,  the  removal  of  particles  is  evident.  Thus, 
as  will  be  shown  when  speaking  of  secretion,  the  elementary 
structures  composing  glands  are  the  parts  of  which  the  secre- 
tions are  composed :  each  gland  is  constantly  casting  off  its 
cells,  or  their  contents,  in  the  secretion  which  it  forms :  yet 
each  gland  maintains  its  size  and  proper  composition,  because 
for  every  cell  cast  off  a  new  one  is  produced.  So  also  the 
epidermis  and  all  such  tissues  are  maintained.  In  the  mus- 
cles, it  seems  nearly  certain,  that  each  act  of  contraction  is 
accompanied  with  a  change  in  the  composition  of  the  con- 
tracting tissue,  although  the  change  from  this  cause  is  less 
rapid  and  extensive  than  was  once  supposed.  Thence,  the 
development  of  heat  in  acting  muscles,  and  then  the  discharge 
of  urea,  carbonic  acid,  and  water — the  ordinary  products  of 
the  decomposition  of  the  animal  tissues — which  follows  all 
active  muscular  exercise.  Indeed,  the  researches  of  Helm- 
holtz  almost  demonstrate  the  chemical  change  that  muscles 
undergo  after  long-repeated  contractions;  yet  the  muscles 
retain  their  structure  and  composition,  because  the  particles 
thus  changed  are  replaced  by  new  ones  resembling  those  which 
preceded  them.  So  again,  the  increase  of  alkaline  phosphates 
discharged  with  the  urine  after  great  mental  exertion,  seems 
to  prove  that  the  various  acts  of  the  nervous  system  are  at- 
tended with  change  in  the  composition  of  the  nervous  tissue ; 
yet  the  condition  of  that  tissue  is  maintained.  In  short,  for 
every  tissue  there  is  sufficient  evidence  of  impairment  in  the 
discharge  of  its  functions :  without  such  change,  the  produc- 
tion or  resistance  of  physical  force  is  hardly  conceivable :  and 
the  proof  as  well  as  the  purpose  of  the  nutritive  process  ap- 
pears in  the  repair  or  replacement  of  the  changed  particles ; 
so  that,  notwithstanding  its  losses,  each  tissue  is  maintained 
unchanged. 

But  besides  the  impairment  and  change  of  composition  to 
which  all  parts  are  subject  in  the  discharge  of  their  natural 
functions,  an  amount  of  impairment  which  will  be  in  direct 
proportion  to  their  activity,  they  are  all  liable  to  decay  and 
degeneration  of  their  particles,  even  while  their  natural  actions 
are  not  called  forth.  It  may  be  proved,  as  Dr.  Carpenter  first 
clearly  showed,  that  every  particle  of  the  body  is  formed  for  a 
certain  period  of  existence  in  the  ordinary  condition  of  active 
life ;  at  the  end  of  which  period,  if  not  previously  destroyed  by 
outward  force  or  exercise,  it  degenerates  and  is  absorbed,  or 
dies  and  is  cast  out. 


NUTRITION     OF     HAIR. 


301 


The  simplest  examples  that  can  be  adduced  of  this  are  in 
the  hair  and  teeth ;  and  it  may  be  observed,  that,  in  the  pro- 
cess which  will  now  be  described,  all  the  great  features  of  the 
process  of  nutrition  seem  to  be  represented.1 

An  eyelash  which  naturally  falls,  or  which  can  be  drawn 
out  without  pain,  is  one  that  has  lived  its  natural  time,  and 
has  died,  and  been  separated  from  the  living  parts.  In  its 
bulb  such  a  one  will  be  found  different  from  those  that  are 


Intended  to  represent  the  changes  undergone  by  a  hair  towards  the  close  of  its 
period  of  existence.  At  A,  its  activity  of  growth  is  diminishing,  as  shown  by  the 
small  quantity  of  pigment  contained  in  the  cells  of  the  pulp,  and  by  the  interrupted 
line  of  dark  medullary  substance.  At  B,  provision  is  being  made  for  the  formation 
of  a  new  hair,  by  the  growth  of  a  new  pulp  connected  with  the  pulp  or  capsule  of 
the  old  hair.  c.  A  hair  at  the  end  of  its  period  of  life,  deprived  of  its  sheath  and  of 
the  mass  of  cells  composing  the  pulp  of  a  living  hair. 

still  living  in  any  period  of  their  age.  In  the  early  period  of 
the  growth  of  a  dark  eyelash,  the  medullary  substance  appears 
like  an  interior  cylinder  of  darker  granular  substance,  con- 


1  These  and  other  instances  are  related  more  in  detail  in  Mr. 
Paget's  Lectures  on  Surgical  Pathology,  from  which  this  chapter  was 
originally  written. 

26 


302  NUTRITION. 

tinned  down  to  the  deepest  part,  where  the  hair  enlarges  to 
form  the  bulb.  This  enlargement,  which  is  of  nearly  cup- 
like  form,  appears  to  depend  on  the  accumulation  of  nucleated 
cells,  whose  nuclei,  according  to  their  position,  are  either,  by 
narrowing  and  elongation,  to  form  the  fibrous  substance  of  the 
outer  part  of  the  growing  and  further  protruding  hair,  or  are 
to  be  transformed  into  the  granular  matter  of  its  medullary 
portion.  At  the  time  of  early  and  most  active  growth,  all  the 
cells  and  nuclei  contain  abundant  pigment-matter,  and  the 
whole  bulb  looks  nearly  black.  The  sources  of  the  material 
out  of  which  the  cells  form  themselves  are  at  least  two ;  the 
inner  surface  of  the  sheath  or  capsule,  which  dips  into  the 
skin,  enveloping  the  hair,  and  the  surface  of  a  vascular  pulp 
which  fits  in  a  conical  cavity  in  the  bottom  of  the  hair-bulb. 

Such  is  the  state  of  parts  so  long  as  the  growing  hair  is  all  dark. 
But  as  the  hair  approaches  the  end  of  its  existence,  instead  of 
the  almost  sudden  enlargement  at  its  bulb,  it  only  swells  a 
little,  and  then  tapers  nearly  to  a  point ;  the  conical  cavity  in 
its  base  is  contracted ;  and  the  cells  produced  on  the  inner 
surface  of  the  capsule  contain  no  pigment.  Still,  for  some 
time,  it  continues  thus  to  live  and  grow ;  and  the  vigor  of  the 
pulp  lasts  rather  longer  than  that  of  the  sheath  or  capsule,  for 
it  continues  to  produce  pigment-matter  for  the  medullary  sub- 
stance of  the  hair  after  the  cortical  substance  has  become 
white.  Thus  the  column  of  dark  medullary  substance  appears 
paler  and  more  slender,  and  perhaps  interrupted,  down  to  the 
point  of  the  conical  pulp,  which,  though  smaller,  is  still  dis- 
tinct, because  of  the  pigment-cells  covering  its  surface. 

At  length  the  pulp  can  be  no  longer  discerned,  and  un- 
colored  cells  are  alone  produced,  and  maintain  the  latest 
growth  of  the  hair.  With  these  it  appears  to  grow  yet  some 
further  distance ;  for  traces  of  the  elongation  of  their  nuclei 
into  fibres  appear  in  lines  running  from  the  inner  surface  of 
the  capsule  inwards  and  along  the  surface  of  the  hair ;  and  the 
column  of  dark  medullary  substance  ceases  at  some  distance 
above  the  lower  end  of  the  contracted  hair-bulb.  The  end  of 
all  is  the  complete  closure  of  the  conical  cavity  in  which  the 
hair-pulp  was  lodged,  the  cessation  of  the  production  of  new 
cells  from  the  inner  surface  of  the  capsule,  and  the  detach- 
ment of  the  hair,  which,  as  a  dead  part,  is  separated  and  falls. 

Such  is  the  life  of  a  hair,  and  such  its  death ;  which  death 
is  spontaneous,  independent  of  exercise,  or  of  any  mechanical 
external  force — the  natural  termination  of  a  certain  period  of 
life.  Yet,  before  the  hair  dies,  provision  is  made  for  its  suc- 
cessor :  for  when  its  growth  is  failing,  there  appears  below  its 
base  a  dark  spot,  the  germ  or  young  pulp  of  the  new  hair 


MAINTENANCE     BY     NUTRITION. 


303 


FIG.  103. 


covered  with  cells  containing  pigment,  and  often  connected  by 
a  series  of  pigment-cells  with  the  old  pulp  or  capsule  (Fig. 
102,  B). 

Probably  there  is  an  intimate  analogy  between  the  process 
of  successive  life  and  death,  and  life  communicated  to  a  suc- 
cessor, which  is  here  shown,  and  that  which  constitutes  the 
ordinary  nutrition  of  a  part.  It  may  be  objected,  that  the 
death  and  casting  out  of  the  hair  cannot  be  imitated  in  inter- 
nal parts ;  therefore,  for  an  example  in  which  the  assumed 
absorption  of  the  worn-out  or  degenerate  internal  particles  is 
imitated  in  larger  organs  at  the  end  of  their  appointed  period 
of  life,  the  instance  of  the  deciduous  or  milk-teeth  may  be 
adduced. 

Each  milk-tooth  is  developed  from  its  germ ;  and  in  the 
course  of  its  own  development,  separates  a  portion  of  itself  to 
be  the  germ  of  its  successor;  and 
each,  having  reached  its  perfec- 
tion, retains  for  a  time  its  perfect 
state,  and  still  lives,  though  it 
does  not  grow.  But  at  length, 
as  the  new  tooth  comes,  the  de- 
ciduous tooth  dies ;  or  rather  its 
crown  dies,  and  is  cast  out  like 
the  dead  hair,  while  its  fang, 
with  its  bony  sheathing,  and  vas- 
cular and  nervous  pulp,  degen- 
erates and  is  absorbed  (Fig.  103). 
The  degeneration  is  accompanied 
by  some  unknown  spontaneous 
decomposition  of  the  fang  ;  for  it 
could  not  be  absorbed  unless  it 
was  first  so  changed  as  to  be  solu- 
ble. And  it  is  degeneration,  not 
death,  which  precedes  its  re- 
moval; for  when  a  tooth-fang 

dies,  as  that  of  the  second  tooth  does  in  old  age,  then  it  is  not 
absorbed,  but  cast  out  entire,  as  a  dead  part. 

Such,  or  generally  such,  it  seems  almost  certain,  is  the  pro- 
cess of  maintenance  by  nutrition ;  the  hair  and  teeth  may  be 
fairly  taken  as  types  of  what  occurs  in  other  parts,  for  they 
are  parts  of  complex  organic  structure  and  composition,  and 
the  teeth-pulps,  which  are  absorbed  as  well  as  the  fangs,  are 
very  vascular  and  sensitive. 

Nor  are  they  the  only  instances  that  might  be  adduced. 
The  like  development,  persistence  for  a  time  in  the  perfect 
state,  death,  and  discharge,  appear  in  all  the  varieties  of  cuti- 


Section  of  a  portion  of  the  upper 
jaw  of  a  child,  showing  a  new  tooth 
in  process  of  formation,  the  fang  of 
the  corresponding  deciduous  tooth 
being  absorbed. 


304  NUTRITION. 

cles  and  glaDd-cells ;  and  in  the  epidermis,  as  in  the  teeth, 
there  is  evidence  of  decomposition  of  the  old  cells,  in  the  fact 
of  the  different  influence  which  acetic  acid  and  potash  exer- 
cise on  them  and  on  the  young  cells.  Seeing,  then,  that  the 
process  of  nutrition,  as  thus  displayed,  both  in  active  organs 
and  in  elementary  cells,  appears  in  these  respects  similar,  the 
general  conclusion  may  be  that,  in  nutrition,  the  ordinary 
course  of  each  complete  elementary  organ  in  the  body,  after 
the  attainment  of  its  perfect  state  by  development  and  growth, 
is  to  remain  in  that  state  for  a  time ;  then,  independently  of 
the  death  or  decay  of  the  whole  body,  and  in  some  measure, 
independently  of  its  own  exercise,  or  exposure  to  external 
violence,  to  die  or  to  degenerate  ;  and  then,  being  cast  out  or 
absorbed,  to  make  way  for  its  successor. 

It  appears,  moreover,  that  the  length  of  life  which  each  part 
is  to  enjoy  is  fixed  and  determinate,  though  in  some  degree 
subject  to  accidents  and  to  the  expenditure  of  life  in  exercise. 
It  is  not  likely  that  all  parts  are  made  to  last  a  certain  and 
equal  time,  and  then  all  need  to  be  changed.  The  bones,  for 
instance,  when  once  completely  formed,  must  last  longer  than 
the  muscles  and  other  softer  tissues.  But  when  we  see  that  the 
life  of  certain  parts  is  of  determined  length,  whether  they  be 
used  or  not,  we  may  assume,  from  analogy,  the  same  of 
nearly  all. 

Now,  the  deciduous  human  teeth  have  an  appointed  average 
duration  of  life.  So  have  the  deciduous  teeth  of  all  other 
animals;  and  in  all  the  numerous  instances  of  moulting,  shed- 
ding of  antlers,  of  desquamation,  change  of  plumage  in  birds, 
and  of  hair  in  Mammalia,  the  only  explanation  is  that  these 
organs  have  their  severally  appointed  times  of  living,  at  the 
ends  of  which  they  degenerate,  die,  are  cast  away,  and  in  due 
time  are  replaced  by  others,  which,  in  their  turn,  are  to  be  de- 
veloped to  perfection,  to  live  their  life  in  the  mature  state,  and 
in  their  turn  to  be  cast  off.  So  also,  in  some  elementary  struc- 
tures, we  may  discern  the  same  laws  of  determinate  period  of 
life,  death,  or  degeneration,  and  replacement.  They  are  evi- 
dent in  the  history  of  the  blood-corpuscles,  both  in  the  super- 
seding of  the  first  set  of  them  by  the  second  at  a  definite  period 
in  the  life  of  the  embryo,  and  in  the  replacement  of  those  that 
degenerate  by  others  new-formed  from  lymph -corpuscles.  (See 
p.  83.)  And  if  we  could  suppose  the  blood-corpuscles  grouped 
together  in  a  tissue  instead  of  floating,  we  might  have  in  the 
changes  they  present  an  image  of  the  nutrition  of  the  elements 
of  the  tissues. 

The  duration  of  life  in  each  particle  is,  however,  liable  to  be 
modified ;  especially  by  the  exercise  of  the  function  of  the 


PROCESS    OF    NUTRITION.  305 

part.  The  less  a  part  is  exercised  the  longer  do  its  component 
particles  appear  to  live :  the  more  active  its  functions  are,  the 
less  prolonged  is  the  existence  of  its  individual  particles.  So 
in  the  case  of  single  cells ;  if  the  general  development  of  the 
tadpole  be  retarded  by  keeping  it  in  a  cold,  dark  place,  and  if 
hereby  the  function  of  the  blood-corpuscles  be  slowly  and  im- 
perfectly discharged,  they  will  maintain  their  embryonic  state 
for  even  several  weeks  later  than  usual,  the  development  of 
the  second  set  of  corpuscles  will  be  proportionally  postponed, 
and  the  individual  life  of  the  corpuscles  of  the  first  set  will  be, 
by  the  same  time,  prolonged. 

Such  being  the  mode  in  which  the  necessity  for  the  process 
of  nutritive  maintenance  is  created,  such  the  sources  of  impair- 
ment and  waste  of  the  tissues,  the  next  consideration  may  be 
the  manner  in  which  the  perfect  state  of  a  part  is  maintained 
by  the  insertion  of  new  particles  in  the  place  of  those  that  are 
absorbed  or  cast  off. 

The  process  by  which  a  new  particle  is  formed  in  the  place  of 
the  old  one  is  probably  always  a  process  of  development ;  that 
is,  the  cell  or  fibre,  or  other  element  of  tissue,  passes  in  its 
formation  through  the  same  stages  of  development  as  those 
elements  of  the  same  tissue  did  which  were  first  formed  in  the 
embryo.  This  is  probable  from  the  analogy  of  the  hair,  the 
teeth,  the  epidermis,  and  all  the  tissues  that  can  be  observed : 
in  all,  the  process  of  repair  or  replacement  is  effected  through 
development  of  the  new  parts.  The  existence  of  nuclei  or  cyto- 
blasts  in  nearly  all  parts  that  are  the  seats  of  active  nutrition 
makes  the  same  probable.  For  these  nuclei,  such  as  are  seen 
so  abundant  in  strong,  active  muscles,  are  not  remnants  of  the 
embryonic  tissue,  but  germs  or  organs  of  power  for  new  forma- 
tion, and  their  abundance  often  appears  directly  proportionate 
to  the  activity  of  growth.  Thus,  they  are  always  abundant 
in  the  foetal  tissues,  and  those  of  the  young  animal ;  and  they 
are  peculiarly  numerous  in  the  muscles  and  the  brain,  and  their 
disappearance  from  a  part  in  which  they  usually  exist  is  a  sure 
accompaniment  and  sign  of  degeneration. 

A  difference  may  be  drawn  between  what  may  be  called 
nutritive  reproduction  and  nutritive  repetition.  The  former  is 
shown  in  the  case  of  the  human  teeth.  As  the  deciduous  tooth 
is  being  developed,  a  part  of  its  productive  capsule  is  detached, 
and  serves  as  a  germ  for  the  formation  of  the  second  tooth  •  in 
which  second  tooth,  therefore,  the  first  may  be  said  to  be  re? 
produced,  in  the  same  sonse  as  that  in  which  we  speak  of  the 
organs  by  which  new  individuals  are  formed,  as  the  reproduc- 
tive organs.  But  in  the  shark's  jaws,  and  others,  in  which  we 
see  row  after  row  of  teeth  succeeding  each  other?  the  row  be- 


306  NUTRITION. 

hind  is  not  formed  of  germs  derived  from  the  row  before :  the 
front  row  is  simply  repeated  in  the  second  one,  the  second  in 
the  third,  and  so  on.  So,  in  cuticle,  the  deepest  layer  of  epi- 
dermis-cells derives  no  germs  from  the  layer  above :  their  de- 
velopment is  not  like  a  reproduction  of  the  cells  that  have  gone 
on  towards  the  surface  before  them  :  it  is  only  a  repetition.  It 
is  not  improbable  that  much  of  the  difference  in  the  degree  of 
repair,  of  which  the  several  tissues  are  capable  after  injuries 
or  diseases,  may  be  connected  with  these  differences  in  their 
ordinary  mode  of  nutrition. 

In  order  that  the  process  of  nutrition  may  be  perfectly  ac- 
complished, certain  conditions  are  necessary.  Of  these,  the 
most  important  are :  1.  A  right  state  and  composition  of  the 
blood,  from  which  the  materials  for  nutrition  are  derived.  2. 
A  regular  and  not  far  distant  supply  of  such  blood.  3.  A  cer- 
tain influence  of  the  nervous  system.  4.  A  natural  state  of 
the  part  to  be  nourished. 

1.  This  right  condition  of  the  blood  does  not  necessarily  im- 
ply its  accordance  with  any  known  standard  of  composition, 
common  to  all  kinds  of  healthy  blood,  but  rather  the  existence 
of  a  certain  adaptation  between  the  blood  and  the  tissues,  and 
even  the  several  portions  of  each  tissue.  Such  an  adaptation, 
peculiar  to  each  individual,  is  determined  in  its  first  formation, 
and  is  maintained  in  the  concurrent  development  and  increase 
of  both  blood  and  tissues  ;  and  upon  its  maintenance  in  adult 
life  appears  to  depend  the  continuance  of  a  healthy  process  of 
nutrition,  or,  at  least,  the  preservation  of  that  exact  sameness 
of  the  whole  body  and  its  parts,  which  constitutes  the  perfec- 
tion of  nutrition.  Some  notice  of  the  maintenance  of  this 
sameness  in  the  blood  has  been  given  already  (p.  84),  in 
speaking  of  the  power  of  assimilation  which  the  blood  exer- 
cises, a  power  exactly  comparable  with  this  of  maintenance  by 
nutrition  in  the  tissues.  And  evidence  of  the  adaptation  be- 
tween the  blood  and  the  tissues,  and  of  the  exceeding  fineness 
of  the  adjustment  by  which  it  is  maintained,  is  afforded  by  the 
phenomena  of  diseases,  in  which,  after  the  introduction  of  cer- 
tain animal  poisons,  even  in  very  minute  quantities,  the  whole 
mass  of  the  blood  is  altered  in  composition,  and  the  solid  tis- 
sues are  perverted  in  their  nutrition.  It  is  necessary  to  refer 
only  to  such  diseases  as  syphilis,  small -pox,  and  other  erup- 
tive fevers,  in  illustration.  And  when  the  absolute  dependence 
of  all  the  tissues  on  the  blood  for  their  very  existence  is  re- 
membered, on  the  one  hand,  and,  on  the  other,  the  rapidity 
with  which  substances  introduced  into  the  blood  are  diffused 
into  all,  even  non-vascular  textures  (p.  297),  it  need  be  no 
source  of  wonder  that  any,  even  the  slightest  alteration,  from 


CONDITIONS   NECESSARY    FOR   NUTRITION.     307 

the  normal  constitution  of  the  blood,  should  be  immediately 
reflected,  so  to  speak,  as  a  change  in  the  nutrition  of  the 
solid  tissues  and  organs  which  it  is  destined  to  nourish. 

2.  The  necessity  of  an  adequate  supply  of  appropriate  blood 
in  or  near  the  part  to  be  nourished,  in  order  that  its  nutrition 
may  be  perfect,  is  shown  in  the  frequent  examples  of  atrophy 
of  parts  to  which  too  little  blood  is  sent,  of  mortification  or  ar- 
rested nutrition  when  the  supply  of  blood  is  entirely  cut  off, 
and  of  defective  nutrition  when  the  blood  is  stagnant  in  a  part. 
That  the  nutrition  of  a  part  may  be  perfect,  it  is  also  neces- 
sary that  the  blood  should  be  brought  sufficiently  near  to  it 
for  the  elements  of  the  tissue  to  imbibe,  through  the  walls  of 
the  bloodvessels,  the  nutritive  materials  which  they  require. 
The  bloodvessels  themselves  take  no  share  in  the  process  of 
nutrition,  except  as  carriers  of  the  nutritive  matter.  There- 
fore, provided  they  come  so  near  that  this  nutritive  matter 
may  pass  by  imbibition  into  the  part  to  be  nourished,  it  is 
comparatively  immaterial  whether  they  ramify  within  the 
substance  of  the  tissue,  or  are  distributed  only  on  its  surface 
or  border. 

The  bloodvessels  serve  alike  for  the  nutrition  of  the  vascular 
and  the  non-vascular  parts,  the  difference  between  which,  in 
regard  to  nutrition,  is  less  than  it  may  seem.  For  the  vascu- 
lar, the  nutritive  fluid  is  carried  in  streams  into  the  interior ; 
for  the  non-vascular,  it  flows  on  the  surface ;  but  in  both  alike, 
the  parts  themselves  imbibe  the  fluid  ;  and  although  the  pas- 
sage through  the  walls  of  the  bloodvessels  may  effect  some 
change  in  the  materials,  yet  all  the  process  of  formation  is, 
in  both  alike,  outside  the  vessels.  Thus,  in  muscular  tissue, 
the  fibrils  in  the  very  centre  of  the  fibre  nourish  themselves : 
yet  these  are  distant  from  all  bloodvessels,  and  can  only  by 
imbibition  receive  their  nutriment.  So,  in  bones,  the  spaces 
between  the  bloodvessels  are  wider  than  in  muscle ;  yet  the 
parts  in  the  meshes  nourish  themselves,  imbibing  materials 
from  the  nearest  source.  The  non-vascular  epidermis,  though 
no  vessels  pass  into  its  substance,  yet  imbibes  nutritive  matter 
from  the  vessels  of  the  immediately  subjacent  cutis,  and  main- 
tains itself,  and  grows.  The  instances  of  the  cornea  and  vitre- 
ous humor  are  stronger,  yet  similar ;  and  sometimes  even  the 
same  tissue  is  in  one  case  vascular,  in  the  other  not,  as  the 
osseous  tissue,  which,  when  it  is  in  masses  or  thick  layers,  has 
bloodvessels  running  into  it ;  but  when  it  is  in  thin  layers,  as 
in  the  lachrymal  and  turbinated  bones,  has  not.  .  These  bones 
subsist  on  the  blood  flowing  in  the  minute  vessels  of  the  mucous 
membrane,  from  which  the  epithelium  derives  nutriment  on 
one  side,  the  bone  on  the  other,  and  the  tissue  of  the  membrane 


308  NUTRITION. 

itself  on  every  side :  a  striking  instance  how,  from  the  same 
source,  many  tissues  maintain  themselves,  each  exercising  its 
peculiar  assimilative  and  self-formative  power. 

3.  The  third  condition  said  to  be  essential  to  a  healthy  nu- 
trition, is  a  certain  influence  of  the  nervous  system. 

It  has  been  held  that  the  nervous  system  cannot  be  essential 
to  a  healthy  course  of  nutrition,  because  in  plants  and  the 
early  embryo,  and  in  the  lowest  animals,  in  which  no  nervous 
system  is  developed,  nutrition  goes  on  without  it.  But  this  is 
no  proof  that  in  animals  which  have  a  nervous  system,  nutri- 
tion may  be  independent  of  it ;  rather  it  may  be  assumed,  that 
in  ascending  development,  as  one  system  after  another  is  added 
or  increased,  so  the  highest  (and,  highest  of  all,  the  nervous 
system)  will  always  be  inserted  and  blended  in  a  more  and 
more  intimate  relation  with  all  the  rest:  according  to  the 
general  law,  that  the  interdependence  of  parts  augments  with 
their  development. 

The  reasonableness  of  this  assumption  is  proved  by  many 
facts  showing  the  influence  of  the  nervous  system  on  nutrition, 
and  by  the  most  striking  of  these  facts  being  observed  in  the 
higher  animals,  and  especially  in  man.  The  influence  of  the 
mind  in  the  production,  aggravation,  and  cure  of  organic  dis- 
eases is  matter  of  daily  observation,  and  a  sufficient  proof  of 
influence  exercised  on  nutrition  through  the  nervous  system. 

Independently  of  mental  influence,  injuries  either  to  por- 
tions of  the  nervous  centres,  or  to  individual  nerves,  are  fre- 
quently followed  by  defective  nutrition  of  the  parts  supplied 
by  the  injured  nerves,  or  deriving  their  nervous  influence  from 
the  damaged  portions  of  the  nervous  centres.  Thus,  lesions  of 
the  spinal  cord  are  sometimes  followed  by  mortification  of  por- 
tions of  the  paralyzed  parts ;  and  this  may  take  place  very 
quickly,  as  in  a  case  by  Sir  B.  C.  Brodie,  in  which  the  ankle 
sloughed  within  twenty -four  hours  after  an  injury  of  the  spine. 
After  such  lesions  also,  the  repair  of  injuries  in  the  paralyzed 
parts  may  take  place  less  completely  than  in  others ;  so,  Mr. 
Travers  mentions  a  case  in  which  paraplegia  was  produced  by 
fracture  of  the  lumbar  vertebrae,  and,  in  the  same  accident,  the 
humerus  and  tibia  were  fractured.  The  former  in  due  time 
united  ;  the  latter  did  not.  The  same  fact  was  illustrated  by 
some  experiments  of  Dr.  Baly,  in  which  having,  in  salaman- 
ders, cut  off  the  end  of  the  tail,  and  then  thrust  a  thin  wire 
some  distance  up  the  spinal  canal,  so  as  to  destroy  the  cord,  he 
found  that  the  end  of  the  tail  was  reproduced  more  slowly  than 
in  other  salamanders  in  whom  the  spinal  cord  was  left  unin- 
jured above  the  point  at  which  the  tail  was  amputated.  Illus- 
trations of  the  same  kind  are  furnished  by  the  several  cases  in 


INFLUENCE    OF    NERVOUS    SYSTEM.          309 

which  division  or  destruction  of  the  trunk  of  the  trigeminal 
nerve  has  been  followed  by  incomplete  and  morbid  nutrition 
of  the  corresponding  side  of  the  face;  ulceration  of  the  cornea 
being  often  directly  or  indirectly  one  of  the  consequences  of 
such  imperfect  nutrition.  Part  of  the  wasting  and  slow  de- 
generation of  tissue  in  paralyzed  limbs  is  probably  referable 
also  to  the  withdrawal  of  nervous  influence  from  them;  though, 
perhaps,  more  is  due  to  the  want  of  use  of  the  tissues. 

Undue  irritation  of  the  trunks  of  nerves,  as  well  as  their 
division  or  destruction,  is  sometimes  followed  by  defective 
or  morbid  nutrition.  To  this  may  be  referred  the  cases  in 
which  ulceration  of  the  parts  supplied  by  the  irritated  nerves 
occurs  frequently,  and  continues  so  long  as  the  irritation  lasts. 
Further  evidence  of  the  influence  of  the  nervous  system  upon 
nutrition  is  furnished  by  those  cases  in  which,  from  mental  an- 
guish, or  in  severe  neuralgic  headaches,  the  hair  becomes  gray 
very  quickly,  or  even  in  a  few  hours. 

So  many  and  various  facts  leave  little  doubt  that  the  ner- 
vous system  exercises  an  influence  over  nutrition  as  over  other 
organic  processes ;  and  they  cannot  be  explained  by  supposing 
that  the  changes  in  the  nutritive  processes  are  only  due  to  the 
variations  in  the  size  of  the  bloodvessels  supplying  the  affected 
parts. 

The  question  remains,  through  what  class  of  nerves  is  the 
influence  exerted?  When  defective  nutrition  occurs  in  parts 
rendered  inactive  by  injury  of  the  motor  nerve  alone,  as  in  the 
muscles  and  other  tissues  of  a  paralyzed  face  or  limb,  it  may 
appear  as  if  the  atrophy  were  the  direct  consequence  of  the 
loss  of  power  in  the  motor  nerves  ;  but  it  is  more  probable  that 
the  atrophy  is  the  consequence  of  the  want  of  exercise  of  the 
parts ;  for  if  the  muscles  be  exercised  by  artificial  irritation  of 
their  nerves  their  nutrition  will  be  less  defective  (J.  Reid). 
The  defect  of  the  nutritive  process  which  ensues  in  the  face 
and  other  parts,  moreover,  in  consequence  of  destruction  of  the 
trigeminal  nerve,  cannot  be  referred  to  loss  of  influence  of  any 
motor  nerves;  for  the  motor  nerves  of  the  face  and  eye,  as  well 
as  the  olfactory  and  optic,  have  no  share  in  the  defective  nu- 
trition which  follows  injury  of  the  trigeminal  nerve ;  and  one 
or  all  of  them  may  be  destroyed  without  any  direct  disturbance 
of  the  nutrition  of  the  parts  they  severally  supply. 

It  must  be  concluded,  therefore,  that  the  influence  which  is 
exercised  by  nerves  over  the  nutrition  of  parts  to  which  they 
are  distributed  is  to  be  referred  either  to  those  among  their 
branches  which  conduct  impressions  to  the  brain  and  spinal 
cord,  namely,  the  nerves  of  common  sensation,  or,  as  it  is  by 
some  supposed,  by  nerve-fibres  which  preside  specially  over 


310  NUTRITION. 

the  nutrition  of  the  tissues  and  organs  to  which  they  are  sup- 
plied. Such  special  nerves  are  called  trophic  nerves  (see  chap- 
ter on  the  Nervous  System). 

It  is  not  at  present  possible  to  say  whether  the  influence  on 
nutrition  is  exercised  through  the  cerebro-spinal  or  through  the 
sympathetic  nerves,  which,  in  the  parts  on  which  the  observa- 
tion has  been  made,  are  generally  combined  in  the  same  sheath. 
The  truth  perhaps  is,  that  it  may  be  exerted  through  either  or 
both  of  these  nerves.  The  defect  of  nutrition  which  ensues 
after  lesion  of  the  spinal  cord  alone,  the  sympathetic  nerves 
being  uninjured,  and  the  general  atrophy  which  sometimes 
occurs  in  consequence  of  diseases  of  the  brain,  seem  to  prove 
the  influence  of  the  cerebro-spinal  system :  while  the  observa- 
tion of  Magendie  and  Mayer,  that  inflammation  of  the  eye  is 
a  constant  result  of  ligature  of  the  sympathetic  nerve  in  the 
neck,  and  many  other  observations  of  a  similar  kind,  exhibit 
very  well  the  influence  of  the  latter  nerve  in  nutrition. 

4.  The  fourth  condition  necessary  to  healthy  nutrition  is  a 
healthy  state  of  the  part  to  be  nourished.  This  seems  proved 
by  the  very  nature  of  the  process,  which  consists  in  the  forma- 
tion of  new  parts  like  those  already  existing ;  for,  unless  the 
latter  are  healthy,  the  former  cannot  be  so.  Whatever  be  the 
condition  of  a  part,  it  is  apt  to  be  perpetuated  by  assimilating 
exactly  to  itself,  and  endowing  with  all  its  peculiarities,  the 
new  particles  which  it  forms  to  replace  those  that  degenerate. 
So  long  as  a  part  is  healthy,  and  the  other  conditions  of  healthy 
nutrition  exist,  it  maintains  its  healthy  condition.  But,  ac- 
cording to  the  same  law,  if  the  structure  of  a  part  be  diseased 
or  in  any  way  altered  from  its  natural  condition,  the  alteration 
is  maintained ;  the  altered,  like  the  healthy  structure,  is  per- 
petuated. 

The  same  exactness  of  the  assimilation  of  the  new  parts  to 
the  old,  which  is  seen  in  the  nutrition  of  the  healthy  tissues, 
may  be  observed  also  in  those  that  are  formed  in  disease.  By 
it,  the  exact  form  and  relative  size  of  a  cicatrix  are  preserved 
from  year  to  year ;  by  it,  the  thickening  and  induration  to 
which  inflammation  gives  rise  are  kept  up,  and  the  various 
morbid  states  of  the  blood  in  struma,  syphilis,  and  other  chronic 
diseases  are  maintained,  notwithstanding  all  diversities  of  diet. 
By  this  precision  of  the  assimilating  process,  may  be  explained 
the  law  that  certain  diseases  occur  only  once  in  the  same  per- 
son, and  that  certain  others  are  apt  to  recur  frequently ;  because 
in  both  cases  alike,  the  alteration  produced  by  the  first  attack 
of  the  disease  is  maintained  by  the  exact  likeness  which  the 
new  parts  bear  to  the  old  ones. 

The  period,  however,  during  which  an  alteration  of  structure 


GROWTH.  311 

may  be  exactly  maintained  by  nutrition,  is  not  unlimited;  for 
in  nearly  all  altered  parts  there  appears  to  exist  a  tendency  to 
recover  the  perfect  state ;  and,  in  many  cases,  this  state  is,  in 
time,  attained.  To  this  we  may  attribute  the  possibility  of  re- 
vaccination  after  the  lapse  of  some  years ;  the  occasional  recur- 
rence of  small-pox,  scarlet-fever,  and  the  like  diseases,  in  the 
same  person ;  the  wearing  out  of  scars,  and  the  complete  restor- 
ation of  tissues  that  have  been  altered  by  injury  or  disease. 

Such  are  some  of  the  more  important  conditions  which  ap- 
pear to  be  essential  to  healthy  nutrition.  Absence  or  defect  of 
any  one  of  them  is  liable  to  be  followed  by  disarrangement  of 
the  process ;  and  the  various  diseases  resulting  from  defective 
nutrition  appear  to  be  due  to  the  failure  of  these  conditions, 
more  often  than  to  imperfection  of  the  process  itself. 

GROWTH. 

Growth,  as  has  been  already  observed,  consists  in  the  increase 
of  a  part  in  bulk  and  weight  by  the  addition  to  its  substance 
of  particles  similar  to  its  own,  but  more  than  sufficient  to  re- 
place those  which  it  loses  by  the  waste  or  natural  decay  of  its 
tissue.  The  structure  and  composition  of  the  part  remain  the 
same ;  but  the  increase  of  healthy  tissue  which  it  receives  is 
attended  with  the  capability  of  discharging  a  larger  amount  of 
its  ordinary  function. 

While  development  is  in  progress,  growth  frequently  pro- 
ceeds with  it  in  the  same  part,  as  in  the  formation  of  the 
various  organs  and  tissues  of  the  embryo,  in  which  parts,  while 
they  grow  larger,  are  also  gradually  more  developed  until  they 
attain  their  perfect  state.  But,  commonly,  growth  continues 
after  development  is  completed,  and  in  some  parts,  continues 
even  after  the  full  stature  of  the  body  is  attained,  and  after 
nearly  every  portion  of  it  has  gained  its  perfect  state  in  both 
size  and  composition. 

In  certain  conditions,  this  continuance  or  a  renewal  of 
growth  may  be  observed  in  nearly  every  part  of  the  body. 
When  parts  have  attained  the  full  size  which  in  the  ordinary 
process  of  growth  they  reach,  and  are  then  kept  in  a  moderate 
exercise  of  their  functions,  they  commonly  (as  already  stated) 
retain  almost  exactly  the  same  dimensions  through  the  adult 
period  of  life.  But  when,  from  any  cause,  a  part  already  full- 
grown  in  proportion  to  the  rest  of  the  body,  is  called  upon  to 
discharge  an  unusual  amount  of  its  ordinary  function,  the 
demand  is  met  by  a  corresponding  increase  or  growth  of  the 
part.  Illustrations  of  this  are  afforded  by  the  increased  thick- 
ening of  cuticle  at  parts  where  it  is  subjected  to  an  unusual 


312  NUTRITION. 

degree  of  occasional  pressure  or  friction,  as  in  the  palms  of 
the  hands  of  persons  employed  in  rough  manual  labor ;  by 
the  enlargement  and  increased  hardness  of  muscles  that  are 
largely  exercised  ;  and  by  many  other  facts  of  a  like  kind. 
The  increased  power  of  nutrition  put  forth  in  such  growth  is 
greater  than  might  be  supposed ;  for  the  immediate  effect  of 
increased  exercise  of  a  part  must  be  a  greater  using  of  its 
tissue,  and  might  be  expected  to  entail  a  permanent  thinning 
or  diminution  of  the  substance  of  the  part.  But  the  energy 
with  which  fresh  particles  are  formed  is  sufficient  not  only  to 
replace  completely  those  that  are  worn  away,  but  to  cause  an 
increase  in  the  substance  of  the  part — the  amount  of  this  in- 
crease being  proportioned  to  the  more  than  usual  degree  in 
which  its  functions  are  exercised. 

The  growth  of  a  part  from  undue  exercise  of  its  functions 
is  always,  in  itself,  a  healthy  process ;  and  the  increased  size 
which  results  from  it  must  be  distinguished  from  the  various 
kind  of  enlargement  to  which  the  same  part  may  be  subject 
from  disease.  In  the  former  case,  the  enlargement  is  due  to 
an  increased  quantity  of  healthy  tissue,  providing  more  than 
the  previous  power  to  meet  a  particular  emergency ;  the  other 
may  be  the  result  of  a  deposit  of  morbid  material  within  the 
natural  structure  of  the  part,  diminishing,  instead  of  augment- 
ing, its  fitness  for  its  office.  Such  a  healthy  process  of  growth 
in  a  part,  attended  with  increased  power  and  activity  of  its 
functions,  may,  however,  occur  as  the  consequence  of  disease 
in  some  other  part;  in  which  case  it  is  commonly  called  Hy- 
pertrophy, i.  e.,  excess  of  nutrition.  The  most  familiar  ex- 
amples of  this  are  in  the  increased  thickness  and  robustness 
of  the  muscular  walls  of  the  cavities  of  the  heart  in  cases  of 
continued  obstruction  to  the  circulation  ;  and  in  the  increased 
development  of  the  muscular  coat  of  the  urinary  bladder 
when,  from  any  cause,  the  free  discharge  of  urine  from  it  is 
interfered  with.  In  both  these  cases,  though  the  origin  of  the 
growth  is  the  consequence  of  disease,  yet  the  growth  itself  is 
natural,  and  its  end  is  the  benefit  of  the  economy ;  it  is  only 
common  growth  renewed  or  exercised  in  a  part  which  had 
attained  its  size  in  due  proportion  to  the  rest  of  the  body. 

It  may  be  further  mentioned,  in  relation  to  the  physiology 
of  this  subject,  that  when  the  increase  of  function,  which  is 
requisite  in  the  cases  from  which  hypertrophy  results,  cannot 
be  efficiently  discharged  by  mere  increase  of  the  ordinary 
tissue  of  the  part,  the  development  of  a  new  and  higher  kind 
of  tissue  is  frequently  combined  with  this  growth.  An  exam- 
ple of  this  is  furnished  by  the  uterus,  in  the  walls  of  which, 
whei|  it  becomes  enlarged  by  pregnancy,  or  by  the  growth  of 


SECRETION.  313 

fibrous  tumors,  organic  muscular  fibres,  found  in  a  very  ill- 
developed  condition  in  its  quiescent  state,  are  then  enormously 
developed,  and  provide  for  the  expulsion  of  the  foetus  or-  the 
foreign  body.  Other  examples  of  the  same  kind  are  furnished 
by  cases  in  which,  from  obstruction  to  the  discharge  of  their 
contents  and  a  consequently  increased  necessity  for  propulsive 
power,  the  coats  of  reservoirs  and  of  ducts  become  the  seat 
of  development  of  organic  muscular  fibres,  which  could  be 
said  only  just  to  exist  in  them  before,  or  were  present  in  a 
very  imperfectly  developed  condition. 

Respecting  the  mode  and  conditions  of  the  process  of  growth, 
it  need  only  be  said,  that  its  mode  seems  to  differ  only  in  de- 
gree from  that  of  common  maintenance  of  a  part ;  more  par- 
ticles are  removed  from,  and  many  more  added  to  a  growing 
tissue,  than  to  one  which  only  maintains  itself.  But  so  far 
as  can  be  ascertained,  the  mode  of  removal,  the  disposition  of 
the  removed  parts,  and  the  insertion  of  the  new  particles,  are 
as  in  simple  maintenance. 

The  conditions  also  of  growth  are  the  same  as  those  of  com- 
mon nutrition,  and  are  equally  or  more  necessary  to  its  occur- 
rence. When  they  are  very  favorable  or  in  excess,  growth 
may  occur  in  the  place  of  common  nutrition.  Thus  hair  may 
grow  profusely  in  the  neighborhood  of  old  ulcers,  in  consequence, 
apparently,  of  the  excessive  supply  of  blood  to  the  hair-bulbs 
and  pulps ;  bones  may  increase  in  length  when  disease  brings 
much  blood  to  them ;  and  cocks'  spurs  transplanted  from  their 
legs  into  their  combs  grow  to  an  unnatural  length ;  the  conditions 
common  to  all  these  cases  being  both  an  increased  supply  of 
blood,  and  the  capability,  on  the  part  of  the  growing  tissue,  of 
availing  itself  of  the  opportunity  of  increased  absorption  and 
nutrition  thus  afforded  to  it.  In  the  absence  of  the  last-named 
condition,  increased  supply  of  blood  will  not  lead  to  increased 
nutrition. 


CHAPTER  XII. 

SECRETION. 


SECRETION  is  the  process  by  which  materials  are  separated 
from  the  blood,  and  from  the  organs  in  which  they  are  formed, 
for  the  purpose  either  of  serving  some  ulterior  office  in  the 
economy,  or  being  discharged  from  the  body  as  excrement.  In 
the  former  case,  both  the  separated  materials  and  the  processes 


314  SECKETION. 

for  their  separation  are  termed  secretions;  in  the  latter,  they 
are  named  excretions. 

Most  of  the  secretions  consist  of  substances  which,  probably, 
do  not  pre-exist  in  the  same  form  in  the  blood,  but  require 
special  organs  and  a  process  of  elaboration  for  their  formation, 
e.  g.,  the  liver  for  the  formation  of  bile,  the  mammary  gland 
for  the  formation  of  milk.  The  excretions,  on  the  other  hand, 
commonly  or  chiefly  consist  of  substances  which,  as  urea,  car- 
bonic acid,  and  probably  uric  acid,  exist  ready-formed  in  the 
blood,  and  are  merely  abstracted  therefrom.  If  from  any 
cause,  such  as  extensive  disease  or  extirpation  of  an  excretory 
organ,  the  separation  of  an  excretion  is  prevented,  and  an  ac- 
cumulation of  it  in  the  blood  ensues,  it  frequently  escapes 
through  other  organs,  and  may  be  detected  in  various  fluids  of 
the  body.  But  this  is  never  the  case  with  secretions ;  at  least 
with  those  that  are  most  elaborated ;  for  after  the  removal  of  the 
special  organs  by  which  any  of  them  is  elaborated,  it  is  no  longer 
formed.  Cases  sometimes  occur  in  which  the  secretion  con- 
tinues to  be  formed  by  the  natural  organ,  but  not  being  able  to 
escape  towards  the  exterior,  on  account  of  some  obstruction,  is 
reabsorbed  into  the  blood,  and  afterwards  discharged  from  it 
by  exudation  in  other  ways ;  but  these  are  not  instances  of  true 
vicarious  secretion,  and  must  not  be  thus  regarded. 

These  circumstances,  and  their  final  destination,  are,  how- 
ever, the  only  particulars  in  which  secretions  and  excretions 
can  be  distinguished  ;  for,  in  general,  the  structure  of  the  parts 
engaged  in  eliminating  excretions,  e.  g.,  the  kidneys,  is  as  com- 
plex as  that  of  the  parts  concerned  in  the  formation  of  secre- 
tions. And  since  the  diiferences  of  the  two  processes  of  sepa- 
ration, corresponding  with  those  in  the  several  purposes  and 
destinations  of  the  fluids,  are  not  yet  ascertained,  it  will  be 
sufficient  to  speak  in  general  terms  of  the  process  of  separation 
or  secretion. 

Every  secreting  apparatus  possesses,  as  essential  parts  of  its 
structure,  a  simple  and  apparently  textureless  membrane, 
named  the  primary  or  basement-membrane ;  certain  cells ;  and 
bloodvessels.  These  three  structural  elements  are  arranged 
together  in  various  ways ;  but  all  the  varieties  may  be  classed 
under  one  or  other  of  two  principal  divisions,  namely,  mem- 
branes and  glands. 

SECRETING    MEMBRANES. 

The  principal  secreting  membranes  are  the  serous  and  syno- 
vial  membranes,  the  mucous  membranes,  and  the  skin.1 

1  The  skin  will  be  described  in  a  subsequent  chapter. 


SEROUS     MEMBRANES.  315 

The  serous  membranes  are  formed  of  fibro-cellular  tissue, 
interwoven  so  as  to  constitute  a  membrane,  the  free  surface  of 
which  is  covered  with  a  single  layer  of  flattened  cells,  forming, 
in  most  instances,  a  simple  tessellated  epithelium.  Between  the 
epithelium  and  the  subjacent  layer  of  fibro-cellular  tissue,  is 
situated  the  primary  or  basement-membrane  (Bowman). 

FIG. 104. 


Plan  of  a  secreting  membrane :  a,  membrana  propria,  or  basement-membrane ;  6, 
epithelium  composed  of  secreting  nucleated  cells ;  c,  layer  of  capillary  bloodvessels 
(after  Sharpey). 

In  relation  to  the  process  of  secretion,  the  layer  of  fibro- 
cellular  tissue  serves  as  a  groundwork  for  the  ramification  of 
bloodvessels,  lymphatics,  and  nerves.  But  in  its  usual  form 
it  is  absent  in  some  instances,  as  in  the  arachnoid  covering  the 
dura  mater,  and  in  the  interior  of  the  ventricles  of  the  brain. 
The  primary  membrane  and  epithelium  are  probably  always 
present,  and  are  concerned  in  the  formation  of  the  fluid  by 
which  the  free  surface  of  the  membrane  is  moistened. 

The  serous  membranes  are  of  two  principal  kinds:  1st. 
Those  which  line  visceral  cavities, — the  arachnoid,  pericar- 
dium, pleurae,  peritoneum,  and  tunicse  vaginales.  2d.  The 
synovial  membranes  lining  the  joints,  and  the  sheaths  of  ten- 
dons and  ligaments,  with  which,  also,  are  usually  included  the 
synovial  bursse,  or  bursce  mucosce,  whether  these  be  subcuta- 
neous, or  situated  beneath  tendons  that  glide  over  bones. 

The  serous  membranes  form  closed  sacs,  and  exist  wherever 
the  free  surfaces  of  viscera  come  into  contact  with  each  other, 
or  lie  in  cavities  unattached  to  surrounding  parts.  The  viscera, 
which  are  invested  by  a  serous  membrane,  are,  as  it  were, 
pressed  into  the  shut  sac  which  it  forms,  carrying  before  them 
a  portion  of  the  membrane,  which  serves  as  their  investment. 
To  the  law  that  serous  membranes  form  shut  sacs,  there  is,  in 
the  human  subject,  one  exception,  viz. :  the  opening  of  the 
Fallopian  tubes  into  the  abdominal  cavity, — an  arrangement 
which  exists  in  man  and  all  Vertebrata,  with  the  exception  of 
a  few  fishes. 

The  principal  purpose  of  the  serous  and  synovial  membranes 
is  to  furnish  a  smooth,  moist  surface,  to  facilitate  the  move- 
ments of  the  invested  organ,  and  to  prevent  the  injurious 
effects  of  friction.  This  purpose  is  especially  manifested  in 


316  SECRETION. 

joints,  in  which  free  and  extensive  movements  take  place  ;  and 
in  the  stomach  and  intestines,  which,  from  the  varying  quan- 
tity and  movements  of  their  contents,  are  in  almost  constant 
motion  upon  one  another  and  the  walls  of  the  abdomen. 

The  fluid  secreted  from  the  free  surface  of  the  serous  mem- 
branes is,  in  health,  rarely  more  than  sufficient  to  insure  the 
maintenance  of  their  moisture.  The  opposed  surfaces  of  each 
serous  sac,  are  at  every  point  in  contact  with  each  other,  and 
leave  no  space  in  which  fluid  can  collect.  After  death,  a  larger 
quantity  of  fluid  is  usually  found  in  each  serous  sac ;  but  this, 
if  not  the  product  of  manifest  disease,  is  probably  such  as  has 
transuded  after  death,  or  in  the  last  hours  of  life.  An  excess 
of  such  fluid  in  any  of  the  serous  sacs  constitutes  dropsy  of  the 
sac. 

The  fluid  naturally  secreted  by  the  serous  membranes  appears 
to  be  identical,  in  general  and  chemical  characters,  with  the 
serum  of  the  blood,  or  with  very  dilute  liquor  sanguinis.  It 
is  of  a  pale  yellow  or  straw-color,  slightly  viscid,  alkaline,  and, 
because  of  the  presence  of  albumen,  coagulable  by  heat.  The 
presence  of  a  minute  quantity  of  fibrin,  at  least  in  the  dropsical 
fluids  effused  into  the  serous  cavities,  is  shown  by  their  partial 
coagulation  into  a  jelly-like  mass,  on  the  addition  of  certain 
animal  substances,  or  on  mixture  with  certain  fluids,  especially 
such  as  contain  cells  (p.  70  et  seq.}.  This  similarity  of  the  serous 
fluid  to  the  liquid  part  of  blood,  and  to  the  fluid  with  which 
most  animal  tissues  are  moistened,  renders  it  probable  that  it 
is,  in  great  measure,  separated  by  simple  transudation  through 
the  walls  of  the  bloodvessels.  The  probability  is  increased  by 
the  fact  that,  in  jaundice,  the  fluid  in  the  serous  sacs  is,  equally 
with  the  serum  of  the  blood,  colored  with  the  bile.  But  there 
is  reason  for  supposing  that  the  fluid  of  the  cerebral  ventricles 
and  of  the  arachnoid  sac  are  exceptions  to  this  rule ;  for  they 
differ  from  the  fluids  of  the  other  serous  sacs  not  only  in  being 
pellucid,  colorless,  and  of  much  less  specific  gravity,  but  in 
that  they  seldom  receive  the  tinge  of  bile  in  the  blood,  and  are 
not  colored  by  madder,  or  other  similar  substances  introduced 
abundantly  into  the  blood. 

It  is  also  probable  that  the  formation  of  synovial  fluid  is  a 
process  of  more  genuine  and  elaborate  secretion,  by  means  of 
the  epithelial  cells  on  the  surface  of  the  membrane,  and  espe- 
cially of  those  which  are  accumulated  on  the  edges  and  pro- 
cesses of  the  synovial  fringes ;  for,  in  its  peculiar  density,  vis- 
cidity, and  abundance  of  albumen,  synovia  differs  alike  from 
the  serum  of  blood  and  from  the  fluid  of  any  of  the  serous 
cavities. 

The  mucous  membranes  line  all  those  passages  by  which  in- 


MUCOUS    MEMBRANES.  317 

ternal  parts  communicate  with  the  exterior,  and  by  which  either 
matters  are  eliminated  from  the  body  or  foreign  substances 
taken  into  it.  They  are  soft  and  velvety,  and  extremely  vas- 
cular. Their  general  structure  resembles  that  of  serous  mem- 
branes. It  consists  of  epithelium,  basement-membrane,  and 
fibro-cellular  or  areolar  tissue  containing  bloodvessels,  lym- 
phatics, and  nerves.  The  structure  of  mucous  membranes  is 
less  uniform,  especially  as  regards  their  epithelium,  than  that 
of  serous  membranes ;  but  the  varieties  of  structure  in  different 
parts  are  described  in  connection  with  the  organs  in  which 
mucous  membranes  are  present,  and  need  not  be  here  noticed 
in  detail.  The  external  surfaces  of  mucous  membranes  are 
attached  to  various  other  tissues ;  in  the  tongue,  for  example, 
to  muscle ;  on  cartilaginous  parts,  to  perichondrium  ;  in  the 
cells  of  the  ethmoid  bone,  in  the  frontal  and  sphenoid  sinuses, 
as  well  as  in  the  tympanum,  to  periosteum ;  in  the  intestinal 
canal,  it  is  connected  with  a  firm  submucous  membrane,  which 
on  its  exterior  gives  attachment  to  the  fibres  of  the  muscular 
coat. 

The  mucous  membranes  are  described  as  lining  certain  prin- 
cipal tracts.  1.  The  digestive  trad  commences  in  the  cavity  of 
the  mouth,  from  which  prolongations  pass  into  the  ducts  of  the 
salivary  glands.  From  the  mouth  it  passes  through  the  fauces, 
pharynx,  and  oesophagus,  to  the  stomach,  and  is  thence  con- 
tinued along  the  whole  tract  of  the  intestinal  canal  to  the  ter- 
mination of  the  rectum,  being  in  its  course  arranged  in  the 
various  folds  and  depressions  already  described,  and  prolonged 
into  the  ducts  of  the  pancreas  and  liver  and  into  the  gall-blad- 
der. 2.  The  respiratory  tract  includes  the  mucous  membrane 
lining  the  cavity  of  the  nose,  and  the  various  sinuses  commu- 
nicating with  it,  the  lachrymal  canal  and  sac,  the  conjunctiva 
of  the  eye  and  eyelids,  and  the  prolongation  which  passes  along 
the  Eustachian  tubes  and  lines  the  tympanum  and  the  inner 
surface  of  the  membrana  tympani.  Crossing  the  pharynx,  and 
lining  that  part  of  it  which  is  above  the  soft  palate,  the  respi- 
ratory tract  leads  into  the  glottis,  whence  it  is  continued,  through 
the  larynx  and  trachea,  to  the  bronchi  and  their  divisions, 
which  it  lines  as  far  as  the  branches  of  about  -£$  of  an  inch  in 
diameter,  and  continuous  with  it  is  a  layer  of  delicate  epithelial 
membrane  which  extends  into  the  pulmonary  cells.  3.  The 
genito-urinary  tract,  which  lines  the  whole  of  the  urinary  pas- 
sages, from  their  external  orifice  to  the  termination  of  the 
tubuli  uriniferi  of  the  kidneys,  extends  into  and  through  the 
organs  of  generation  in  both  sexes,  into  the  ducts  of  the  glands 
connected  with  them ;  and  in  the  female  becomes  continuous 

27 


318  SECRETION. 

with  the  serous  membrane  of  the  abdomen  at  the  fimbrise  of 
the  Fallopian  tubes. 

Along  each  of  the  above  tracts,  and  in  different  portions  of 
each  of  them,  the  mucous  membrane  pres'ents  certain  struc- 
tural peculiarities  adapted  to  the  functions  which  each  part 
has  to  discharge;  yet  in  some  essential  characters  mucous 
membrane  is  the  same,  from  whatever  part  it  is  obtained.  In 
all  the  principal  and  larger  parts  of  the  several  tracts,  it  pre- 
sents, as  just  remarked,  an  external  layer  of  epithelium, 
situated  upon  basement-membrane,  and  beneath  this,  a  stratum 
of  vascular  tissue  of  variable  thickness,  which  in  different  cases 
presents  either  outgrowths  in  the  form  of  papillae  and  villi,  or 
depressions  or  involutions  in  the  form  of  glands.  But  in  the 
prolongations  of  the  tracts,  where  they  pass  into  gland-ducts, 
these  constituents  are  reduced  in  the  finest  branches  of  the 
ducts  to  the  epithelium,  the  primary  or  basement-membrane, 
and  the  capillary  bloodvessels  spread  over  the  outer  surface 
of  the  latter  in  a  single  layer. 

The  primary  or  basement-membrane  is  a  thin  transparent 
layer,  simple,  homogeneous,  and  with  no  discernible  structure, 
which  on  the  larger  mucous  membranes  that  have  a  layer  of 
vascular  fibro-cellular  tissue,  may  appear  to  be  only  the 
blastema  or  formative  substance,  out  of  which  successive 
layers  of  epithelium-cells  are  formed.  But  in  the  minuter  di- 
visions of  the  mucous  membranes,  and  in  the  ducts  of  glands, 
it  is  the  layer  continuous  and  correspondent  with  this  basement- 
membrane  that  forms  the  proper  walls  of  the  tubes.  The  cells 
also  which,  lining  the  larger  and  coarser  mucous  membranes, 
constitute  their  epithelium,  are  continuous  with  and  often 
similar  to  those  which,  lining  the  gland-ducts,  are  called 
gland-cells,  rather  than  epithelium.  Indeed,  no  certain  dis- 
tinction can  be  drawn  between  the  epithelium-cells  of  mucous 
membranes  and  gland-cells.  In  reference  to  their  position,  as 
covering  surfaces,  they  might  all  be  called  epithelium-cells, 
whether  they  lie  on  open  mucous  membranes,  or  in  gland- 
ducts  ;  and  in  reference  to  the  process  of  secretion,  they  might 
all  be  called  gland-cells,  or  at  least  secreting-cells,  since  they 
probably  all  fulfil  a  secretory  office  by  separating  certain 
definite  materials  from  the  blood  and  from  the  part  on  which 
they  are  seated.  It  is  only  an  artificial  distinction  which 
makes  them  epithelial  cells  in  one  place,  and  gland-cells  in 
another. 

It  thus  appears,  that  the  tissues  essential  to  the  production 
of  a  secretion  are,  in  their  simplest  form,  a  simple  membrane, 
having  on  one  surface  bloodvessels,  and  on  the  other  a  layer  of 
cells,  which  may  be  called  either  epithelium-cells  or  gland- 


SECRETING    GLANDS.  319 

cells.  Glands  are  provided  also  with  lymphatic  vessels  and 
nerves.  The  distribution  of  the  former  is  not  peculiar,  and 
need  not  be  here  considered.  Nerve-fibres  are  distributed 
both  to  the  bloodvessels  of  the  gland  and  to  its  ducts ;  and, 
in  some  glands,  it  is  said,  to  the  secreting  cells  also. 

The  structure  of  the  elementary  portions  of  a  secreting  ap- 
paratus, namely,  epithelium,  simple  membrane,  and  blood- 
vessels, having  been  already  described  in  this  and  previous 
chapters,  we  may  proceed  to  consider  the  manner  in  which 
they  are  arranged  to  form  the  varieties  of  secreting  glands. 

SECRETING   GLANDS. 

The  secreting  glands  are  the  organs  to  which  the  office  of 
secreting  is  more  especially  ascribed :  for  they  appear  to  be 
occupied  with  it  alone.  They  present,  amid  manifold  diversi- 
ties of  form  and  composition,  a  general  plan  of  structure,  by 
which  they  are  distinguished  from  all  other  textures  of  the 
body;  especially,  all  contain,  and  appear  constructed  with 
particular  regard  to,  the  arrangement  of  the  cells,  which  as 
already  expressed,  both  line  their  tubes  or  cavities  as  an  epi- 
thelium, and  elaborate,  as  secreting  cells,  the  substances  to  be 
discharged  from  them. 

For  convenience  of  description,  they  may  be  divided  into 
three  principal  groups,  the  characters  of  each  of  which  are  de- 
termined by  the  different  modes  in  which  the  sacculi  or  tubes 
containing  the  secreting  cells  are  grouped  : 

1.  The  simple  tubule  or  tubular  gland  (A,  Fig.  105),  exam- 
ples of  which  are  furnished  by  the  several  tubular  follicles  in 
mucous  membranes :  especially  by  the  follicles  of  Lieberkiihn 
in  the  mucous  membrane  of  the  intestinal  canal  (p.  241),  and 
the  tubular  or  gastric  glands  of  the  stomach  (p.  217).     These 
appear  to  be  simple  tubular  depressions  of  the  mucous  mem- 
brane on  which  they  open,  each  consisting  of  an  elongated 
gland- vesicle,  the  wall  of  which  is  formed  of  primary  mem- 
brane, and  is  lined  with  secreting  cells  arranged  as  an  epithe- 
lium.    To  the  same  class  may  be  referred  the  elongated  and 
tortuous  sudoriparous  glands  of  the  skin  (p.  338),  and  the 
Meibomian  follicles  beneath  the  palpebral  conjunctiva ;  though 
the  latter  are  made  more  complex  by  the  presence  of  small 
pouches  along  their  sides  (B,  Fig.  105),  and  form  a  connecting 
link  between  the  members  of  this  division  and  the  next,  as  the 
former  by  their  length  and  tortuosity  do  between  the  first  di- 
vision and  the  third  (D,  Fig.  105). 

2.  The  aggregated  glands,  including  those  that  used  to  be 
called  conglomerate,  in  which  a  number  of  vesicles  or  acini  are 


320 


SECKETION. 


arranged  in  groups  or  lobules  (c,  Fig.  105).  Such  are  all 
those  commonly  called  mucous  glands,  as  those  of  the  tra- 
chea, vagina,  and  the  minute  salivary  glands.  Such,  also,  are 


Plans  of  extension  of  secreting  membrane  by  inversion  or  recession  in  form  of 
cavities.  A,  simple  glands,  viz.,  g,  straight  tube  ;  h,  sac  ;  i,  coiled  tube.  B,  multi- 
Jocular  crypts  ;  k,  of  tubular  form  ;  I,  saccular.  C,  racemose,  or  saccular  compound 
gland ;  TO,  entire  gland,  showing  branched  duct  and  lobular  structure ;  »,  a  lobule, 
detached  with  o,  branch  of  duct  proceeding  from  it.  D,  compound  tubular  gland 
(after  Sharpey). 

the    lachrymal,   the   large  salivary   and   mammary   glands, 
Brunn's,  Cowper's,  and  fiuverney's  glands,  the  pancreas  and 


PROCESS    OF    SECRETION.  321 

prostate.  These  various  organs  differ  from  each  other  only 
in  secondary  points  of  structure  ;  such  as,  chiefly,  the  arrange- 
ment of  their  excretory  ducts,  the  grouping  of  the  acini  and 
lobules,  their  connection  by  fibro-cellular  tissue,  and  supply  of 
bloodvessels.  The  acini  commonly  appear  to  be  formed  by  a 
kind  of  fusion  of  the  walls  of  several  vesicles,  which  thus  com- 
bine to  form  one  cavity  lined  or  filled  with  secreting  cells 
which  also  occupy  recesses  from  the  main  cavity.  The  small- 
est branches  of  the  gland-ducts  sometimes  open  into  the  cen- 
tres of  these  cavities ;  sometimes  the  acini  are  clustered  round 
the  extremities,  or  by  the  sides  of  the  ducts :  but,  whatever 
secondary  arrangement  there  may  be,  all  have  the  same  essen- 
tial character  of  rounded  groups  of  vesicles  containing  gland- 
cells,  and  opening,  either  occasionally  or  permanently,  by  a 
common  central  cavity  into  minute  ducts,  which  ducts  in  the 
large  glands  converge  and  unite  to  form  larger  and  larger 
branches,  and  at  length,  by  one  common  trunk,  open  on  a  free 
surface  of  membrane. 

3.  The  convoluted  tubular  glands  (D,  Fig.  105),  such  as  the 
kidney  and  testis,  form  another  division.  These  consist  of  tu- 
bules of  membrane,  lined  with  secreting  cells  arranged  like  an 
epithelium.  Through  nearly  the  whole  of  their  long  course, 
the  tubules  present  an  almost  uniform  size  and  structure; 
ultimately  they  terminate  either  in  a  cul-de-sac,  or  by  dilating, 
as  in  the  Malpighian  capsules  of  the  kidney,  or  by  forming  a 
simple  loop  and  returning,  as  in  the  testicle. 

Among  these  varieties  of  structure,  all  the  permanent 
glands  are  alike  in  some  essential  points,  besides  those  which 
they  have  in  common  with  all  truly  secreting  structures.  They 
agree  in  presenting  a  large  extent  of  secreting  surface  within 
a  comparatively  small  space ;  in  the  circumstance  that  while 
one  end  of  the  gland-duct  opens  on  a  free  surface,  the  oppo- 
site end  is  always  closed,  having  no  direct  communication  with 
bloodvessels,  or  any  other  canal ;  and  in  uniform  arrange- 
ment of  capillary  bloodvessels,  ramifying  and  forming  a  net- 
work around  the  walls  and  in  the  interstices  of  the  ducts  and 
acini. 

PROCESS   OF   SECRETION. 

From  what  has  been  said,  it  will  have  already  appeared 
that  the  modes  in  which  secretions  are  produced  are  at  least 
two.  Some  fluids,  such  as  the  secretions  of  serous  membranes, 
appear  to  be  simply  exudations  or  oozings  from  the  bloodves- 
sels, whose  qualities  are  determined  by  those  of  the  liquor  san- 
guinis,  while  the  quantities  are  liable  to  variation,  or  are 
chiefly  dependent  on  the  pressure  of  the  blood  on  the  interior 


322  SECRETION. 

of  the  bloodvessels.  But,  in  the  production  of  the  other  se- 
cretions, such  as  those  of  mucous  membranes  and  all  glands, 
other  besides  these  mechanical  forces  are  in  operation.  Most 
of  the  secretions  are  indeed  liable  to  be  modified  by  the  cir- 
cumstances which  affect  the  simple  exudation  from  the  blood- 
vessels, and  the  products  of  such  exudations,  when  excessive, 
are  apt  to  be  mixed  with  the  more  proper  products  of  all  the  se- 
creting organs.  But  the  act  of  secretion  in  all  glands  is  the 
result  of  the  vital  processes  of  cells  or  nuclei,  which,  as  they 
develop  themselves  and  grow,  form  in  their  interior  the  proper 
materials  of  the  secretion,  and  then  discharge  them. 

The  best  evidence  for  this  view  is :  1st.  That  cells  and 
nuclei  are  constituents  of  all  glands,  however  diverse  their 
outer  forms  and  other  characters,  and  are  in  all  glands  placed 
on  the  surface  or  in  the  cavity  whence  the  secretion  is  poured. 
2d.  That  many  secretions  which  are  visible  with  the  micro- 
scope may  be  seen  in  the  cells  of  their  glands  before  they  are 
discharged.  Thus,  bile  may  be  often  discerned  by  its  yellow 
tinge  in  the  gland-cells  of  the  liver ;  spermatozoids  in  the  cells 
of  the  tubules  of  the  testicles ;  granules  of  uric  acid  in  those 
of  the  kidneys  of  fish  ;  fatty  particles,  like  those  of  milk,  in 
the  cells  of  the  mammary  gland. 

The  process  of  secretion  might,  therefore,  be  said  to  be 
accomplished  in,  and  by  the  life  of,  these  gland-cells.  They 
appear,  like  the  cells  or  other  elements  of  any  other  organ,  to 
develop  themselves,  grow,  and  attain  their  individual  perfec- 
tion by  appropriating  the  nutriment  from  the  adjacent  blood- 
vessels and  elaborating  it  into  the  materials  of  their  walls  and 
the  contents  of  their  cavities.  In  this  perfected  state,  they 
subsist  for  some  brief  time,  and  when  that  period  is  over  they 
appear  to  dissolve  or  burst  and  yield  themselves  and  their  con- 
tents to  the  peculiar  material  of  the  secretion.  And  this  ap- 
pears to  be  the  case  in  every  part  of  the  gland  that  contains 
the  appropriate  gland-cells ;  therefore  not  in  the  extremities  of 
the  ducts  or  in  the  acini  alone,  but  in  great  part  of  their  length. 

In  these  things  there  is  the  closest  resemblance  between 
secretion  and  nutrition  ;  for  if  the  purpose  which  the  secreting 
glands  are  to  serve  in  the  economy  be  disregarded,  their  for- 
mation might  be  considered  as  only  the  process  of  nutrition 
of  organs,  whose  size  and  other  conditions  are  maintained  in, 
and  by  means  of,  the  continual  succession  of  cells  developing 
themselves  and  passing  away.  In  other  words,  glands  are 
maintained  by  the  development  of  the  cells,  and  their  con- 
tinuance in  the  perfect  state ;  and  the  secretions  are  discharged 
as  the  constituent  gland-cells  degenerate  and  are  set  free. 
The  processes  of  nutrition  and  secretion  are  similar,  also,  in 


DISCHARGE    OF    SECRETIONS.  323 

their  obscurity :  there  is  the  same  difficulty  in  saying  why, 
out  of  apparently  the  same  materials,  the  cells  of  one  gland 
elaborate  the  components  of  bile,  while  those  of  another  form 
the  components  of  milk,  and  of  a  third  those  of  saliva,  as  there 
is  in  determining  why  one  tissue  forms  cartilage,  another  bone, 
a  third  muscle,  or  any  other  tissue.  In  nutrition,  also,  as  in 
secretion,  some  elements  of  tissues,  such  as  the  gelatinous  tis- 
sues, are  different  in  their  chemical  properties  from  any  of  the 
constituents  ready-formed  in  the  blood.  Of  these  differences, 
also,  no  account  can  be  rendered ;  but,  obscure  as  the  cause  of 
these  diversities  may  be,  they  are  not  objections  to  the  ex- 
planation of  secretion  as  a  process  similar  to  nutrition ;  an 
explanation  with  which  all  the  facts  of  the  case  are  recon- 
cilable. 

It  may  be  observed  that  the  diversities  presented  by  the 
other  constituents  of  glands  afford  no  explanation  of  the  dif- 
ferences or  peculiarities  of  their  several  products.  There  are 
many  differences  in  the  arrangements  of  the  bloodvessels  in 
different  glands  and  mucous  membranes ;  and,  in  accordance 
with  these,  much  diversity  in  the  rapidity  with  which  the 
blood  traverses  them.  But  there  is  no  reason  for  believing 
that  these  things  do  more  than  influence  the  rate  of  the  pro- 
cess and  the  quantity  of  the  material  secreted.  Cceteris  pari- 
bus,  the  greater  the  vascularity  of  a  secreting  organ,  and  the 
larger  the  supply  of  blood  traversing  its  vessels  in  a  given 
time,  the  larger  is  the  amount  of  secretion ;  but  there  is  no 
evidence  that  the  quantity  or  mode  of  movement  of  the  blood 
can  directly  determine  the  quality  of  the  secretion. 

The  discharge  of  secretions  from  glands  may  take  place  as 
soon  as  they  are  formed;  or  the  secretion  may  be  long  re- 
tained within  the  gland  or  its  ducts.  The  secretion  of  glands 
which  are  continually  in  active  function  for  the  purification 
of  the  blood,  such  as  the  kidneys,  are  generally  discharged 
from  the  gland  as  rapidly  as  they  are  formed.  But  the  secre- 
tions of  those  whose  activity  of  function  is  only  occasional,  such 
as  the  testicle,  are  usually  retained  in  the  ducts  during  the 
periods  of  the  gland's  inaction.  And  there  are  glands  which 
are  like  both  these  classes,  such  as  the  lachrymal  and  salivary, 
which  constantly  secrete  small  portions  of  fluid,  and  on  occa- 
sions of  greater  excitement  discharge  it  more  abundantly. 

When  discharged  into  the  ducts,  the  further  course  of  secre- 
tions is  effected  partly  by  the  pressure  from  behind ;  the  fresh 
quantities  of  secretion  propelling  those  that  were  formed  before. 
In  the  larger  ducts,  its  propulsion  is  assisted  by  the  contraction 
of  their  walls.  All  the  larger  ducts,  such  as  the  ureter  and 
common  bile-duct,  possess  in  their  coats  organic  muscular 


324  SECBETION. 

fibres ;  they  contract  when  irritated,  and  sometimes  manifest 
peristaltic  movements.  Bernard  and  Brown-Sequard,  indeed, 
have  observed  rhythmic  contractions  in  the  pancreatic  and 
bile-ducts,  and  also  in  the  ureters  and  vasa  deferentia.  It  is 
probable  that  the  contractile  power  extends  along  the  ducts  to 
a  considerable  distance  within  the  substance  of  the  glands  whose 
secretions  can  be  rapidly  expelled.  Saliva  and  milk,  for  in- 
stance, are  sometimes  ejected  with  much  force ;  doubtless  by 
the  energetic  and  simultaneous  contraction  of  many  of  the 
ducts  of  their  respective  glands.  The  contraction  of  the  ducts 
can  only  expel  the  fluid  they  contain  through  their  main  trunk ; 
for  at  their  opposite  ends  all  the  ducts  are  closed. 

Circumstances  influencing  Secretion. — The  influence  of  exter- 
nal conditions  on  the  functions  of  glands,  is  manifested  chiefly 
in  alterations  of  the  quantity  of  secretion  ;  and  among  the  prin- 
cipal of  these  conditions  are  variations  in  the  quantity  of  blood, 
in  the  quantity  of  the  peculiar  materials  for  any  secretion  that 
it  may  contain,  and  in  the  conditions  of  the  nerves  of  the 
glands. 

In  general,  an  increase  in  the  quantity  of  blood  traversing 
a  gland,  coincides  with  an  augmentation  of  its  secretion.  Thus, 
the  mucous  membrane  of  the  stomach  becomes  florid  when,  on 
the  introduction  of  food,  its  glands  begin  to  secrete ;  the  mam- 
mary gland  becomes  much  more  vascular  during  lactation ; 
and  it  appears  that  all  circumstances  which  give  rise  to  an  in- 
crease in  the  quantity  of  material  secreted  by  an  organ,  pro- 
duce, coincidently,  an  increased  supply  of  blood.  In  most 
cases,  the  increased  supply  of  blood  rather  follows  than  pre- 
cedes the  increase  of  secretion ;  as,  in  the  nutritive  processes, 
the  increased  nutrition  of  a  part  just  precedes  and  determines 
the  increased  supply  of  blood ;  but,  as  also  in  the  nutritive 
process,  an  increased  supply  of  blood  may  have,  for  a  conse- 
quence, an  increased  secretion  from  the  glands  to  which  it  is 
sent. 

Glands  also  secrete  with  increased  activity  when  the  blood 
contains  more  than  usual  of  the  materials  they  are  designed  to 
separate.  Thus,  when  an  excess  of  urea  is  in  the  blood,  whether 
from  excessive  exercise,  or  from  destruction  of  one  kidney,  a 
healthy  kidney  will  excrete  more  than  it  did  before.  It  will, 
at  the  same  time,  grow  larger :  an  interesting  fact,  as  proving 
both  that  secretion  and  nutrition  in  glands  are  identical,  and 
that  the  presence  of  certain  materials  in  the  blood  may  lead  to 
the  formation  of  structures  in  which  they  may  be  incorporated. 

The  process  of  secretion  is,  also,  largely  influenced  by  the 
condition  of  the  nervous  system. 

The  exact  mode  in  which  the  nervous  system  influences 


THE     DUCTLESS    GLANDS.  325 

secretion  must  be  still  regarded  as  somewhat  obscure.  In  part, 
it  exerts  its  influence  by  increasing  or  diminishing  the  quantity 
of  blood  supplied  to  the  secreting  gland,  in  virtue  of  the  power 
which  it  exercises  over  the  contractility  of  the  smaller  blood- 
vessels ;  while  it  also  has  a  more  direct  influence  analogous  to 
the  trophic  influence  referred  to  in  the  chapter  on  Nutrition. 
Its  influence  over  secretion,  as  well  as  over  other  functions  of 
the  body,  may  be  excited  by  causes  acting  directly  upon  the 
nervous  centres,  upon  the  nerves  going  to  the  secreting  organ, 
or  upon  the  nerves  of  other  parts.  In  the  latter  case,  a  reflex 
action  is  produced :  thus  the  impression  produced  upon  the 
nervous  centres  by  the  contact  of  food  in  the  mouth,  is  reflected 
upon  the  nerves  supplying  the  salivary  glands,  and  produces, 
through  these,  a  more  abundant  secretion  of  saliva. 

Through  the  nerves,  various  conditions  of  the  mind  also  in- 
fluence the  secretions.  Thus,  the  thought  of  food  may  be  suf- 
ficient to  excite  an  abundant  flow  of  saliva.  And,  probably, 
it  is  the  mental  state  which  excites  the  abundant  secretion  of 
urine  in  hysterical  paroxysms,  as  well  as  the  perspirations  and, 
occasionally,  diarrhoea,  which  ensue  under  the  influence  of 
terror,  and  the  tears  excited  by  sorrow  or  excess  of  joy.  The 
quality  of  a  secretion  may  also  be  affected  by  the  mind ;  as  in 
the  cases  in  which,  through  grief  or  passion,  the  secretion  of 
milk  is  altered,  and  is  sometimes  so  changed  as  to  produce 
irritation  in  the  alimentary  canal  of  the  child,  or  even  death 
(Carpenter). 

The  secretions  of  some  of  the  glands  seem  to  bear  a  certain 
relation  or  antagonism  to  each  other,  by  which  an  increased 
activity  of  one  is  usually  followed  by  diminished  activity  of 
one  or  more  of  the  others  ;  and  a  deranged  condition  of  one  is 
apt  to  entail  a  disordered  state  in  the  others.  Such  relations 
appear  to  exist  among  the  various  mucous  membranes :  and 
the  close  relation  between  the  secretion  of  the  kidney  and  that 
of  the  skin  is  a  subject  of  constant  observation. 


CHAPTER  XIII. 

THE   VASCULAR    GLANDS;    OR    GLANDS    WITHOUT    DUCTS. 

THE  materials  separated  from  the  blood  by  the  ordinary 
process  of  secretion  by  glands,  are  always  discharged  from  the 
organ  in  which  they  are  formed,  and  either  straightway  ex- 

28 


326  THE    DUCTLESS    GLANDS. 

pelled  from  the  body,  or  if  they  are  again  received  into  the 
blood,  it  is  only  after  they  have  been  altered  from  their  original 
condition,  as  in  the  cases  of  the  saliva  and  bile.  There  ap- 
pears, however,  to  be  a  modification  of  the  process  of  secre- 
tion, in  which  certain  materials  are  abstracted  from  the  blood, 
undergo  some  change,  and  are  added  to  the  lymph  or  restored 
to  the  blood,  without  being  previously  discharged  from  the 
secreting  organ,  or  made  use  of  for  any  secondary  purpose. 
The  bodies  in  which  this  modified  form  of  secretion  takes  place, 
are  usually  described  as  vascular  glands,  or  glands  without 
ducts,  and  include  the  spleen,  the  thymus  and  thyroid  glands, 
the  supra-renal  capsules,  and,  according  to  (Esterlin  and  Ecker 
and  Gull,  the  pineal  gland  and  pituitary  body ;  possibly,  also 
the  tonsils. 

The  solitary  and  agminate  glands  of  the  intestine  (p.  242), 
and  lymph-glands  in.general,  also  closely  resemble  them  ;  in- 
deed, both  in  structure  and  function,  the  vascular  glands  bear 
a  close  relation,  on  the  one  hand,  to  the  true  secreting  glands, 
and  on  the  other,  to  the  lymphatic  glands. 

The  evidence  in  favor  of  the  view  that  these  organs  exercise 
a  function  analogous  to  that  of  secreting  glands,  has  been 

FIG.  106. 


Vesicles  from  the  thyroid  gland  of  a  child  (from  Kolliker)  25.  o  _    a,  connective  tissue 
between  the  vesicles ;  b,  capsule  of  the  vesicles ;  c,  their  epithelial  lining. 

chiefly  obtained  from  investigations  into  their  structure,  which 
have  shown  that  most  of  the  glands  without  ducts  contain  the 
same  essential  structures  as  the  secreting  glands,  except  the 
ducts.  They  are  mainly  composed  of  vesicles,  or  sacculi,  either 
simple  and  closed,  as  in  the  thyroid  (Fig.  106),  and  supra- 


THE    DUCTLESS    GLANDS.  327 

renal  capsules,  or  variously  branched,  and  with  the  cavities  of 
the  several  branches  communicating  in  and  by  common  canals, 
as  in  the  thy m us  (Fig.  107).  These  vesicles,  like  the  acini  of 
secreting  glands,  are  formed  of  a  delicate  homogeneous  mem- 
brane, are  surrounded  with  and  often  traversed  by  a  vascular 
plexus,  and  are  filled  with  finely  molecular  albuminous  fluid, 
suspended  in  which  are  either  granules  of  fat,  or  cytoblasts,  or 
nuclei,  or  nucleated  cells,  or  a  mixture  of  all  these. 

Structure  of  the  Spleen. — The  spleen  is  covered  externally 
almost  completely  by  a  serous  coat  derived  from  the  peri- 
toneum, while  within  this  is  the  proper  fibrous  coat  or  capsule 
of  the  organ.  The  latter,  composed  of  connective  tissue,  with 

FIG.  107. 


Transverse  section  of  a  lobule  of  an  injected  infantile  thyinus  gland  (after  K61- 
liker)  (magnified  30  diameters),  a,  capsule  of  connective  tissue  surrounding  the 
lobule ;  ft,  membrane  of  the  glandular  vesicles ;  c,  cavity  of  the  lobule,  from  which 
the  larger  bloodvessels  are  seen  to  extend  towards  and  ramify  in  the  spheroidal 
masses  of  the  lobule. 

a  large  preponderance  of  elastic  fibres,  forms  the  immediate 
investment  of  the  spleen.  Prolonged  from  its  inner  surface  are 
fibrous  processes  or  trabeculce,  which  enter  the  interior  of  the 
organ,  and,  dividing  and  anastomosing  in  all  parts,  form  a 
kind  of  supporting  framework  or  stroma,  in  the  interstices  of 
which  the  proper  substance  of  the  spleen,  or  the  spleen-pulp,  is 
contained.  At  the  hilus  of  the  spleen,  or  the  part  at  which 


328  THE     DUCTLESS    GLANDS. 

the  bloodvessels,  nerves,  and  lymphatics  enter,  the  fibrous  coat 
is  prolonged  into  the  spleen-substance  in  the  form  of  investing 
sheaths  for  the  arteries  and  veins,  which  sheaths  again  are  con- 
nected with  the  trabeculcv  before  referred  to. 

The  spleen-pulp,  which  is  of  a  dark  red  or  reddish-brown 
color,  is  composed  chiefly  of  cells.  Of  these,  some  are  granular 
corpuscles  resembling  the  lymph-corpuscles,  both  in  general 
appearance  and  in  being  able  to  perform  amoeboid  movements; 
others  are  red  blood-corpuscles  of  normal  appearance  or  vari- 
ously changed ;  while  there  are  also  large  cells  containing 
either  pigment  allied  to  the  coloring  matter  of  the  blood,  or 
rounded  corpuscles  like  red  blood-cells. 

The  splenic  artery,  which  enters  the  spleen  by  its  concave 
surface  or  hilus,  divides  and  subdivides,  with  but  little  anas- 
tomosis between  its  branches,  in  the  midst  of  the  spleen-pulp, 
at  the  same  time  that  its  branches  are  sheathed,  as  before  said, 
by  the  fibrous  coat,  which  they,  so  to  speak,  carry  into  the 
spleen  with  them.  Ending  in  capillaries,  they  either  com- 
municate, as  in  other  parts  of  the  body,  with  the  radicles  of 
the  veins,  or  end  in  lacunar  spaces  in  the  spleen-pulp,  from 
which  veins  arise  (Gray). 

On  the  face  of  a  section  of  the  spleen  can  be  usually  seen, 
readily  with  the  naked  eye,  minute,  scattered,  rounded  or  oval 
whitish  spots,  mostly  from  ^  to  g1^  inch  in  diameter.  These 
are  the  Malpighian  corpuscles  of  the  spleen,  and  are  situated  on 
the  sheaths  of  the  minute  splenic  arteries,  of  which,  indeed, 
they  may  be  said  to  be  outgrowths  (Fig.  108).  For  while  the 
sheaths  of  the  larger  arteries  are  constructed  of  ordinary  con- 
nective tissue,  this  has  become  modified  where  it  forms  an  in- 
vestment for  the  smaller  vessels,  so  as  to  be  a  fine  retiform 
tissue,  with  abundance  of  corpuscles,  like  lymph-corpuscles, 
contained  in  its  meshes ;  and  the  Malpighian  corpuscles  are 
but  small  outgrowths  of  this  cytogenous  or  cell-bearing  connec- 
tive tissue.  They  are  composed  of  masses  of  corpuscles,  inter- 
sected iu  all  parts  by  a  delicate  fibrillar  tissue,  which,  though 
it  invests  the  Malpighian  bodies,  does  not  form  a  complete 
capsule.  Blood-capillaries  traverse  the  Malpighian  corpuscles 
and  form  a  plexus  in  their  interior.  The  structure  of  a  Mal- 
pighian corpuscle  of  the  spleen  is,  therefore,  very  similar  to 
that  of  lymphatic-gland  substance  (p.  284). 

The  general  resemblances  in  structure  between  certain  of 
the  vascular  glands  and  the  true  glands  lead  to  the  supposition 
that  both  sets  of  organs  pursue,  up  to  a  certain  point,  a  similar 
course  in  the  discharge  of  their  functions.  It  is  assumed  that 
certain  principles  in  an  inferior  state  of  organization  are  effused 


FUNCTIONS    OF    DUCTLESS    GLANDS.          329 

from  the  vessels  into  the  sacculi,  arid  gradually  develop  into 
nuclei  or  cytoblasts,  which  may  be  further  developed  into  cells  ; 
that  in  the  growth  of  these  nuclei  and  cells,  the  materials  de- 

FIG.  108. 


The  figure  shows  a  portion  of  a  small  artery,  to  one  of  the  twigs  of  which  the 
Malpighian  corpuscles  are  attached. 

rived  from  the  blood  are  elaborated  into  a  higher  condition  of 
organization  ;  and  that  when  liberated  by  the  dissolution  of 
these  cells,  they  pass  into  the  lymphatics,  or  are  again  received 
into  the  blood,  whose  aptness  for  nutrition  they  contribute  to 
maintain. 

The  opinion  that  the  vascular  glands  thus  serve  for  the 
higher  organization  of  the  blood,  is  supported  by  their  being 
all  especially  active  in  the  discharge  of  their  functions  during 
foetal  life  and  childhood,  when,  for  the  development  and 
growth  of  the  body,  the  most  abundant  supply  of  highly  or- 
ganized blood  is  necessary.  The  bulk  of  the  thymus  gland,  in 
proportion  to  that  of  the  body,  appears  to  bear  almost  a  direct 
proportion  to  the  activity  of  the  body's  development  and 
growth,  and  when,  at  the  period  of  puberty,  the  development 
of  the  body  may  be  said  to  be  complete,*the  gland  wastes,  and 
finally  disappears.  The  thyroid  gland  and  supra-renal  cap- 
sules, also,  though  they  probably  never  cease  to  discharge  some 


330  THE     DUCTLESS    GLANDS. 

amount  of  function,  yet  are  proportionally  much  smaller  in 
childhood  than  in  foetal  life  and  infancy ;  and  with  the  years 
advancing  to  the  adult  period,  they  diminish  yet  more  in  pro- 
portionate size  and  apparent  activity  of  function.  The  spleen 
more  nearly  retains  its  proportionate  size,  and  enlarges  nearly 
as  the  whole  body  does. 

The  function  of  the  vascular  glands  seems  not  essential  to 
life,  at  least  not  in  the  adult.  The  thymus  wastes  and  dis- 
appears ;  no  signs  of  illness  attend  some  of  the  diseases  which 
wholly  destroy  the  structure  of  the  thyroid  gland ;  and  the 
spleen  has  been  often  removed  in  animals,  and  in  a  few  in- 
stances in  men,  without  any  evident  ill-consequence.  It  is 
possible  that,  in  such  cases,  some  compensation  for  the  loss  of 
one  of  the  organs  may  be  afforded  by  an  increased  activity  of 
function  in  those  that  remain.  The  experiment,  to  be  com- 
plete, should  include  the  removal  of  all  these  organs,  an  opera 
tion  of  course  not  possible  without  immediate  danger  to  life. 
Nor,  indeed,  would  this  be  certainly  sufficient,  since  there  is 
reason  to  suppose  that  the  duties  of  the  spleen,  after  its  re- 
moval, might  be  performed  by  lymphatic  glands,  between 
whose  structure  and  that  of  the  vascular  glands  there  is  much 
resemblance,  and  which,  it  is  said,  have  been  found  peculiarly 
enlarged  when  the  spleen  has  been  removed  (Meyer). 

Although  the  functions  of  all  the  vascular  glands  may  be 
similar,  in  so  far  as  they  may  all  alike  serve  for  the  elabora- 
tion and  maintenance  of  the  blood,  yet  each  of  them  probably 
discharges  a  peculiar  office,  in  relation  either  to  the  whole 
economy,  or  to  that  of  some  other  organ.  Respecting  the 
special  office  of  the  thyroid  gland,  nothing  reasonable  can  be 
suggested  ;  nor  is  there  any  certain  evidence  concerning  that 
of  the  supra-renal  capsules.1  Respecting  the  thymus  gland, 
the  observations  of  Mr.  Simon,  confirmed  by  those  of  Friedle- 
ben  and  others,  have  shown  that  in  the  hibernating  animals, 
in  which  it  exists  throughout  life,  as  each  successive  period  of 
hibernation  approaches,  the  thymus  greatly  enlarges  and  be- 
comes laden  with  fat,  which  accumulates  in  it  and  in  fat- 
glands  connected  with  it,  in  even  larger  proportions  than  it 
does  in  the  ordinary  seats  of  adipose  tissue.  Hence  it  appears 


1  Mr.  J.  Hutchinson,  and  more  recently,  Dr.  Wilks,  following  out 
Dr.  Addison's  discovery,  have,  by  the  collection  of  a  large  and  valua- 
ble series  of  cases  in  which  the  supra-renal  capsules  were  diseased, 
demonstrated  most  sati>f'actorily  the  very  close  relation  subsisting  be- 
tween disease  of  these  organs  and  brown  discoloration  of  the  skin; 
but  the  explanation  of  this  relation  is  still  involved  in  obscurity,  and 
consequently  does  not  aid  much  in  determining  the  functions  of  the 
supra-renal  capsules. 


FUNCTIONS    OF    SPLEEN.  331 

to  serve  for  the  storing  up  of  materials  which,  being  reabsorbed 
in  the  inactivity  of  the  hibernating  period,  may  maintain  the 
respiration  and  the  temperature  of  the  body  in  the  reduced 
state  to  which  they  fall  during  that  time. 

With  respect  to  the  office  of  the  spleen,  we  have  somewhat 
more  definite  information.  In  the  first  place,  the  large  size 
which  it  gradually  acquires  towards  the  termination  of  the 
digestive  process,  and  the  great  increase  observed  about  this 
period  in  the  amount  of  the  finely-granular  albuminous  plasma 
within  its  parenchyma,  and  the  subsequent  gradual  decrease 
of  this  material,  seem  to  indicate  that  this  organ  is  concerned 
in  elaborating  the  albuminous  or  formative  materials  of  food, 
and  for  a  time  storing  them  up,  to  be  gradually  introduced 
iiito  the  blood,  according  to  the  demands  of  the  general  system. 
The  small  amount  of  fatty  matter  in  such  plasma,  leads  to  the 
inference  that  the  gland  has  little  to  do  in  regard  to  the  prepa- 
ration of  material  for  the  respiratory  process. 

Then  again,  it  seems  not  improbable  that,  as  Hewson  origi- 
nally suggested,  the  spleen,  and  perhaps  to  some  extent  the 
other  vascular  glands,  are,  like  the  lymphatic  glands,  engaged 
in  the  formation  of  the  germs  of  subsequent  blood-corpuscles. 
For  it  seems  quite  certain,  that  the  blood  of  the  splenic  vein 
contains  an  unusually  large  amount  of  white  corpuscles ;  and 
in  the  disease  termed  leucocythsemia,  in  which  the  pale  cor- 
puscles of  the  blood  are  remarkably  increased  in  number, 
there  is  almost  always  found  an  hypertrophied  state  of  the 
spleen  or  thyroid  body,  or  some  of  the  lymphatic  glands. 
Accordingly  there  seems  to  be  a  close  analogy  in  function  be- 
tween the  so-called  vascular  and  the  lymphatic  glands :  the 
former  elaborating  albuminous  principles,  and  forming  the 
germs  of  new  blood-corpuscles  out  of  alimentary  materials 
absorbed  by  the  bloodvessels  ;  the  latter  discharging  the  like 
office  on  nutritive  materials  taken  up  by  the  general  absorbent 
system.  In  Kolliker's  opinion,  the  development  of  colorless 
and  also  colored  corpuscles  of  the  blood  is  one  of  the  essential 
functions  of  the  spleen,  into  the  veins  of  which  the  new-formed 
corpuscles  pass,  and  are  thus  conveyed  into  the  general  cur- 
rent of  the  circulation. 

There  is  reason  to  believe,  too,  that  in  the  spleen  many  of 
the  red  corpuscles  of  the  blood,  those  probably  which  have 
discharged  their  office  and  are  worn  out,  undergo  disintegra- 
tion ;  for  in  the  colored  portion  of  the  spleen-pulp  an  abun- 
dance of  such  corpuscles,  in  various  stages  of  degeneration, 
are  found,  while  the  red  corpuscles  in  the  splenic  venous  blood 
are  said  to  be  relatively  diminished.  According  to  Kolliker's 
description  of  this  process  of  disintegration,  the  blood-corpus- 


332  THE    SKIN. 

cles,  becoming  smaller  and  darker,  collect  together  in  roundish 
heaps,  which  may  remain  in  this  condition,  or  become  each 
surrounded  by  a  cell-wall.  The  cells  thus  produced  may  con- 
tain from  one  to  twenty  blood-corpuscles  in  their  interior. 
These  corpuscles  become  smaller  and  smaller ;  exchange  their 
red  for  a  golden  yellow,  brown,  or  black  color ;  and,  at  length 
are  converted  into  pigment-granules,  which  by  degrees  become 
paler  and  paler,  until  all  color  is  lost.  The  corpuscles  undergo 
these  changes  whether  the  heaps  of  them  are  enveloped  by  a 
cell-wall  or  not. 

Besides  these,  its  supposed  direct  offices,  the  spleen  is  be- 
lieved to  fulfil  some  purpose  in  regard  to  the  portal  circula- 
tion, with  which  it  is  in  close  connection.  From  the  readiness 
with  which  it  admits  of  being  distended,  and  from  the  fact 
that  it  is  generally  small  while  gastric  digestion  is  going  on, 
and  enlarges  when  that  act  is  concluded,  it  is  supposed  to  act 
as  a  kind  of  vascular  reservoir,  or  diverticulum  to  the  portal 
system,  or  more  particularly  to  the  vessels  of  the  stomach. 
That  it  may  serve  such  a  purpose  is  also  made  probable  by  the 
enlargement  which  it  -undergoes  in  certain  affections  of  the 
heart  and  liver,  attended  with  obstruction  to  the  passage  of 
blood  through  the  latter  organ,  and  by  its  diminution  when 
the  congestion  of  the  portal  system  is  relieved  by  discharges 
from  the  bowels,  or  by  the  effusion  of  blood  into  the  stomach. 
This  mechanical  influence  on  the  circulation,  however,  can 
hardly  be  supposed  to  be  more  than  a  very  subordinate  part 
of  the  office  of  an  organ  of  so  great  complexity  as  the  spleen, 
and  containing  so  many  other  structures  besides  bloodvessels. 
The  same  may  also  be  said  with  regard  to  the  opinion  that  the 
thyroid  gland  is  important  as  a  diverticulum  for  the  cerebral 
circulation,  or  the  thymus  for  the  pulmonary  in  childhood. 
These,  like  the  spleen,  must  have  peculiar  and  higher,  though 
as  yet  ill-understood,  offices. 


CHAPTER  XIV. 

THE   SKIN   AND   ITS   SECRETIONS. 

To  complete  the  consideration  of  the  processes  of  organic 
life,  an4  especially  of  those  which,  by  separating  materials 
from  the  blood,  maintain  it  in  the  state  necessary  for  the 
nutrition  of  the  body,  the  structure  and  fuuctions  of  the  skin 
must  be  now  considered :  for  besides  the  purposes  which  it 
serves — (1),  as  an  internal  integument  for  the  protection  of 


EPIDERMIS. 


333 


the  deeper  tissues,  and  (2),  as  a  sensitive  organ  in  the  exercise 
of  touch,  it  is  also  (3),  an  important  excretory,  and  (4)  an 
absorbing  organ  ;  while  it  plays  a  most  important  part  in  (5) 
the  regulation  of  the  temperature  of  the  body. 

Structure  of  the  Skin. 

The  skin  consists,  principally,  of  a  layer  of  vascular  tissue, 
named  the  corium,  derma,  or  cutis  vera,  and  an  external  cover- 
ing of  epithelium  termed  the  cuticle  or  epidermis.  Within 
and  beneath  the  corium  are  imbedded  several  organs  with 
special  functions,  namely,  sudoriparous  glands,  sebaceous  glands, 
and  hair-follicles ;  and  on  its  surface  are  sensitive  papillae.  The 
so-called  appendages  of  the  skin — the  hair  and  noils — are  modi- 
fications of  the  epidermis. 

Epidermis. — The  epidermis  is  composed  of  several  layers  of 
epithelial  cells  of  the  squamous  kind  (p.  34),  the  deeper  cells, 
however,  being  rounded  or  elongated,  and  in  the  latter  in- 
stance having  their  long  axis  arranged  vertically  as  regards 
the  general  surface  of  the  skin,  while  the  more  superficial  cells 
are  flattened  and  scaly 
(Fig.  109).  The  deeper  FIG.  109. 

part  of  the  epidermis, 
which  is  softer  and  more 
opaque  than  the  super- 
ficial, is  called  the  rete 
mucosum.  Many  of  the 
epidermal  cells  contain 
pigment,  and  the  varying 
quantity  of  this  is  the 
source  of  the  different 
shades  of  tint  in  the  skin, 
both  of  individuals  and 
races.  The  coloring  mat- 
ter is  contained  chiefly  in 
the  deeper  cells  composing 
the  rete  mucosum,  and  be- 
comes less  evident  in  them 
as  they  are  gradually 
pushed  up  by  those  under 

Lj    J-t  1-1  Skin  of  the  negro,  in  a  vertical  section,  mag- 

them,   and    become,    like   nified  250diameters.   «,«,  cutaneous  papiii* ; 

their  predecessors,  flat-  b>  umiermost  and  dark-colored  layer  of  oblong 
tened  and  Scale-like  (Fig.  vertical  epidermis  cells;  c,  mucous  or  Malpig- 
109).  It  is  by  this  pro-  Wan  layer ;  d,  horny  layer  (from  Sharpey). 

cess   of    production    from 

beneath,  to  make  up  for  the  waste  at  the  surface,  that   the 

growth  of  the  cuticle  is  effected. 


334  THE    SKIN. 

The  thickness  of  the  epidermis  on  different  portions  of  the 
skin  is  directly  proportioned  to  the  friction,  pressure,  and 
other  sources  of  injury  to  which  it  is  exposed;  and  the  more  it 
is  subjected  to  such  injury,  within  certain  limits,  the  more 
does  it  grow,  and  the  thicker  and  more  horny  does  it  become ; 
for  it  serves  as  well  to  protect  the  sensitive  and  vascular  cutis 
from  injury  from  without,  as  to  limit  the  evaporation  of  fluid 
from  the  bloodvessels.  The  adaptation  of  the  epidermis  to 
the  latter  purposes  may  be  well  shown  by  exposing  to  the  air 
two  dead  hands  or  feet,  of  which  one  has  its  epidermis  perfect, 
and  the  other  is  deprived  of  it ;  in  a  day,  the  skin  of  the  lat- 
ter will  become  brown,  dry,  and  horn-like,  while  that  of  the 
former  will  almost  retain  its  natural  moisture. 

Cutis  vera. — The  corium  or  cutis,  which  rests  upon  a  layer  of 
adipose  and  cellular  tissue  of  varying  thickness,  is  a  dense  and 
tough,  but  yielding  and  highly  elastic  structure,  composed  of 
fasciculi  of  fibre-cellular  tissue,  interwoven  in  all  directions, 
and  forming,  by  their  interlacements,  numerous  spaces  or 
areolae.  These  areolae  are  large  in  the  deeper  layers  of  the 
cutis,  and  are  there  usually  filled  with  little  masses  of  fat  (Fig. 
112) :  but,  in  the  more  superficial  parts,  they  are  exceedingly 
small  or  entirely  obliterated. 

By  means  of  its  toughness,  flexibility,  and  elasticity,  the  skin 
is  eminently  qualified  to  serve  as  the  general  integument  of  the 
body,  for  defending  the  internal  parts  from  external  violence, 
and  readily  yielding  and  adapting  itself  to  their  various  move- 
ments and  changes  of  position.  But,  from  the  abundant  sup- 
ply of  sensitive  nerve-fibres  which  it  receives,  it  is  enabled  to 
fulfil  a  not  less  important  purpose  in  serving  as  the  principal 
organ  of  the  sense  of  touch.  The  entire  surface  of  the  skin  is 
extremely  sensitive,  but  its  tactile  properties  are  due  chiefly  to 
the  abundant  papillae  with  which  it  is  studded.  These  papillae 
are  conical  elevations  of  the  corium,  with  a  single  or  divided 
free  extremity,  more  prominent  and  more  densely  set  at  some 
parts  than  at  others  (Figs.  110  and  111).  The  parts  on  which 
they  are  most  abundant  and  most  prominent  are  the  palmar 
surface  of  the  hands  and  fingers,  and  the  soles  of  the  feet — 
parts,  therefore,  in  which  the  sense  of  touch  is  most  acute. 
On  these  parts  they  are  disposed  in  double  rows,  in  parallel 
curved  lines,  separated  from  each  other  by  depressions  (Fig. 
112).  Thus  they  may  be  seen  easily  on  the  palm,  whereon 
each  raised  line  is  composeed  of  a  double  row  of  papillae,  and 
is  intersected  by  short  transverse  lines  or  furrows  corresponding 
with  the  interspaces  between  the  successive  pairs  of  papillae. 
Over  other  parts  of  the  skin  they  are  more  or  less  thinly  scat- 
tered, and  are  scarcely  elevated  above  the  surface.  Their 


THE    CORIUM    OK    CUTIS    VERA. 


335 


average  length  is  about  T-J0th  of  an  inch,  and  at  their  base 
they  measure  about  ^th  of  an  inch  in  diameter.     Each  pa- 


FlG.   Ill 


FIG.  110.— Papilla,  as  seen  with  a  microscope,  on  a  portion  of  the  true  skin,  from 
which  the  cuticle  has  been  removed  (after  Breschet). 

FIG.  111.— Compound  papillse  from  the  palm  of  the  hand,  magnified  60  diameters  ; 
a.  basis  of  a  papilla ;  ft,  b,  divisions  or  branches  of  the  same ;  c,  c,  branches  belonging 
to  papillse,  of  which  the  bases  are  hidden  from  view  (after  Kolliker). 

FIG.  112. 


Vertical  section  of  the  skin  and  subcutaneous  tissue,  from  end  of  the  thumb,  across 
the  ridges  and  furrows,  magnified  20  diameters  (from  Kolliker) :  a,  horny,  and  b, 
mucous  layer  of  the  epidermis ;  c,  corium;  d,  panniculus  adiposus;  e,  papilla;  on  the 
ridges ;  /,  fat  clusters ;  g,  sweat-glands  ;  h,  sweat-ducts ;  i,  their  openings  on  the 
surface. 


336 


THE    SKIN. 


pilla  is  abundantly  supplied  with  blood,  receiving  from  the 
vascular  plexus  in  the  cutis  one  or  more  minute  arterial  twigs, 
which  divide  into  capillary  loops  in  its  substance,  and  then 
reunite  into  a  minute  vein,  which  passes  out  at  its  base.  The 
abundant  supply  of  blood  which  the  papillae  thus  receive  ex- 
plains the  turgescence  or  kind  of  erection  which  they  undergo 
when  the  circulation  through  the  skin  is  active.  The  majority, 
but  not  all,  of  the  papillae  contain  also  one  or  more  terminal 
nerve-fibres,  from  the  ultimate  ramifications  of  the  cutaneous 
plexus  on  which  their  exquisite  sensibility  depends.  The  exact 
mode  in  which  these  nerve-fibres  terminate  is  not  yet  satisfac- 
torily determined.  In  some  parts,  especially  those  in  which 
the  sense  of  touch  is  highly  developed,  as,  for  example,  the 
palm  of  the  hand  and  the  lips,  the  fibres  appear  to  terminate, 
in  many  of  the  papillae,  by  one  or  more  free  ends  in  the  sub- 
stance of  a  dilated  oval-shaped  body,  not  unlike  a  Paciniau 
corpuscle  (Figs.  136,  137),  occupying  the  principal  part  of  the 
interior  of  the  papillae,  and  termed  a  touch-corpuscle  (Fig;  113). 


FIG.  113. 


Papillse  from  the  skin  of  the  hand,  freed  from  the  cuticle  and  exhibiting  the  tac- 
tile corpuscles.  Magnified  350  diameters.  A.  Simple  papilla  with  four  nerve-fibres: 
a,  tactile  corpuscle  ;  b,  nerves.  B.  Papilla  treated  with  acetic  acid :  a,  cortical  layer 
with  cells  and  fine  elastic  filaments  ;  b,  tactile  corpuscle  with  transverse  nuclei ;  c, 
entering  nerve  with  neurilemma  or  perineurium  ;  d,  nerve-fibres  winding  round  the 
corpuscle,  c.  Papilla  viewed  from  above  so  as  to  appear  as  a  cross-section :  o,  corti- 
cal layer;  b,  nerve-fibre;  c,  sheath  of  the  tactile  corpuscle  containing  nuclei;  d, 
core  (after  Kolliker). 

The  nature  of  this  body  is  obscure.  Kolliker,  Huxley,  and 
others,  regard  it  as  little  else  than  a  mass  of  fibrous  or  con- 
nective tissue,  surrounded  by  elastic  fibres,  and  formed,  accord- 
ing to  Huxley,  by  an  increased  development  of  the  neurilemma 


TOUCH-CORPUSCLES END-BULBS.  *       337 


of  the  nerve-fibres  entering  the  papillae.  Wagner,  however,  to 
whom  seems  to  belong  the  merit  of  first  fully  describing  these 
bodies,  believes  that,  instead  of  thus  consisting  of  a  homogene- 
ous mass  of  connective-tissue,  they  are  special  and  peculiar 
bodies  of  laminated  structure,  directly  concerned  in  the  sense 
of  touch.  They  do  not  occur  in  all  the  papillae  of  the  parts 
where  they  are  found,  and,  as  a  rule,  in  the  papillae  in  which 
they  are  present  there  are  no  bloodvessels.  Since  these  pecu- 
liar bodies  in  which  the  nerve-fibres  end  are  only  met  with  in 
the  papillae  of  highly  sensitive  parts,  it  may  be  inferred  that 
they  are  specially  concerned  in  the  sense  of  touch,  yet  their 
absence  from  the  papillae  of  other  tactile  parts  shows  that  they 
are  not  essential  to  this  sense. 

Closely  allied  in  structure  to  the  Pacinian  corpuscles  and 
touch-corpuscles  are  some  little  bodies  about  g^0  of  an  inch  in 
diameter,  first  particularly  described  by  Krause,  and  named 
by  him  "  end-bulbs."  They  are  generally  oval  or  spheroidal, 
and  composed  externally  of  a  coat  of  connective  tissue  inclos- 
ing a  softer  matter,  in  which  the  extremity  of  a  nerve  termin- 
ates. These  bodies  have  been  found  chiefly  in  the  lips,  tongue, 
palate,  and  the  skin  of  the  glans  penis  (Fig.  114). 


FIG.  114. 


End-bulbs  in  papillae  (magnified)  treated  with  acetic  acid.  A,  from  the  lips  ;  the 
white  loops  in  one  of  them  are  capillaries.  B,  from  the  tongue.  Two  end-bulbs  seen 
in  the  midst  of  the  simple  papillae:  a,  a,  nerves  (from  Kolliker). 

Although  destined  especially  for  the  sense  of  touch,  the 
papillae  are  not  so  placed  as  to  come  into  direct  contact  with 
external  objects  ;  but,  like  the  rest  of  the  surface  of  the  skin, 


338  THE    SKIN. 

are  covered  by  one  or  more  layers  of  epithelium,  forming  the 
cuticle  or  epidermis.  The  papillae  adhere  very  intimately  to 
the  cuticle,  which  is  thickest  in  the  spaces  between  them,  but 
tolerably  level  on  its  outer  surface :  hence,  when  stripped  off 
from  the  cutis,  as  after  maceration,  its  internal  surface  presents 
a  series  of  pits  and  elevations  corresponding  to  the  papillae  and 
their  interspaces,  of  which  it  thus  forms  a  kind  of  mould. 
Besides  affording  by  its  impermeability  a  check  to  undue 
evaporation  from  the  skin,  and  providing  the  sensitive  cutis 
with  a  protecting  investment,  the  cuticle  is  of  service  in  rela- 
tion to  the  sense  of  touch.  For,  by  being  thickest  in  the 
spaces  between  the  papilla,  and  only  thinly  spread  over  the 
summits  of  these  processes,  it  may  serve  to  subdivide  the  sen- 
tient surface  of  the  skin  into  a  number  of  isolated  points,  each 
of  which  is  capable  of  receiving  a  distinct  impression  from  an 
external  bodies.  By  covering  the  papillae  it  renders  the  sensa- 
tion produced  by  external  bodies  more  obtuse,  and  in  this 
manner  also  is  subservient  to  touch  :  for  unless  the  very  sensi- 
tive papillae  were  thus  defended,  the  contact  of  substances 
would  give  rise  to  pain,  instead  of  the  ordinary  impressions  of 
touch.  This  is  shown  in  the  extreme  sensitiveness  and  loss  of 
tactile  power  in  a  part  of  the  skin  when  deprived  of  its  epi- 
dermis. If  the  cuticle  is  very  thick,  however,  as  on  the  heel, 
touch  becomes  imperfect,  or  is  lost,  through  the  inability  of 
the  tactile  papillae  to  receive  impressions  through  the  dense  and 
horny  layer  covering  them. 

Sudoriparous  Glands. — In  the  middle  of  each  of  the  trans- 
verse furrows  between  the  papillae,  and  irregularly  scattered 
between  the  bases  of  the  papillae  in  those  parts  of  the  surface 
of  the  body  in  which  there  are  no  furrows  between  them,  are 
the  orifices  of  ducts  of  the  sudoriparous  or  sweat  glands,  by 
which  it  is  probable  that  a  large  portion  of  the  aqueous  and 
gaseous  materials  excreted  by  the  skin  are  separated.  Each 
of  these  glands  consists  of  a  small  lobular  mass,  which  appears 
formed  of  a  coil  of  tubular  gland-duct,  surrounded  by  blood- 
vessels and  imbedded  in  the  subcutaneous  adipose  tissue  (Fig. 
112).  From  this  mass,  the  duct  ascends,  for  a  short  distance,  in 
a  spiral  manner  through  the  deeper  part  of  the  cutis,  then  pass- 
ing straight,  and  then  sometimes  again  becoming  spiral,  it 
passes  through  the  cuticle  and  opens  by  an  oblique  valve- 
like  aperture.  In  the  parts  where  the  epidermis  is  thin,  the 
ducts  themselves  are  thinner  and  more  nearly  straight  in  their 
course  (Fig.  115).  The  duct,  which  maintains  nearly  the  same 
diameter  throughout,  is  lined  with  a  layer  of  epithelium  con- 
tinuous with  the  epidermis  ;  while  the  part  which  passes  through 
the  epidermis  is  composed  of  the  latter  structure  only ;  the 


SEBACEOUS    GLANDS.  339 

cells  which  immediately  form  the  boundary  of  the  canal  in  this 
part  being  somewhat  differently  arranged  from  those  of  the 
adjacent  cuticle. 

The  sudoriparous  glands  are  abundantly  distributed  over 
the  whole  surface  of  the  body  ;  but  are  especially  numerous,  as 
well  as  very  large,  in  the  skin  of  the  palm  of  the  hand, 
where,  according  to  Krause,  they  amount  to  2736  in  each  su- 
perficial square  inch,  and  according  to  Mr.  Erasmus  Wilson, 
to  as  many  as  3528.  They  are  almost  equally  abundant  and 
large  in  the  skin  of  the  sole.  The  glands  by  which  the  pecu- 
liar odorous  matter  of  the  axillae  is  secreted  form  a  nearly 
complete  layer  under  the  cutis,  and  are  like  the  ordinary  su- 
doriparous glands,  except  in  being  larger  and  having  very 
short  ducts.  In  the  neck  and  back,  where  they  are  least 
numerous,  the  glands  amount  to  417  on  the  square  inch 
(Krause).  Their  total  number  Krause  estimates  at  2,381,248 ; 
and,  supposing  the  orifice  of  each  gland  to  present  a  surface 
of  s'gth  of  a  line  in  diameter  (and  regarding  a  line  as  equal 
to  T!flth  of  an  inch),  he  reckons  that  the  whole  of  the  glands 
would  present  an  evaporating  surface  of  about  eight  square 
inches.1 

Sebaceous  Glands. — Besides  the  perspiration,  the  skin  se- 
cretes a  peculiar  fatty  matter,  and  for  this  purpose  is  provided 
with  another  set  of  special  organs,  termed  sebaceous  glands 
(Fig.  115),  which,  like  the  sudoriparous  glands,  are  abun- 
dantly distributed  over  most  parts  of  the  body.  They  are 
most  numerous  in  parts  largely  supplied  with  hair,  as  the 
scalp  and  face,  and  are  thickly  distributed  about  the  entrances 
of  the  various  passages  into  the  body,  as  the  anus,  nose,  lips, 
and  external  ear.  They  are  entirely  absent  from  the  palmar 
surface  of  the  hands  and  the  plantar  surfaces  of  the  feet. 
They  are  minutely  lobulated  glands,  composed  of  an  aggregate 
of  small  vesicles  or  sacculi  filled  with  opaque  white  substances, 
like  soft  ointment.  Minute  capillary  vessels  overspread  them  ; 
and  their  ducts,  which  have  a  bearded  appearance,  as  if  formed 
of  rows  of  shells,  open  either  on  the  surface  of  the  skin,  close 
to  a  hair,  or,  which  is  more  usual,  directly  into  the  follicle  of 
the  hair.  In  the  latter  case,  there  are  generally  two  glands 
to  each  hair  (Fig.  115). 


1  The  peculiar  bitter  yellow  substance  secreted  by  the  skin  of  the 
external  auditory  passage  is  named  cerumen,  and  the  glands  them- 
selves ceruminous  glands  ;  but  they  do  not  much  differ  in  structure 
from  the  ordinary  sudoriparous  glands. 


340 


THE    SKIN. 


Structure  of  Hair  and  Nails. 

Hair. — A  hair  is  produced  by  a  peculiar  growth  and  modi- 
fication of  the  epidermis.     Externally  it  is  covered  by  a  layer 


FIG-  115a. 


FIG.  115. — Sebaceous  glands  of  the  skin,  after  Gurlt :  or,  a,  sebaceous  glands  opening 
into  the  follicle  of  the  hair  by  efferent  ducts ;  b,  a  hair  on  its  follicle. 

FIG.  11 5a.— Sweat-gland  and  the  commencement  of  its  duct.  a.  Venous  radicles 
on  the  wall  of  the  cell  in  which  the  gland  rests.  This  vein  anastomoses  with  others 
in  the  vicinity,  b.  Capillaries  of  the  gland  separately  represented,  arising  from 
their  arteries,  which  also  anastomose.  The  bloodvessels  are  all  situated  on  the  out- 
side or  deep  surface  of  the  tube,  in  contact  with  the  basement-membrane.— Magn. 
35  diam. 


of  fine  scales  closely  imbricated,  or  overlapping  like  the  tiles 
of  a  house,  but  with  the  free  edges  turned  upwards  (Fig.  116, 
A).  It  is  called  the  cuticle  of  the  hair.  Beneath  this  is  a 
much  thicker  layer  of  elongated  horny  cells,  closely  packed 
together  so  as  to  resemble  a  fibrous  structure.  This,  very 
commonly,  in  the  human  subject,  occupies  the  whole  of  the 
inside  of  the  hair ;  but  in  some  cases  there  is  left  a  small  cen- 
tral space  filled  by  a  substance  called  the  medulla  or  pith, 
composed  of  small  collections  of  irregularly  shaped  cells,  con- 
taining fat-  and  pigment-granules. 

The  follicle,  in  which  the  root  of  each  hair  is  contained 
(Fig.  117),  forms  a  tubular  depression  from  the  surface  of  the 


STRUCTURE    OF    HAIR.  341 

skin, — descending  into  the  subcutaneous  fat,  generally  to  a 
greater  depth  than  the  sudoriparous  glands,  and  at  its  deepest 
part  enlarging  in  a  bulbous  form,  and  often  curving  from  its 


FIG.  116. 


A,  surface  of  a  white  hair,  magnified  160  diameters.  The  wave  lines  mark  the 
upper  or  free  edges  of  the  cortical  scales.  £,  separated  scales,  magnified  350  diame- 
ters (after  Kolliker). 

previous  rectilinear  course.  It  is  lined  throughout  by  cells  of 
epithelium,  continuous  with  those  of  the  epidermis,  and  its 
walls  are  formed  of  pellucid  membrane,  which  commonly,  in 
the  follicles  of  the  largest  hairs,  has  the  structure  of  vascular 
fibro-cellular  tissue.  At  the  bottom  of  the  follicle  is  a  small 
papilla,  or  projection  of  true  skin,  and  it  is  by  the  production 
and  outgrowth  of  epidermal  cells  from  the  surface  of  this  pa- 
pilla that  the  hair  is  formed.  The  inner  wall  of  the  follicle  is 
lined  by  epidermal  cells  continuous  with  those  covering  the 
general  surface  of  the  skin ;  as  if  indeed  the  follicle  had  been 
formed  by  a  simple  thrusting  in  of  the  surface  of  the  integu- 
ment (Figs.  117,  118).  This  epidermal  lining  of  the  hair- 
follicle,  or  root-sheath  of  the  hair,  is  composed  of  two  layers, 
the  inner  one  of  which  is  so  moulded  on  the  imbricated  scaly 
cuticle  of  the  hair,  that  its  inner  surface  becomes  imbricated 
also,  but  of  course  in  the  opposite  direction.  When  a  hair  is 
pulled  out,  the  inner  layer  of  the  root-sheath  and  part  of  the 
outer  layer  also  are  commonly  pulled  out  with  it. 

Nails. — A  nail,  like  a  hair,  is  a  peculiar  arrangement  of 
epidermal  cells,  the  undermost  of  which,  like  those  of  the 
general  surface  of  the  integument,  are  rounded  or  elongated, 
while  the  superficial  are  flattened,  and  of  more  horny  consist- 
ence. That  specially  modified  portion  of  the  corium,  or  true 
skin,  by  which  the  nail  is  secreted,  is  called  the  matrix. 

The  back  edge  of  the  nail,  or  the  root  as  it  is  termed,  is 
received  into  a  shallow  crescentic  groove  in  the  matrix,  while 
the  front  part  is  free,  and  projects  beyond  the  extremity  of  the 
digit.  The  intermediate  portion  of  the  nail  rests  by  its  broad 

29 


342 


THE 


under  surface  on  the  front  part  of  the  matrix,  which  is  here 
called  the  bed  of  the  nail.     This  part  of  the  matrix  is  not  uni- 


FIG.  117. 


FIG.  118. 

a  be 


FIG.  117.— Medium-sized  hair  in  its  follicle,  magnified  50  diameters  (from  Kolli- 
ker).  a,  stem  cut  short ;  b,  root ;  c,  knob ;  d,  hair  cuticle  ;  e,  internal,  and/,  external 
root-sheath  ;  g,  h,  dermic  coat  of  follicle ;  i,  papilla  ;  k,  k,  ducts  of  sebaceous  glands ; 
I,  corium ;  m,  mucous  layer  of  epidermis ;  o,  upper  limit  of  internal  root-sheath  (from 
Kolliker). 

FIG.  118  — Magnified  view  of  the  root  of  a  hair  (after  Kohlrausch).  a,  stem  or 
shaft  of  hair  cut  across ;  6,  inner,  and  c,  outer  layer  of  the  epidermal  lining  of  the 
hair-follicle,  called  also  the  inner  and  outer  root-sheath  ;  d,  dermal  or  external  coat 
of  the  hair-follicle,  shown  in  part;  e,  imbricated  scales  about  to  form  a  cortical  layer 
on  the  surface  of  the  hair.  The  adjacent  cuticle  of  the  root-sheath  is  not  repre- 
sented, and  the  papilla  is  hidden  in  the  lower  part  of  the  knob  where  that  is  rep- 
resented lighter. 

formly  smooth  on  the  surface,  but  is  raised  in  the  form  of  lon- 
gitudinal and  nearly  parallel  ridges  or  laminae,  on  which  are 


STRUCTURE    OF     NAILS.  343 

moulded  the  epidermal  cells  of  which  the  nail  is  made  up 
(Fig.  119). 

The  growth  of  the  nail,  like  that  of  a  hair,  or  of  the  epi- 
dermis generally,  is  effected  by  a  constant  production  of  cells 
from  beneath  and  behind,  to  take  the  place  of  those  which  are 
worn  or  cut  away.  Inasmuch,  however,  as  the  posterior  edge 
of  the  nail,  from  its  being  lodged  in  a  groove  of  the  skin,  can- 
no.  119. 


Vertical  transverse  section  through  a  small  portion  of  the  nail  and  matrix  largely 

magnified  (after  Kolliker). 

A,  corium  of  the  nail-bed,  raised  into  ridges  or  laminie  a,  fitting  in  between  cor- 
responding laminae  ft,  of  the  nail.  B,  Malpighian,  and  C,  horny  layer  of  nail;  d, 
deepest  and  vertical  cells  ;  e,  upper  flattened  cells  of  Malpighian  layer. 

not  grow  backwards,  on  additions  being  made  to  it,  so  easily 
as  it  can  pass  in  the  opposite  direction,  any  growth  at  its 
hinder  part  pushes  the  whole  forwards.  At  the  same  time 
fresh  cells  are  added  to  its  under  surface,  and  thus  each  por- 
tion of  the  nail  becomes  gradually  thicker  as  it  moves  to  the 
front,  until,  projecting  beyond  the  surface  of  the  matrix,  it  can 
receive  no  fresh  addition  from  beneath,  and  is  simply  moved 
forwards  by  the  growth  at  its  root,  to  be  at  last  worn  away  or 
cut  off. 


344  THE    SKIN. 


Excretion  by  the  Skin. 

The  skin,  as  already  stated,  is  the  seat  of  a  twofold  excre- 
tioD  ;  of  that  formed  by  the  sebaceous  glands  and  hair-follicles, 
and  of  the  more  watery  fluid,  the  sweat  or  perspiration,  elimi- 
nated by  the  sudoriparous  glands. 

The  secretion  of  the  sebaceous  glands  and  hair-follicles  (for 
their  products  cannot  be  separated)  consists  of  cast-off  epithe- 
lium-cells, with  nuclei  and  granules,  together  with  an  oily 
matter,  extractive  matter,  and  stearin  ;  in  certain  parts,  also,  it 
is  mixed  with  a  peculiar  odorous  principle,  which  is  said  by 
Dr.  Fischer  to  contain  caproic,  butyric,  and  rutic  acids.  It  is, 
perhaps,  nearly  similar  in  composition  to  the  unctuous  coat- 
ing, or  vernix  caseosa,  which  is  formed  on  the  body  of  the 
foetus  while  in  the  uterus,  and  which  contains  large  quantities 
both  of  olein  and  margariu  ( J.  Davy).  Its  purpose  seems  to 
be  that  of  keeping  the  skin  moist  and  supple,  and,  by  its  oily 
nature,  of  both  hindering  the  evaporation  from  the  surface, 
and  guarding  the  skin  from  the  effects  of  the  long-continued  ac- 
tion of  moisture.  But  while  it  thus  serves  local  purposes,  its 
removal  from  the  body  entitles  it  to  be  reckoned  among  the 
excretions  of  the  skin ;  though  the  share  it  has  in  the  purify- 
ing of  the  blood  cannot  be  discerned. 

The  fluid  secreted  by  the  sudoriparous  glands  is  usually 
formed  so  gradually,  that  the  watery  portion  of  it  escapes  by 
evaporation  as  fast  as  it  reaches  the  surface.  But,  during 
strong  exercise,  exposure  to  great  external  warmth,  in  some 
diseases,  and  when  evaporation  is  prevented  by  the  application 
of  oiled  silk  or  plaster,  the  secretion  becomes  more  sensible 
and  collects  on  the  skin  in  the  form  of  drops  of  fluid.  A  good 
analysis  of  the  secretion  of  these  glands,  unmixed  with  other 
fluids  secreted  from  the  skin,  can  scarcely  be  made ;  for  the 
quantity  that  can  be  collected  pure  is  very  small.  Krause  in 
a  few  drops  from  the  palm  of  the  hand,  found  an  acid  reac- 
tion, oily  matter,  and  margarin,  with  water. 

The  perspiration  of  the  skin,  as  the  term  is  sometimes  em- 
ployed in  physiology,  includes  all  that  portion  of  the  secre- 
tions and  exudations  from  the  skin  which  passes  off  by  evap- 
oration ;  the  sweat  includes  that  which  may  be  collected  only 
in  drops  of  fluid  on  the  surface  of  the  skin.  The  two  terms 
are,  however,  most  often  used  synonymously ;  and  for  distinc- 
tion, the  former  is  called  insensible  perspiration :  the  latter, 
sensible  perspiration.  The  fluids  are  the  same,  except  that  the 
sweat  is  commonly  mingled  wTith  various  substances  lying  on 
the  surface  of  the  skin.  The  contents  of  the  sweat  are,  in  part, 
matters  capable  of  assuming  the  form  of  vapor,  such  as  car- 


THE    SWEAT.  345 

bonic  acid  and  water,  and  in  part,  other  matters  which  are 
deposited  on  the  skin,  and  mixed  with  the  sebaceous  secretion. 
Thenard  collected  the  perspiration  in  a  flannel  shirt  which  had 
been  washed  in  distilled  water,  and  found  in  it  chloride  of 
sodium,  acetic  acid,  some  phosphate  of  soda,  traces  of  phos- 
phate of  lime,  and  oxide  of  iron,  together  with  an  animal  sub- 
stance. In  sweat  which  had  run  from  the  forehead  in  drops, 
Berzelius  found  lactic  acid,  chloride  of  sodium,  and  chloride 
of  ammonium.  Anselmino  placed  his  arm  in  a  glass  cylinder, 
and  closed  the  opening  around  it  with  oiled  silk,  taking  care 
that  the  arm  touched  the  glass  at  no  point.  The  cutaneous 
exhalations  collected  on  the  interior  of  the  glass,  and  ran 
down  as  a  fluid :  on  analyzing  this,  he  found  water,  acetate  of 
ammonia,  and  carbonic  acid ;  and  in  the  ashes  of  the  dried 
residue  of  sweat  he  found  carbonate,  sulphate,  and  phosphate 
of  soda,  and  some  potash,  with  chloride  of  sodium,  phosphate 
and  carbonate  of  lime,  and  traces  of  oxide  of  iron.  Urea  has 
also  been  shown  to  be  an  ordinary  constituent  of  the  fluid  of 
perspiration. 

The  ordinary  constituents  of  perspiration,  may,  therefore, 
according  to  Gorup-Besanez,  be  thus  summed  up :  water,  fat, 
acetic,  butyric  and  formic  acid,  urea,  and  salts.  The  princi- 
pal salts  are  the  chlorides  of  sodium  and  potassium,  together 
with,  in  small  quantity,  alkaline  and  earthy  phosphates  and 
sulphates ;  and,  lastly,  some  oxide  of  iron.  Of  these  several 
substances,  none,  however,  need  particular  consideration,  ex- 
cept the  carbonic  acid  and  water. 

The  quantity  of  watery  vapor  excreted  from  the  skin  was 
estimated  very  carefully  by  Lavoisier  and  Sequin.  The  latter 
chemist  inclosed  his  body  in  an  air-tight  bag,  with  a  mouth- 
piece. The  bag  being  closed  by  a  strong  band  above,  and  the 
mouth-piece  adjusted  and  gummed  to  the  skin  around  the 
mouth,  he  was  weighed,  and  then  remained  quiet  for  several 
hours,  after  which  time  he  was  again  weighed.  The  differ- 
ence in  the  two  weights  indicated  the  amount  of  loss  by  pul- 
monary exhalation.  Having  taken  off  the  air-tight  dress,  he 
was  immediately  weighed  again,  and  a  fourth  time  after  a  cer- 
tain interval.  The  difference  between  the  two  weights  last 
ascertained  gave  the  amount  of  the  cutaneous  and  pulmonary 
exhalation  together ;  by  subtracting  from  this  the  loss  by  pul- 
monary exhalation  alone,  while  he  was  in  the  air-tight  dress, 
he  ascertained  the  amount  of  cutaneous  transpiration.  The 
repetition  of  these  experiments  during  a  long  period,  showed 
that,  during  a  state  of  rest,  the  average  loss  by  cutaneous  and 
pulmonary  exhalation  in  a  minute,  is  from  seventeen  to  eigh- 
teen grains, — the  minimum  eleven  grains,  the  maximum 


346  THE    SKIN. 

thirty-two  grains ;  and  that  of  the  eighteen  grains,  eleven  pass 
off  by  the  ski  a,  and  seven  by  the  lungs.  The  maximum  loss 
by  exhalation,  cutaneous  and  pulmonary,  in  twenty-four  hours, 
is  about  3f  lb.;  the  minimum  about  H  lb.  Valentin  found 
the  whole  quantity  lost  by  exhalation  from  the  cutaneous  and 
respiratory  surfaces  of  a  healthy  man  who  consumed  daily 
40,000  grains  of  food  and  drink,  to  be  19,000  grains  or  2f  lb. 
Subtracting  from  this,  for  the  pulmonary  exhalation,  5000 
grains,  and,  for  the  excess  of  the  weight  of  the  exhaled  car- 
bonic acid  over  that  of  the  equal  volume  of  the  inspired  oxy- 
gen, 2256  grains,  the  remainder,  11,744  grains,  or  nearly  if 
lb.,  may  represent  an  average  amount  of  cutaneous  exhalation 
in  the  day. 

The  large  quantity  of  watery  vapor  thus  exhaled  from  the 
skin,  will  prove  that  the  amount  excreted  by  simple  transuda- 
tion  through  the  cuticle  must  be  very  large,  if  we  may  take 
Krause's  estimate  of  about  eight  square  inches  for  the  total 
evaporating  surface  of  the  sudoriparous  glands ;  for  not  more 
than  about  3365  grains  could  be  evaporated  from  such  a  sur- 
face in  twenty-four  hours,  under  the  ordinary  circumstances  in 
which  the  surface  of  the  skin  is  placed.  This  estimate  is  not 
an  improbable  one,  for  it  agrees  very  closely  with  that  of 
Milne-Edwards,  who  calculated  that  when  the  temperature  of 
the  atmosphere  is  not  above  68°  F.,  the  glandular  secretion 
of  the  skin  contributes  only  Jth  to  the  total  sum  of  cutaneous 
exhalation. 

The  quantity  of  watery  vapor  lost  by  transpiration,  is  of 
course  influenced  by  all  external  circumstances  which  affect 
the  exhalation  irom  other  evaporating  surfaces,  such  as  the 
temperature,  the  hygrometric  state,  and  the  stillness  of  the 
atmosphere.  But,  of  the  variations  to  which  it  is  subject  un- 
der the  influence  of  these  conditions,  no  calculation  has  been 
exactly  made. 

Neither,  until  recently,  has  there  been  any  estimate  of  the 
quantity  of  carbonic  acid  exhaled  by  the  skin  on  an  average, 
or  in  various  circumstances.  Regnault  and  Reiset  attempted 
to  supply  this  defect,  and  concluded,  from  some  careful  exper- 
iments, that  the  quantity  of  carbonic  acid  exhaled  from  the 
skin  of  a  warm-blooded  animal  is  about  -^th  of  that  furnished 
by  the  pulmonary  respiration.  Dr.  Edward  Smith's  calcula- 
tion is  somewhat  less  than  this.  The  cutaneous  exhalation  is 
most  abundant  in  the  lower  classes  of  animals,  more  particu- 
larly the  naked  Amphibia,  as  frogs  and  toads,  whose  skin  is 
thin  and  moist,  and  readily  permits  an  interchange  of  gases 
between  the  blood  circulating  in  it  and  the  surrounding  atmos- 
phere. Bischoff  found  that,  after  the  lungs  of  frogs  had  been 


ABSORPTION    BY    THE    SKIN.  347 

tied  and  cut  out,  about  a  quarter  of  a  cubic  inch  of  carbonic 
acid  gas  was  exhaled  by  the  skin  in  eight  hours.  And  this 
quantity  is  very  large,  when  it  is  remembered  that  a  full-sized 
frog  will  generate  only  about  half  a  cubic  inch  of  carbonic 
acid  by  his  lungs  and  skin  together  in  six  hours  (Milne- 
Edwards  and  Miiller).  That  the  respiratory  function  of  the 
skin  is,  perhaps,  even  more  considerable  in  the  higher  animals 
than  appears  to  be  the  case  from  the  experiments  of  Regnault 
and  Reiset  just  alluded  to,  seemed  probable  by  the  fact  ob- 
served by  Magendie  and  others,  that  if  the  skin  of  animals  is 
covered  with  an  impermeable  varnish,  or  the  body  inclosed, 
all  but  the  head,  in  a  caoutchouc  dress,  animals  soon  die,  as  if 
asphyxiated  ;  their  heart  and  lungs  being  gorged  with  blood, 
and  their  temperatures,  during  life,  gradually  falling  many 
degrees,  and  sometimes  as  much  as  36°  F.  below  the  ordinary 
standard  (Magendie).  Some  recent  experiments  of  Lashke- 
witzch  appear,  however,  to  confirm  the  opinion  of  Valentin, 
that  loss  of  temperature  is  the  immediate  cause  of  death  in 
these  cases.  A  varnished  animal  is  said  to  have  suffered  no 
harm  when  surrounded  by  cotton  wadding,  but  it  died  when 
the  wadding  was  removed. 

Absorption  by  the  skin  has  been  already  mentioned,  as  an 
instance  in  which  that  process  is  most  actively  accomplished. 
Metallic  preparations  rubbed  into  the  skin  have  the  same 
action  as  when  given  internally,  only  in  a  less  degree.  Mer- 
cury applied  in  this  manner  exerts  its  specific  influence  upon 
syphilis,  and  excites  salivation  ;  potassio-tartrate  of  antimony 
may  excite  vomiting,  or  an  eruption  extending  over  the  whole 
body  ;  and  arsenic  may  produce  poisonous  effects.  Vegetable 
matters,  also,  if  soluble,  or  already  in  solution,  give  rise  to 
their  peculiar  effects,  as  cathartics,  narcotics,  and  the  like, 
when  rubbed  into  the  skin.  The  effect  of  rubbing  is  probably 
to  convey  the  particles  of  the  matter  into  the  orifices  of  the 
glands  whence  they  are  more  readily  absorbed  than  they 
would  be  through  the  epidermis.  When  simply  left  in  con- 
tact with  the  skin,  substances,  unless  in  a  fluid  state,  are  sel- 
dom absorbed. 

It  has  long  been  a  contested  question  whether  the  skin 
covered  with  the  epidermis  has  the  power  of  absorbing  water  ; 
and  it  is  a  point  the  more  difficult  to  determine  because  the 
skin  loses  water  by  evaporation.  But,  from  the  result  of 
many  experiments,  it  may  now  be  regarded  as  a  well-ascer- 
tained fact  that  such  absorption  really  occurs.  M.  Edwards 
has  proved  that  the  absorption  of  water  by  the  surface  of  the 
body  may  take  place  in  the  lower  animals  very  rapidly.  Not 
only  frogs,  which  have  a  thin  skin,  but  lizards,  in  which  the 


348  THE    SKIN. 

cuticle  is  thicker  than  in  man,  after  having  lust  weight  by 
being  kept  for  some  time  in  a  dry  atmosphere,  were  found  to 
recover  both  their  weight  and  plumpness  very  rapidily  when 
immersed  in  water.  When  merely  the  tail,  posterior  extremi- 
ties, and  posterior  part  of  the  body  of  the  lizard  were  im- 
mersed, the  water  absorbed  was  distributed  throughout  the 
system.  And  a  like  absorption  through  the  skin,  though  to  a 
less  extent,  may  take  place  also  in  man. 

Dr.  Madden,  having  ascertained  the  loss  of  weight,  by 
cutaneous  and  pulmonary  transpiration,  that  occurred  during 
half  an  hour  in  the  air,  entered  the  bath,  and  remained  im- 
mersed during  the  same  period  of  time  breathing  through  a 
tube  which  communicated  with  the  air  exterior  to  the  room. 
He  was  then  carefully  dried  and  again  weighed.  Twelve 
experiments  were  performed  in  this  manner ;  and  in  ten  there 
was  a  gain  of  weight,  varying  from  2  scruples  to  5  drachms 
and  4  scruples,  or  a  mean  gain  of  1  drachm  2  scruples  and  13 
grains.  The  loss  in  the  air  during  the  same  length  of  time 
(half  an  hour)  varied  in  ten  experiments  from  2J  drachms  to 
1  ounce  2J  scruples,  or  in  the  mean  was  about  6J  drachms. 
So  that,  admitting  the  supposition  that  the  cutaneous  trans- 
piration was  entirely  suspended,  and  estimating  the  loss  by 
pulmonary  exhalation  at  3  drachms,  there  was,  in  these  ten 
experiments  of  Dr.  Madden,  an  average  absorption  of  4 
drachms  1  scruple,  and  3  grains,  by  the  surface  of  the  body, 
during  half  an  hour.  In  four  experiments  performed  by  M. 
Berthold,  the  gain  in  weight  was  greater  than  in  those  of  Dr. 
Madden. 

In  severe  cases  of  dysphagia,  when  not  even  fluids  can  be 
taken  into  the  stomach,  immersion  in  a  bath  of  warm  water  or 
of  milk  and  water  may  assuage  the  thirst ;  and  it  has  been 
found  in  such  cases  that  the  weight  of  the  body  is  increased  by 
the  immersion.  Sailors  also,  when  destitute  of  fresh  water, 
find  their  urgent  thirst  allayed  by  soaking  their  clothes  in  salt 
water  and  wearing  them  in  that  state  ;  but  these  effects  may  be 
in  part  due  to  the  hindrance  to  the  evaporation  of  water  from 
the  skin. 

The  absorption,  also,  of  different  kinds  of  gas  by  the  skin  is 
proved  by  the  experiments  of  Abernethy,  Cruikshank,  Beddoes, 
and  others.  In  these  cases,  of  course,  the  absorbed  gases  com- 
bine with  the  fluids,  and  lose  the  gaseous  form.  Several  phys- 
iologists have  observed  an  absorption  of  nitrogen  by  the  skin. 
Beddoes  says,  that  he  saw  the  arm  of  a  negro  become  pale  for 
a  short  time  when  immersed  in  chlorine ;  and  Abernethy  ob- 
served that  when  he  held  his  hands  in  oxygen,  nitrogen,  car- 


STRUCTURE    OF    THE     KIDNEY.  349 

bonic  acid,  and  other  gases  contained  in  jars,  over  mercury, 
the  volume  of  the  gases  became  considerably  diminished. 

The  share  which  the  evaporation  from  the  skin  has  in  the 
maintenance  of  the  uniform  temperature  of  the  body,  and  the 
necessary  adaptation  thereto  of  the  production  of  heat,  have 
been  already  mentioned  (p.  195). 


CHAPTER  XV. 

THE    KIDNEYS    AND    THEIR   SECRETION. 

Structure  of  the  Kidney. 

THE  kidney  is  covered  on  the  outside  by  a  rather  tough 
fibrous  capsule,  which  is  slightly  attached  by  its  inner  surface 
to  the  proper  substance  of  the  organ  by  means  of  very  fine 
fibres  of  areolar  tissue  and  minute  bloodvessels.  From  the 
healthy  kidney,  therefore,  it  may  be  easily  torn  off  without 

FIG.  120. 


Plan  of  a  longitudinal  section  through  the  pelvis  and  substance  of  the  right  kid- 
ney, i/£;  a,  the  cortical  substance;  b,  b,  broad  part  of  the  pyramids  of  Malpighi;  c,  c, 
the  divisions  of  the  pelvis  named  calyces,  laid  open  ;  c',  one  of  these  unopened ;  d, 
summit  of  the  pyramids  or  papillae  projecting  into  calyces ;  e,  e,  section  of  the  narrow 
part  of  two  pyramids  near  the  calyces ;  p,  pelvis  or  enlarged  divisions  of  the  ureter 
within  the  kidney ;  u,  the  ureter  ;  s,  the  sinus  ;  h,  the  hilus. 

30 


350      THE    KIDNEYS    AND   THEIR   SECRETION. 

injury  to  the  subjacent  cortical  portion  of  the  organ.  At  the 
hilus  or  notch  of  the  kidney,  it  becomes  continuous  with  the 
external  coat  of  the  upper  and  dilated  part  of  the  ureter. 

On  making  a  section  lengthwise  through  the  kidney  (Fig. 
120)  the  main  part  of  its  substance  is  seen  to  be  composed  of 
two  chief  portions,  called  respectively  the  cortical  and  the 
medullary  portion,  the  latter  being  also  sometimes  called  the 
pyramidal  portion,  from  the  fact  of  its  being  composed  of  about 
a  dozen  conical  bundles  of  urine-tubes,  each  bundle  being  called 
a  pyramid.  The  upper  part  of  the  duct  of  the  organ,  or  the 
ureter,  is  dilated  into  what  is  called  the  pelvis  of  the  kidney ; 
and  this,  again,  after  separating  into  two  or  three  principal 
divisions,  is  finally  subdivided  into  still  smaller  portions,  vary- 
ing in  number  from  about  8  to  12,  or  even  more,  and  called 
calyces.  Each  of  these  little  calyces  or  cups,  again  receives  the 
pointed  extremity  or  papilla  of  a  pyramid.  Sometimes,  how- 
ever, more  than  one  papilla  is  received  by  a  calyx. 

The  kidney  is  a  gland  of  the  class  called  tubular,  and  both 
its  cortical  and  medullary  portions  are  composed  essentially  of 
secreting  tubes,  the  tubuli  uriniferi,  which  by  one  extremity, 
in  the  cortical  portion,  end  commonly  in  little  saccules  con- 
taining bloodvessels,  called  Malpighian  bodies,  and  by  the 
other  open  through  the  papillae  into  the  pelvis  of  the  kidney, 
and  thus  discharge  the  urine  which  flows  through  them. 

In  the  pyramids  they  are  chiefly  straight— dividing  and 
diverging  as  they  ascend  through  these  into  the  cortical  por- 
tion ;  while  in  the  latter  region  they  spread  out  more  irregu- 
larly, and  become  much  branched  and  convoluted. 

The  tubuli  uriniferi  (Fig.  121)  are  composed  of  a  nearly 
homogeneous  membrane,  lined  internally  by  spheroidal  epithe- 
lium, and  for  the  greater  part  of  their  extent  are  about  gj^  of 
an  inch  in  diameter,— becoming  somewhat  larger  than  this 
immediately  before  they  open  through  the  papillae.  On  trac- 
ing these  tubules  upwards  from  the  papillse,  they  are  found  to 
divide  dichotomously  as  they  ascend  through  the  pyramids, 
and  on  reaching  the  bases  of  the  latter,  they  begin  to  branch 
and  diverge  more  widely,  and  to  form  by  their  branches  and 
convolutions  the  essential  part  of  the  cortical  portion  of  the 
organ.  At  their  extremities  they  become  dilated  into  the 
Malpighian  capsules.  Until  recently,  it  was  believed  that  the 
straight  tubules  in  the  pyramids  branch  out  and  become  con- 
voluted immediately  on  reaching  the  bases  of  the  pyramids ; 
but  between  the  straight  tubes  in  the  pyramids  and  the  convo- 
luted tubes  in  the  cortical  portion,  there  has  been  shown  to  be 
a  system  of  tubules  of  smaller  diameter  than  either,  which 
form  intercommunications  between  the  two  varieties  formerly 


STRUCTURE    OF    THE    KIDNEY. 


351 


recognized.  These  intervening  tubules,  called  the  looped  tubes 
of  Henle,  arising  from  the  straight  tubes  in  some  part  of  their 
course,  or  being  continued  from  their  extremities  at  the  bases 
of  the  pyramids,  pass  down  loopwise  in  the  pyramids  for  a 


FIG.  122. 


FIG.  121. 


FIG.  121. — A.  Portion  of  a  secreting  canal  from  the  cortical  substance  of  the  kid- 
ney. B.  The  epithelium  or  gland-cells,  more  highly  magnified  (700  times). 

FIG.  122.— Diagram  of  the  looped  uriniferous  tubes  and  their  connection  with  the 
capsules  of  the  glomeruli  (from  Southey,  after  Ludwig).  In  the  lower  part  of  the 
figure  one  of  the  large  branching  tubes  is  shown  opening  on  a  papilla;  in  the  mid- 
dle part  two  of  the  looped  small  tubes  are  seen  descending  to  form  their  loops,  and 
reascending  in  the  medullary  substance ;  while  in  the  upper  or  cortical  part,  these 
tubes,  after  some  enlargement,  are  represented  as  becoming  convoluted  and  dilated 
in  the  capsules  of  glomeruli. 

longer  or  shorter  distance,  and  then,  again  turning  up,  end  in 
the  convoluted  tubes  whose  extremities  are  dilated  into  the 
Malpighian  capsules  before  referred  to  (Fig.  122).  On  a 
transverse  section  of  a  pyramid  (Fig.  123),  these  looped  tubes 


352      THE    KIDNEYS    AND    THEIR    SECRETION. 

are  seen  to  be  of  much  smaller  calibre  than  the  straight  ones, 
which  are  passing  down  to  open  through  the  papillse. 

The  Malpighian  bodies  are  found  only  in  the  cortical  part  of 
the  kidney.  On  a  section  of  the  organ,  some  of  them  are  just 
visible  to  the  naked  eye  as  minute  red  points  ;  others  are  too 
small  to  be  thus  seen.  Their  average  diameter  is  about  T^a  of 
an  inch.  Each  of  them  is  composed  of  the  dilated  extremity 
of  a  urinary  tube,  or  Malpighian  capsule,  inclosing  a  tuft  of 
bloodvessels. 

In  connection  with  these  little  bodies  the  general  distribu- 
tion of  bloodvessels  to  the  kidney  may  be  here  considered. 

The  renal  artery  divides  into  several  branches,  which,  pass- 
ing in  at  the  hilus  of  the  kidney,  and  covered  by  a  fine  sheath 
of  areolar  tissue  derived  from  the  capsule,  enter  the  substance 
of  the  organ  chiefly  in  the  intervals  between  the  papillse,  and 
penetrate  the  cortical  substance,  where  this  dips  down  between 
the  bases  of  the  pyramids.  Here  they  form  a  tolerably  dense 

FIG.  123. 


Transverse  section  of  a  renal  papilla  (from  Kolhker)  -y^-  a,  larger  tubes  or  papil- 
lary ducts ;  b,  smaller  tubes  of  Henle ;  c,  bloodvessels,  distinguished  by  their  natter 
epithelium  ,  d,  nuclei  of  the  stroma. 

plexus  of  an  arched  form,  and  from  this  are  given  off  smaller 
arteries  which  ultimately  supply  the  Malpighian  bodies. 

The  small  afferent  artery  (Fig.  124),  which  enters  the  Mal- 
pighian body  by  perforating  the  capsule,  breaks  up  in  the  in- 
terior into  a  dense  and  convoluted  and  looped  capillary  plexus, 
which  is  ultimately  gathered  up  again  into  a  single  small  effer- 


STRUCTURE    OF    THE     KIDNEY.  353 

ent  vessel,  comparable  to  a  minute  vein,  which  leaves  the 
Malpighian  capsule  just  by  the  point  at  which  the  afferent 
artery  enters  it.  On  leaving,  it  does  not  immediately  join 
other  small  veins  as  might  have  been  expected,  but  again 
breaking  up  into  a  network  of  capillary  vessels,  is  distributed 
on  the  exterior  of  the  tubule,  from  whose  dilated  end  it  had 
just  emerged.  After  this  second  breaking  up  it  is  finally  col- 
lected into  a  small  vein,  which,  by  union  with  others  like  it, 
helps  to  form  the  radicles  of  the  renal  vein. 

The  Malpighian  capsule  is  lined  by  a  layer  of  fine  squamous 
epithelial  cells ;  but  whether  the  small  glomerulus  or  tuft  of 
capillaries  in  the  interior  is  covered  by  a  similar  layer  is  un- 

FIG.  124.  FIG.  125. 


FIG.  124.— Plan  of  the  renal  circulation  in  man  and  the  Mammalia,  a,  terminal 
branch  of  the  artery,  giving  the  terminal  twig  1,  to  the  Malpighian  tuft  m,  from 
which  emerges  the  efferent  or  portal  vessel,  2.  Other  efferent  vessels,  2,  are  seen 
entering  the  plexus  of  capillaries,  surrounding  the  uriniferous  tube,  /.  From  the 
plexus,  the  emulgent  vein,  v,  springs. 

FIG.  125. — Semidiagrammatic  representation  of  a  Malpighian  body  in  its  relation 
to  the  uriniferous  tube  (from  Kolliker)  -y-.  a,  capsule  of  the  Malpighian  body;  d, 
epithelium  of  the  uriniferous  tube ;  e,  detached  epithelium  ;  /,  afferent  vessel ;  g, 
efferent  vessel ;  k,  convoluted  vessels  of  the  glomerulus. 

certain.  Kolliker  believes  that  such  a  covering,  although  ex- 
ceedingly thin,  is  present,  and  has  delineated  the  appearance 
in  the  accompanying  diagram  (Fig.  125). 

Besides  the  small  afferent  arteries  of  the  Malpighian  bodies, 
there  are,  of  course,  others  which  are  distributed  in  the  ordi- 
nary manner,  for  nutrition's  sake,  to  the  different  parts  of  the 
organ ;  and  in  the  pyramids,  between  the  tubes,  there  are  nu- 


354      THE     KIDNEYS    AND    THEIR    SECRETION. 

merous  straight  vessels,  the  vasa  recta,  supposed  by  some  ob- 
servers to  be  branches  of  vasa  efferentia  from  Malpighian 
bodies,  and  therefore  comparable  to  the  venous  plexus  around 
the  tubules  in  the  cortical  portion,  while  others  think  that  they 
arise  directly  from  small  branches  of  the  renal  arteries. 

Between  the  tubes,  vessels,  &c.,  which  make  up  the  main 
substance  of  the  kidney,  there  exists  in  small  quantity  a  fine 
matrix  of  areolar  tissue. 

The  nerves  of  the  kidney  are  derived  from  the  renal  plexus.1 

Secretion  of  Urine. 

The  separation  from  the  blood  of  the  solids  in  a  state  of  so- 
lution in  the  urine  is  probably  effected,  like  other  secretions, 
by  the  agency  of  the  gland-cells,  and  equally  in  all  parts  of 
the  urine-tubes.  The  urea  and  uric  acid,  and  perhaps  some 
of  the  other  constituents  existing  ready  formed  in  the  blood, 
may  need  only  separation,  that  is,  they  may  pass  from  the 
blood  to  the  urine  without  further  elaboration ;  but  this  is  not 
the  case  with  some  of  the  other  principles  of  the  urine,  such  as 
the  acid  phosphates  and  the  sulphates,  for  these  salts  do  not 
exist  as  such  in  the  blood,  and  must  be  formed  by  the  chemi- 
cal agency  of  the  cells. 

The  watery  part  of  the  urine  is  probably  in  part  separated 
by  the  same  structures  that  secrete  the  solids,  but  the  ingeni- 
ous suggestion  of  Mr.  Bowman  that  the  water  of  the  urine  is 
mainly  strained  off,  so  to  speak,  by  the  Malpighiau  bodies, 
from  the  blood  which  circulates  in  their  capillary  tufts,  is  ex- 
ceedingly probable ;  although  if,  as  Kolliker  and  others  main- 
tain, there  is  an  epithelial  covering  to  these  tufts  or  glomeruli, 
it  is  very  likely  that  the  solids  of  the  urine  may  be  in  part  se- 
creted here  also.  We  may,  therefore,  conclude  that  all  parts 
of  the  tubular  system  of  the  kidney  take  part  in  the  secretion 
of  the  urine  as  a  whole,  but  that  there  is  a  provision  also  in 
the  arrangement  of  the  vessels  in  the  Malpighiau  bodies  for  a 
more  simple  draining  off  of  water  from  the  blood  when  re- 
quired. 

The  large  size  of  the  renal  arteries  and  veins  permits  so 
rapid  a  transit  of  the  blood  through  the  kidneys,  that  the 
whole  of  the  blood  is  purified  by  them.  The  secretion  of  urine 
is  rapid  in  comparison  with  other  secretions,  and  as  each  por- 

1  For  a  more  detailed  account  of  the  structure  of  the  kidney  and  a 
summary  of  the  various  opinions  on  the  subject,  the  student  may  be 
referred  especially  to  Quain's  Anatomy,  7th  ed.,  and  to  a  paper  by 
Dr.  Reginald  Southey,  in  vol.  i  of  the  St.  Bartholomew's  Hospital 
Reports. 


PASSAGE    OF    URINE    INTO   THE    BLADDER.       355 

tion  is  secreted,  it  propels  that  which  is  already  in  the  tubes 
onwards  into  the  pelvis  of  the  kidney.  Thence  through  the 
ureter  the  urine  passes  into  the  bladder,  into  which  its  rate 
and  mode  of  entrance  has  been  watched  in  cases  of  ectopia 
vesicse,  i.  e.,  of  such  fissures  in  the  anterior  and  lower  part  of 
the  walls  of  the  abdomen,  and  of  the  front  wall  of  the  bladder, 
as  exposed  to  view  its  hinder  wall  together  with  the  orifices  of 
the  ureters.  Some  good  observations  on  such  cases  were  made 
by  Mr.  Erichsen.  The  urine  does  not  enter  the  bladder  at 
any  regular  rate,  nor  is  there  a  synchronism  in  its  movement 
through  the  two  ureters.  During  fasting,  two  or  three  drops 
enter  the  bladder  every  minute,  each  drop  as  it  enters  first 
raising  up  the  little  papilla  on  which,  in  these  cases,  the  ureter 
opens,  and  then  passing  slowly  through  its  orifice,  which  at 
once  again  closes  like  a  sphincter.  In  the  recumbent  posture, 
the  urine  collects  for  a  little  time  in  the  ureters,  then  flows 
gently,  and,  if  the  body  be  raised,  runs  from  them  in  a  stream 
till  they  are  empty.  Its  flow  is  increased  in  deep  inspiration, 
or  straining,  and  in  active  exercise,  and  in  fifteen  or  twenty 
minutes  after  a  meal. 

The  same  observations,  also,  showed  how  fast  some  substances 
pass  from  the  stomach  through  the  circulation,  and  through  the 
vessels  of  the  kidneys.  Ferrocyanide  of  potassium  so  passed 
on  one  occasion  in  a  minute :  vegetable  substances,  such  as 
rhubarb,  occupied  from  sixteen  to  thirty-five  minutes ;  neutral 
alkaline  salts  with  vegetable  acids,  which  were  generally  de- 
composed in  transitu,  made  the  urine  alkaline  in  from  twenty- 
eight  to  forty-seven  minutes.  But  the  times  of  passage  varied 
much ;  and  the  transit  was  always  slow  when  the  substances 
were  taken  during  digestion. 

The  urine  collecting  in  the  urinary  bladder  is  prevented 
from  regurgitation  into  the  ureters  by  the  mode  in  which  these 
pass  through  the  walls  of  the  bladder,  namely,  by  their  lying 
for  between  half  and  three-quarters  of  an  inch  between  the 
muscular  and  mucous  coats,  and  then  turning  rather  abruptly 
forwards,  and  opening  through  the  latter,  it  collects  till  the 
distension  of  the  bladder  is  felt  either  by  direct  sensation,  or, 
in  ordinary  cases,  by  a  transferred  sensation  at  and  near  the 
orifice  of  the  urethra.  Then,  the  effort  of  the  will  being  di- 
rected primarily  to  the  muscles  of  the  abdomen,  and  through 
them  (by  reason  of  its  tendency  to  act  with  them)  to  the  urinary 
bladder,  the  latter,  though  its  muscular  walls  are  really  com- 
posed of  involuntary  muscle,  contracts,  and  expels  the  urine. 
(See  also  p.  183.) 


356  THE    URINE. 


The  Urine :  its  General  Properties. 

Healthy  urine  is  a  clear  limpid  fluid,  of  a  pale  yellow  or 
amber  color,  with  a  peculiar  faint  aromatic  odor,  which  be- 
comes pungent  and  ammoniacal  when  decomposition  takes 
place.  The  urine,  though  usually  clear  and  transparent  at 
first,  often  becomes  as  it  cools  opaque  and  turbid  from  the  de- 
position of  part  of  its  constituents  previously  held  in  solution  ; 
and  this  may  be  consistent  with  health,  though  it  is  only  in 
disease  that,  in  the  temperature  of  98°  or  100°,  at  which  it  is 
voided,  the  urine  is  turbid  even  when  first  expelled.  Although 
ordinarily  of  pale  amber  color,  yet,  consistently  with  health, 
the  urine  may  be  nearly  colorless,  or  of  a  brownish  or  deep 
orange  tint,  and,  between  these  extremes,  it  may  present  every 
shade  of  color. 

When  secreted,  and  most  commonly  when  first  voided,  the 
urine  has  a  distinctly  acid  reaction  in  man  and  all  carnivorous 
animals,  and  it  thus  remains  till  it  is  neutralized  or  made  alka- 
line by  the  ammonia  developed  in  it  by  decomposition.  In 
most  herbivorous  animals,  on  the  contrary,  the  urine  is  alka- 
line and  turbid.  The  difference  depends,  not  on  any  peculi- 
arity in  the  mode  of  secretion,  but  on  the  differences  in  the 
food  on  which  the  two  classes  subsist:  for  when  carnivorous 
animals,  such  as  dogs,  are  restricted  to  a  vegetable  diet,  their 
urine  becomes  pale,  turbid,  and  alkaline,  like  that  of  an  her- 
bivorous animal,  but  resumes  its  former  acidity  on  the  return 
to  an  animal  diet;  while  the  urine  voided  by  herbivorous  ani- 
mals, e.  g.,  rabbits,  fed  for  some  time  exclusively  upon  animal 
substances,  presents  the  acid  reaction  and  other  qualities  of  the 
urine  of  Carnivora,  its  ordinary  alkalinity  being  restored  only 
on  the  substitution  of  a  vegetable  for  the  animal  diet  (Bernard). 
Human  urine  is  not  usually  rendered  alkaline  by  vegetable 
diet,  but  it  becomes  so  after  the  free  use  of  alkaline  medicines, 
or  of  the  alkaline  salts  with  carbonic  or  vegetable  acids ;  for 
these  latter  are  changed  into  alkaline  carbonates  previous  to 
elimination  by  the  kidneys.  Except  in  these  cases,  it  is  very 
rarely  alkaline,  unless  ammonia  has  been  developed  in  it  by 
decomposition  commencing  before  it  is  evacuated  from  the 
bladder. 

The  average  specific  gravity  of  the  human  urine  is  about 
1020.  Probably  no  other  animal  fluid  presents  so  many  va- 
rieties in  density  within  twenty-four  hours  as  the  urine  does  ; 
for  the  relative  quantity  of  water  and  of  solid  constituents  of 
which  it  is  composed  is  materially  influenced  by  the  condition 
and  occupation  of  the  body  during  the  time  at  which  it  is  se- 
creted, by  the  length  of  time  which  has  elapsed  since  the  last 


COMPOSITION    OF    URINE.  357 

meal,  and  by  several  other  accidental  circumstances.  The  ex- 
istence of  these  causes  of  difference  in  the  composition  of  the 
urine  has  led  to  the  secretion  being  described  under  the  three 
heads  of  urina  sanguinis,  urina  potus,  and  urina  cibi.  The 
first  of  these  names  signifies  the  urine,  or  that  part  of  it  which 
is  secreted  from  the  blood  at  times  in  which  neither  food  nor 
drink  has  been  recently  taken,  and  is  applied  especially  to  the 
urine  which  is  evacuated  in  the  morning  before  breakfast.  The 
urina  potus  indicates  the  urine  secreted  shortly  after  the  intro- 
duction of  any  considerable  quantity  of  fluid  into  the  body  ; 
and  the  urina  cibi  the  portions  secreted  during  the  period  im- 
mediately succeeding  a  meal  of  solid  food.  The  last  kind  con- 
tains a  larger  quantity  of  solid  matter  than  either  of  the 
others  ;  the  first  or  second,  being  largely  diluted  with  water, 
possesses  a  comparatively  low  specific  gravity.  Of  these  three 
kinds,  the  morning  urine  is  the  best  calculated  for  analysis, 
since  it  represents  the  simple  secretion  unmixed  with  the  ele- 
ments of  food  or  drink  ;  if  it  be  not  used,  the  whole  of  the 
urine  passed  during  a  period  of  twenty  -four  hours  should  be 
taken.  In  accordance  with  the  various  circumstances  above- 
mentioned,  the  specific  gravity  of  the  urine  may,  consistently 
with  health,  range  widely  on  both  sides  of  the  usual  average. 
The  average  healthy  range  may  be  stated  at  from  1015  in  the 
winter  to  1025  in  the  summer,  and  variations  of  diet  and  ex- 
ercise may  make  as  great  a  difference.  In  disease,  the  varia- 
tion may  be  greater  ;  sometimes  descending,  in  albumin  uria, 
to  1004,  and  frequently  ascending  in  diabetes,  when  the  urine 
is  loaded  with  sugar,  to  1050,  or  even  to  1060. 

The  whole  quantity  of  urine  secreted  in  twenty-four  hours  is 
subject  to  variation  according  to  the  amount  of  fluid  drunk, 
and  the  proportion  of  the  latter  passing  off  from  the  skin, 
lungs,  and  alimentary  canal.  It  is  because  the  secretion  of 
the  skin  is  more  active  in  summer  than  in  winter,  that  the 
quantity  of  urine  is  smaller,  and  its  specific  gravity  propor- 
tionately higher.  On  taking  the  mean  of  numerous  observa- 
tions by  several  experimenters,  Dr.  Parkes  found  that  the 
average  quantity  voided  in  twenty-four  hours  by  healthy 
male  adults  from  twenty  to  forty  years  of  age,  amounted  to 
fluid  ounces. 


Chemical  Composition  of  the  Urine. 

The  urine  consists  of  water,  holding  in  solution  certain  ani- 
mal and  saline  matters  as  its  ordinary  constituents,  and  occa- 
sionally various  matters  taken  into  the  stomach  as  food  — 
salts,  coloring  matter,  and  the  like.  The  quantities  of  the 
several  natural  and  constant  ingredients  of  the  urine  are 


358 


THE    URINE. 


stated  somewhat  differently  by  the  different  chemists  who  have 
analyzed  it  ;  but  many  of  the  differences  are  not  important, 
and  the  well-known  accuracy  of  the  several  chemists  renders 
it  almost  immaterial  which  of  the  analyses  is  adopted.     The 
analyses  by  A.  Becquerel  being  adopted  by  Dr.  Prout,  and 
by  Dr.  Golding  Bird,  will  be  here  employed.     (Table  I.) 

Table  II  has  been   compiled  from  the  observations  of  Dr. 
Parkes,  and  of  numerous  other  authors  quoted  in  his  admira- 
ble work  on  the  urine. 

TABLE  I. 

Average  quantity  of  each  constituent  of  the  Urine  in  1000  parts. 
Water,  ...........     967. 

Urea,      ...........       14/230 

Uric  acid,       ...........  468 

Coloring  matter,  |  inseparable  from  )       10  lr? 

Mucus,  and  animal  extractive  matter,   j        each  other,       J 

Sulphates,  {^ 

{Lime, 
Magnesia, 
Ammonia, 


J 


Salts, 


Hippurate  of  soda, 
Fluoride  of  potassium, 


8.13-3 


Silica,      ...........     traces. 


TABLE  II. 


1000.000 


Average  quantity  of  the  chief  constituents  of  the  Urine  excreted  in 

24  hours  by  healthy  male  adults. 
Water,         ........       52.      fluid  ounces. 

Urea,  .         .         .         .         .         .         .         .         .     512.4  grains. 

Uric  acid, 

Hippuric  acid,  uncertain, 

Sulphuric  acid,    . 

Phosphoric  acid,  . 

Chlorine, 

Chloride  of  Ammonium, 

Potash, 


Soda,    . 
Lime,  . 
Magnesia, 
Mucus, 


Extractives, 


Creatin, 
Creatinin, 
Pigment, 
Xanthin, 
[  Hypoxanthin, 
Resinous  matter, 
&c. 


.       52. 
.     512.4 
8.5 
probablv  10  to  15. 

31.11 
45. 
105.0 
35.25 
58. 
125. 
3.5 
3. 
7. 


154.0 


UREA. 


359 


From  these  proportions,  however,  most  of  the  constituents 
are,  even  in  health,  liable  to  variations.  Especially  the  water 
is  so.  Its  variations  in  different  seasons,  and  according  to  the 
quantity  of  drink  and  exercise,  have  already  been  mentioned. 
It  is  also  liable  to  be  influenced  by  the  condition  of  the  ner- 
vous system,  being  sometimes  greatly  increased  in  hysteria,  and 
some  other  nervous  affections ;  and  at  other  times  diminished. 
In  some  diseases  it  is  enormously  increased  ;  and  its  increase 
may  be  either  attended  with  an  augmented  quantity  of  solid 
matter,  as  in  ordinary  diabetes,  or  may  be  nearly  the  sole 
change,  as  in  the  affection  termed  diabetes  iusipidus.  In  other 
diseases,  e.  g.,  the  various  forms  of  albumiuuria,  the  quantity 
may  be  considerably  diminished.  A  febrile  condition  almost 
always  diminishes  the  quantity  of  water ;  and  a  like  diminu- 
tion is  caused  by  any  affection  which  draws  off  a  large  quantity 
of  fluid  from  the  body  through  any  other  channel  than  that 
of  the  kidneys,  e.  g.,  the  bowels  and  the  skin. 

Urea. — Urea  is  the  principal  solid  constituent  of  the  urine, 
forming  nearly  one-half  of  the  whole  quantity  of  solid  matter. 
It  is  also  the  most  important  ingredient,  since  it  is  the  chief 
substance  by  which  the  nitrogen  of  decomposed  tissue  and 
superfluous  food  is  excreted 
from  the  body.  For  its  re-  FlG-  126 

moval,  the  secretion  of  urine 
seems  especially  provided ;  and 
by  its  retention  in  the  blood 
the  most  pernicious  effects  are 
produced. 

Urea,  like   the  other  solid 
constituents  of  the  urine,  ex- 
ists in  a  state  of  solution.   But 
it  may  be  procured  in  the  solid 
state,  and  then  appears  in  the 
form  of  delicate  silvery  acicu- 
lar  crystals,  which   under  the 
microscope,   appear    as    four- 
sided  prisms  (Fig.  126).     It  18  Crystals  of  urea. 
obtained  in  this  state  by  evapo- 
rating urine  carefully  to  the  consistence  of  honey,  acting  on 
the  inspissated  mass  with  four  parts  of  alcohol,  then  evaporat- 
ing the  alcoholic  solution,  and  purifying  the  residue  by  repeated 
solution  in  water  or  alcohol,  and  finally  allowing  it  to  crystallize. 
It  readily  combines  with  an  acid,  like  a  weak  base ;  and  may 
thus  be  conveniently  procured  in  the  form  of  a  nitrate,  by  add- 
ing about  half  a  drachm  of  pure  nitric  acid  to  double  that  quan- 
tity of  urine  in  a  watch-glass.   The  crystals  of  nitrate  of  urea  are 


360  THE    URINE. 

formed  more  rapidly  if  the  urine  have  been  previously  concen- 
trated by  evaporation. 

Urea  is  colorless  when  pure ;  when  impure,  yellow  or  brown  ; 
without  smell,  and  of  a  cooling,  nitre-like  taste ;  has  neither  an 
acid  nor  an  alkaline  reaction,  and  deliquesces  in  a  moist  and 
warm  atmosphere.  At  59°  F.  it  requires  for  its  solution  less 
than  its  weight  of  water ;  it  is  dissolved  in  all  proportions  by 
boiling  water ;  but  it  requires  five  times  its  weight  of  cold 
alcohol  for  its  solution.  At  248°  F.  it  melts  without  under- 
going decomposition  ;  at  a  still  higher  temperature  ebullition 
takes  place,  and  carbonate  of  ammonia  sublimes ;  the  melting 
mass  gradually  acquires  a  pulpy  consistence ;  and,  if  the  heat 
is  carefully  regulated,  leaves  a  gray-white  powder,  cyanic  acid. 

Urea  is  identical  in  composition  with  cyanate  of  ammonia, 
and  was  first  artificially  produced  by  Wohler  from  this  sub- 
stance. Thus : 

Cyanate  of  Ammonia.  Urea. 

CHNO.  H3N         =         CH4N20. 

The  action  of  heat  upon  urea  in  evolving  carbonate  of  am- 
monia, and  leaving  cyanic  acid,  is  thus  explained.  A  similar 
decomposition  of  the  urea  with  development  of  carbonate  of 
ammonia  ensues  spontaneously  when  urine  is  kept  for  some 
days  after  being  voided,  and  explains  the  ammoniacal  odor 
then  evolved.  It  is  probable  that  this  spontaneous  decom- 
position is  accelerated  by  the  mucus  and  other  animal  matters 
in  the  urine,  which,  by  becoming  putrid,  act  the  part  of  a 
ferment  and  excite  a  change  of  composition  in  the  surrounding 
compounds.  It  is  chiefly  thus  that  the  urea  is  sometimes  de- 
composed before  it  leaves  the  bladder,  when  the  mucous  mem- 
brane is  diseased,  and  the  mucus  secreted  by  it  is  both  more 
abundant  and,  probably,  more  prone  than  usual  to  become 
putrid.  The  same  occurs  also  in  some  affections  of  the  nervous 
system,  particularly  in  paraplegia. 

The  quantity  of  urea  excreted  is,  like  that  of  the  urine  itself, 
subject  to  considerable  variation.  It  is  materially  influenced 
by  diet,  being  greater  when  animal  food  is  exclusively  used, 
less  when  the  diet  is  mixed,  and  least  of  all  with  a  vegetable 
diet.  As  a  rule,  men  excrete  a  larger  quantity  than  women, 
and  persons  in  the  middle  periods  of  life  a  larger  quantity  than 
infants  or  old  people  (Lecanu).  The  quantity  of  urea  does  not 
necessarily  increase  and  decrease  with  that  of  the  urine,  though 
on  the  whole  it  would  seem  that  whenever  the  amount  of  urine 
is  much  augmented,  the  quantity  of  urea  also  is  usually  in- 
creased (Becquerel) ;  and  it  appears  from  observations  of  Genth, 
that  the  quantity  of  urea,  as  of  urine,  may  be  especially  in- 


UREA.  361 

creased  by  drinking  large  quantities  of  water.  In  various  dis- 
eases, as  albuminuria,  the  quantity  is  reduced  considerably  be- 
low the  healthy  standard,  while  in  other  affections  it  is  above  it. 

The  urea  appears  to  be  derived  from  two  different  sources. 
That  it  is  derived  in  part  from  the  uuassimilated  elements  of 
nitrogenous  food,  circulating  with  the  blood,  is  shown  in  the 
increase  which  ensues  on  substituting  an  animal  or  highly 
nitrogenous  for  a  vegetable  diet ;  in  the  much  larger  amount, 
nearly  double,  excreted  by  Carnivora  than  Herbivora,  inde- 
pendent of  exercise ;  and  in  its  diminution  to  about  one-half 
during  starvation,  or  during  the  exclusion  of  non-nitrogenous 
principles  of  food.  But  that  it  is  in  larger  part  derived  from 
the  disintegration  of  the  azotized  animal  tissues,  is  shown  by 
the  fact  that  it  continues  to  be  excreted,  though  in  smaller 
quantity  than  usual,  when  all  nitrogenous  substances  are 
strictly  excluded  from  the  food,  as  when  the  diet  consists  for 
several  days  of  sugar,  starch,  gum,  oil,  and  similar  non-azotized 
vegetable  substances  (Lehmann).  It  is  excreted,  also,  even 
though  no  food  at  all  be  taken  for  a  considerable  time ;  thus 
it  is  found  in  the  urine  of  reptiles  which  have  fasted  for 
months ;  and  in  the  urine  of  a  madman,  who  had  fasted  eigh- 
teen days,  Lassaigne  found  both  urea  and  all  the  components 
of  healthy  urine.  Probably  all  the  nitrogenous  tissues  furnish 
a  share  of  urea  by  their  decomposition. 

It  has  been  commonly  taken  for  granted  that  the  quantity 
of  urea  in  the  urine  is  greatly  increased  by  active  exercise ;  but 
numerous  observers  have  failed  to  detect  more  than  a  slight 
increase  under  such  circumstances ;  and  our  notions  concern- 
ing the  relation  of  this  excretory  product  to  the  destruction  of 
muscular  fibre,  consequent  on  the  exercise  of  the  latter,  have 
lately  undergone  considerable  modification.  There  is  no 
doubt,  of  course,  that  like  all  parts  of  the  body,  the  muscles 
have  but  a  limited  term  of  existence,  and  are  being  constantly 
renewed,  at  the  same  time  that  a  part  of  the  products  of  their 
disintegration  appears  in  the  urine  in  the  form  of  urea.  But 
the  waste  is  not  so  fast  as  it  has  been  frequently  supposed  to 
be ;  and  the  theory  that  the  amount  of  wrork  done  by  the  muscle 
is  expressed  by  the  quantity  of  urea  excreted  in  the  urine,  and 
that  each  act  of  contraction  corresponds  to  an  equivalent  waste 
of  muscle-structure,  is  founded  on  error.  (See  also  chapter  on 
Motion.) 

Urea  exists  ready-formed  in  the  blood,  and  is  simply  ab- 
stracted therefrom  by  the  kidneys.  It  may  be  detected  in 
small  quantity  in  the  blood,  and  in  some  other  parts  of  the 
body,  e.  g.,  the  humors  of  the  eye  (Millon),  even  while  the  func- 
tions of  the  kidneys  are  unimpaired  :  but  when  from  any  cause, 


362  THE    URINE. 

especially  extensive  disease  or  extirpation  of  the  kidneys,  the 
separation  of  urine  is  imperfect,  the  urea  is  found  largely  in 
the  blood  and  in  most  other  fluids  of  the  body. 

Uric  Add. — This,  which  is  another  nitrogenous  animal  sub- 
stance, with  the  formula  C5N4 
FlG- 127-  H4O3,  and  was  formerly  termed 

lithic  acid,  on  account  of  its 
existence  in  many  forms  of 
urinary  calculi,  is  rarely  ab- 
sent from  the  urine  of  man  or 
animals,  though  in  the  feline 
tribe  it  seems  to  be  sometimes 
entirely  replaced  by  urea  (G. 
Bird).  Its  proportionate  quan- 
tity varies  considerably  in  dif- 
ferent animals.  In  man,  and 
Mammalia  generally,  especially 
the  Herbivora,  it  is  compara- 
tively small.  In  the  whole 

Various  forms  of  uric  acid  crystals.          ,    .1  /?  •>•    -i  i      (• 

tribe  oi  birds  and  01  serpents. 

on  the  other  hand,  the  quantity  is  very  large,  greatly  exceed- 
ing that  of  the  urea.  In  the  urine  of  granivorous  birds,  in- 
deed, urea  is  rarely  if  ever  found,  its  place  being  entirely  sup- 
plied by  uric  acid.  The  quantity  of  uric  acid,  like  that  of 
urea,  in  human  urine,  is  increased  by  the  use  of  animal  food, 
and  decreased  by  the  use  of  food  free  from  nitrogen,  or  by  an 
exclusively  vegetable  diet.  In  most  febrile  diseases,  and  in 
plethora,  it  is  formed  in  unnaturally  large  quantities  ;  and  in 
gout  it  is  deposited  in,  and  in  the  tissues  around,  joints,  in  the 
form  of  urate  of  soda,  of  which  the  so-called  chalkstones  of 
this  disease  are  principally  composed. 

The  condition  in  which  uric  acid  exists  in  solution  in  the 
urine  has  formed  the  subject  of  some  discussion,  because  of  its 
difficult  solubility  in  water. 

According  to  Liebig  the  uric  acid  exists  as  urate  of  soda, 
produced,  he  supposes,  by  the  uric  acid,  as  soon  as  it  is  formed, 
combining  with  part  of  the  base  of  the  alkaline  phosphate  of 
soda  of  the  blood.  Hippuric  acid,  which  exists  in  human 
urine  also,  he  believes,  acts  upon  the  alkaline  phosphate  in 
the  same  way,  and  increases  still  more  the  quantity  of  acid 
phosphate,  on  the  presence  of  which  it  is  probable  that  a  part 
of  the  natural  acidity  of  the  urine  depends.  It  is  scarcely 
possible  to  say  whether  the  union  of  uric  acid  with  the  base 
soda  and  probably  ammonia,  takes  place  in  the  blood,  or  in 
the  act  of  secretion  in  the  kidney ;  the  latter  is  the  more 
probable  opinion ;  but  the  quantity  of  either  uric  acid  or 


HIPPURIC    ACID. 


363 


urates  in  the  blood  is  probably  too  small  to  allow  of  this  ques- 
tion being  solved. 

The  source  of  uric  acid  is  probably  in  the  disintegrated  ele- 
ments of  albuminous  tissues.  The  relation  which  uric  acid 
and  urea  bear  to  each  other  is,  however,  still  obscure.  The 
fact  that  they  often  exist  together  in  the  same  urine,  makes  it 
seem  probable  that  they  have  different  origins  or  different 
offices  to  perform ;  but  the  entire  replacement  of  either  by  the 
other,  as  of  urea  by  uric  acid  in  the  urine  of  birds,  serpents, 
and  many  insects,  and  of  uric  acid  by  urea,  in  the  urine  of  the 
feline  tribe  of  Mammalia,  shows  that  each  alone  may  dis- 
charge all  the  important  functions  of  the  two. 

Owing  to  its  existence  in  combination  in  healthy  urine,  uric 
acid  for  examination  must  generally  be  precipitated  from  its 
bases  by  a  stronger  acid.  Frequently,  however,  when  ex- 
creted in  excess,  it  is  deposited  in  a  crystalline  form  (Fig.  127), 
mixed  with  large  quantities  of  urate  of  ammonia  or  soda  (Fig. 
130).  In  such  cases  it  may  be  procured  for  microscopic  exam- 
ination, by  gently  warming  the  portion  of  urine  containing  the 
sediment ;  this  dissolves  urate  of  ammonia  and  soda,  while  the 
comparatively  insoluble  crystals  of  uric  acid  subside  to  the 
bottom. 

The  most  common  form  in  which  uric  acid  is  deposited  in 
urine,  is  that  of  a  brownish  or  yellowish  powdery  substance, 
consisting  of  granules  of  urate  of  ammonia  or  soda.  When 
deposited  in  crystals,  it  is  most  frequently  in  rhombic  or  dia- 
mond-shaped laminae,  but  other  forms  are  not  uncommon  (Fig. 
127).  When  deposited  from  urine,  the  crystals  are  generally 
more  or  less  deeply  colored,  by  being  combined  with  the  color- 
ing principles  of  the  urine. 

Hippuric  Add  has  long  been  known  to  exist  in  the  urine  of 
herbivorous  animals  in  combi- 
nation with  soda.  Liebig  has 
shown  that  it  also  exists  nat- 
urally in  the  urine  of  man, 
in  quantity  equal  to  the  uric 
acid,  and  Weismann's  obser- 
vations agree  with  this.  It  is 
a  nitrogenous  compound  with 
the  formula  CgHgNOg.  It  is 
closely  allied  to  ben  zoic  acid  ; 
and  this  substance  when  in- 
troduced into  the  system,  is 
excreted  by  the  kidneys  as 
hippuric  acid  (Ure).  *  Its 
source  is  not  satisfactorily  de-  Crystals  of  hippuric  acid. 


364 


THE     URINE. 


FIG.  129. 


termined :  in  part  it  is  probably  derived  from  some  constitu- 
ents of  vegetable  diet,  though  man  has  no  hippuric  acid  in  his 
food,  nor,  commonly,  any  benzoic  acid  that  might  be  converted 
into  it ;  in  part  from  the  natural  disintegration  of  tissues,  inde- 
pendent of  vegetable  food,  for  Weismann  constantly  found  an 
appreciable  quantity,  even  when  living  on  an  exclusively  ani- 
mal diet. 

The  nature  and  composition  of  the  coloring  matter  of  urine 
are  involved  in  some  obscurity.  It  is  probably  closely  related 
to  the  coloring  matter  of  the  blood. 

The  mucus  in  the  urine  consists  principally  of  the  epithelial 
debris  of  the  mucous  surface  of  the  urinary  passages.  Particles 

of  epithelium,  in  greater  or  less 
abundance,  may  be  detected  in 
most  samples  of  urine,  especi- 
ally if  it  has  remained  at  rest 
for  some  time,  and  the  lower 
strata  are  then  examined  (Fig. 
129).  As  urine  cools,  the  mu- 
cus is  sometimes  seen  suspended 
in  it  as  a  delicate  opaque  cloud, 
but  generally  it  falls.  In  in- 
flammatory affections  of  the 
urinary  passages,  especially  of 
the  bladder,  mucus  in  large 
quantities  is  poured  forth,  and 
speedily  undergoes  decomposi- 
tion. The  presence  of  the  de- 
composing mucus  excites  (as  already  stated)  chemical  changes 
in  the  urea,  whereby  ammonia,  or  carbonate  of  ammonia,  is 
formed,  which,  combining  with  the  excess  of  acid  in  the  super- 
phosphates in  the  urine,  produces  insoluble  neutral  or  alkaline 
phosphates  of  lime  and  magnesia,  and  phosphate  of  ammonia 
and  magnesia.  These,  mixing  with  the  mucus,  constitute  the 
peculiar  white,  viscid,  mortar-like  substance  which  collects  upon 
the  mucous  surface  of  the  bladder,  and  is  often  passed  with  the 
urine,  forming  a  thick,  tenacious  sediment. 

Besides  mucus  and  coloring  matter,  urine  contains  a  consid- 
erable quantity  of  animal  matter,  usually  described  under  the 
obscure  name  of  animal  extractive.  The  investigations  of  Lie- 
big,  Heintz,  and  others,  have  shown  that  some  of  this  ill-defined 
substance  consists  of  Creatin  and  Creatinin,  two  crystallizable 
substances  derived,  probably,  from  the  metamorphosis  of  mus- 
cular tissue.  These  substances  appear  to  be  intermediate  be- 
tween the  proper  elements  of  the  muscles,  and,  perhaps,  of 
other  azotized  tissues  and  urea :.  the  first  products  of  the  dis- 


Mucus  deposited  from  urine. 


ALKALINE    AND    EARTHY    PHOSPHATES.       365 

integrating  tissues  probably  consisting  not  of  urea,  but  of  cre- 
atin  and  creatinin,  which  subsequently  are  partly  resolved  into 
urea,  partly  discharged,  without  change,  in  the  urine.  The 
names  of  some  other  substances  of  which  there  are  commonly 
traces  in  the  urine,  will  be  found  in  Table  II,  p.  358.  It  has 
been  shown  by  Scherer  that  much  of  the  substance  classed  as 
extractive  matter  of  the  urine,  is  the  peculiar  coloring  matter, 
probably  derived  from  the  haemoglobin  of  the  blood. 

Saline  Matter. — The  sulphuric  acid  in  the  urine  is  combined 
chiefly  or  entirely  with  soda  and  potash :  forming  salts  which 
are  taken  in  very  small  quantity  with  the  food,  and  are  scarcely 
found  in  other  fluids  or  tissues  of  the  body;  for  the  sulphates 
commonly  enumerated  among  the  constituents  of  the  ashes  of 
the  tissues  and  fluids  are,  for  the  most  part  or  entirely,  pro- 
duced by  the  changes  that  take  place  in  the  burning.  Dr. 
Parkes,  indeed,  considers  that  only  about  one-third  of  the  sul- 
phuric acid  found  in  the  urine  is  derived  directly  from  the 
food.  Hence  the  greater  part  of  the  sulphuric  acid  which  the 
sulphates  in  the  urine  contain,  must  be  formed  in  the  blood,  or 
in  the  act  of  secretion  of  urine;  the  sulphur  of  which  the  acid 
is  formed,  being  probably  derived  from  the  decomposing  nitro- 
genous tissues,  the  other  elements  of  which  are  resolved  into 
urea  and  uric  acid.  It  may  be  in  part  derived  also,  as  Dr. 
Parkes  observes,  from  the  sulphur-holding  taurin  and  cystin 
which  can  be  found  in  the  liver,  lungs,  and  other  parts  of  the 
body,  but  not  generally  in  the  excretions ;  and  which,  therefore, 
must  be  broken  up.  The  oxygen  is  supplied  through  the  lungs, 
and  the  heat  generated  during  combination  with  the  sulphur, 
is  one  of  the  subordinate  means  by  which  the  animal  tempera- 
ture is  maintained. 

Besides  the  sulphur  in  these  salts,  some  also  appears  to  be 
in  the  urine,  uncombined  with  oxygen ;  for  after  all  the  sul- 
phates have  been  removed  from  urine,  sulphuric  acid  may  be 
formed  by  drying  and  burning  it  with  nitre.  Mr.  Ronalds 
believes  that  from  three  to  five  grains  of  sulphur  are  thus 
daily  excreted.  The  combination  in  which  it  exists  is  certain  : 
possibly  it  is  in  some  compound  analogous  to  cystin  or  cystic 
oxide  (p.  367). 

The  phosphoric  acid  in  the  urine  is  combined  partly  with 
the  alkalies,  partly  with  the  alkaline  earths — about  four  or 
five  times  as  much  with  the  former  as  with  the  latter.  In 
blood,  saliva,  and  other  alkaline  fluids  of  the  body,  phosphates 
exist  in  the  form  of  alkaline  or  neutral  acid  salts.  In  the 
urine  they  are  acid  salts,  viz.,  the  phosphates  of  sodium,  am- 
monium, calcium,  and  magnesium,  the  excess  of  acid  being, 
according  to  Liebig,  due  to  the  appropriation  of  the  alkali 

31 


366 


THE     URINE. 


with  which  the  phosphoric  acid  in  the  blood  is  combined,  by 
the  several  new  acids  which  are  formed  or  discharged  at  the 
kidneys,  namely,  the  uric,  hippuric,  and  sulphuric  acids,  all  of 
which  he  supposes  to  be  neutralized  with  soda. 

The  presence  of  the  acid  phosphates  accounts,  in  great 
measure,  or,  according  to  Liebig,  entirely,  for  the  acidity  of 
the  urine.  The  phosphates  are  taken  largely  in  both  vege- 
table and  animal  food ;  some  thus  taken,  are  excreted  at  once  ; 
others,  after  being  transformed  and  incorporated  with  the  tis- 
sues. Phosphate  of  calcium  forms  the  principal  earthy  con- 
stituent of  bone,  and  from  the  decomposition  of  the  osseous 
tissue  the  urine  derives  a  large  quantity  of  this  salt.  The  de- 
composition of  other  tissues  also,  but  especially  of  the  brain 
and  nerve-substance,  furnishes  large  supplies  of  phosphorus  to 
the  urine,  which  phosphorus  is  supposed,  like  the  sulphur,  to 
be  united  with  oxygen,  and  then  combined  with  bases.  This 

quantity  is,  however,  liable  to 
FIG.  130.  considerable  variation.     Any 

undue  exercise  of  the  mind, 
and  all  circumstances  produc- 
ing nervous  exhaustion,  in- 
crease it.  The  earthy  phos- 
phates are  more  abundant  af- 
ter meals,  whether  on  animal 
or  vegetable  food,  and  are 
diminished  after  long  fasting. 
The  alkaline  phosphates  are 
increased  after  animal  food, 
diminished  after  vegetable 
food.  Exercise  increases  the 
alkaline,  but  not  the  earthy 
phosphates  (Bence  Jones). 
Phosphorus  uncombined  with 
oxygen  appears,  like  sulphur, 
to  be  excreted  in  the  urine 
(Ronalds).  When  the  urine  undergoes  alkaline  fermentation, 
phosphates  are  deposited  in  the  form  of  a  urinary  sediment 
consisting  chiefly  of  phosphate  of  ammonia  and  magnesia 
(triple  phosphate)  (Fig.  130.)  This  compound  does  not,  as 
such,  exist  in  healthy  urine.  The  ammonia  is  chiefly  or 
wholly  derived  from  the  decomposition  of  urea  (p.  360). 

The  chlorine  of  the  urine  occurs  chiefly  in  combination 
with  sodium,  but  slightly  also  with  ammonium,  and,  perhaps, 
potassium.  As  the  chlorides  exist  largely  in  food,  and  in  most 
of  the  animal  fluids,  their  occurrence  in  the  urine  is  easily 
understood. 


Urinary  sediment  of  triple  phosphates 
(large  prismatic  crystals)  and  urate  of 
ammonia,  from  urine  which  had  under- 
gone alkaline  fermentation. 


THE    NERVOUS    SYSTEM. 


367 


Cystin  (Fig.  132)  is  an  occasional  constituent  of  urine.  It 
resembles  taurin  in  containing  a  large  quantity  of  sulphur- 
more  than  25  per  cent.  It  does  not  exist  in  healthy  urine. 

Another  common  morbid  qonstituent  of  the  urine  is  oxalic 
acid,  which  is  frequently  deposited  in  combination  with  lime 


FIG.  181. 


FIG.  132. 


Crystals  of  oxalate  of  lime. 


Crystals  of  cystin. 


(Fig.  131)  as  a  urinary  sediment.     Like  cystin,  but  much 
more  commonly,  it  is  the  chief  constituent  of  certain  calculi. 
A  small  quantity  of  gas  is  naturally  present  in  the  urine 
in  a  state  of  solution.     It  consists  chiefly  of  carbonic  acid  and 
nitrogen. 


CHAPTER  XVI. 


THE   NERVOUS   SYSTEM. 

THE  nervous  system  consists  of  two  portions  or  systems,  the 
cerebro-spinal  and  the  sympathetic  or  ganglionic,  each  of  which 
(though  they  have  many  things  in  common)  possesses  certain 
peculiarities  in  structure,  mode  of  action,  and  range  of  influ- 
ence. 

The  cerebro-spinal  system  includes  the  brain  and  spinal 
cord,  with  the  nerves  proceeding  from  them,  and  the  several 
ganglia  seated  upon  these  nerves,  or  forming  part  of  the  sub- 
stance of  the  brain.  It  was  denominated  by  Bichat  the  ner- 
vous system  of  animal  life;  and  includes  all  the  nervous  organs 
in  and  through  which  are  performed  the  several  functions 


368  THE    NERVOUS    SYSTEM. 

with  which  the  mind  is  more  immediately  connected,  namely, 
those  relating  to  sensation  and  volition,  and  the  mental  acts 
connected  with  sensible  things. 

The  sympathetic  or  ganglionic  portion  of  the  nervous  system, 
which  Bichat  named  the  nervous  system  of  organic1  life,  con- 
sists essentially  of  a  chain  of  ganglia  connected  by  nervous 
cords,  which  extend  from  the  cranium  to  the  pelvis,  along 
each  side  of  the  vertebral  column,  and  from  which,  nerves 
with  ganglia  proceed  to  the  viscera  in  the  thoracic,  abdomi- 
nal, and  pelvic  cavities.  By  its  distribution,  as  well  as  by  its 
peculiar  mode  of  action,  this  system  is  less  immediately  con- 
nected with  the  mind,  either  as  conducting  sensations  or  the 
impulses  of  the  will ;  it  is  more  closely  connected  than  the 
cerebro-spinal  system  is  with  the  processes  of  organic  life. 

The  differences  however,  between  these  two  systems,  are  not 
essential :  their  actions  differ  in  degree  and  object  more  than 
in  kind  or  mode. 

Elementary  Structures  of  the  Nervous  System. 

The  organs  of  the  nervous  system  or  systems  are  composed 
essentially  of  two  kinds  of  structure,  vesicular  and  fibrous ; 
both  of  which  appear  esssential  to  the  construction  of  even  the 
simplest  nervous  system.  The  vesicular  structure  is  usually 
collected  in  masses,  and  mingled  with  the  fibrous  structure,  as 
in  the  brain,  spinal  cord,  and  the  several  ganglia ;  and  these 
masses  constitute  what  are  termed  nerve-centres,  being  the 
organs  in  which  it  is  supposed  that  nervous  force  may  be  gen- 
erated, and  in  which  are  accomplished  all  the  various  reflec- 
tions and  other  modes  of  disposing  of  impressions  when  they  are 
not  simply  conducted  along  nerve-fibres.  The  fibrous  nerve- 
substance,  besides  entering  into  the  composition  of  the  nervous 
centres,  forms  alone  the  nerves,  or  cords  of  communication, 
which  connect  the  various  nervous  centres,  and  are  distributed 
in  the  several  parts  of  the  body,  for  the  purpose  of  conveying 
nervous  force  to  them,  or  of  transmitting  to  the  nervous  cen- 
tres the  impressions  made  by  stimuli. 

1  The  term  organic  is  often  used  in  connection  with  a  function, 
such  as  digestion  or  secretion,  which  belongs  to  all  organized  beings 
alike;  while  the  term  animal  function,  or  animal  life,  is  used  in  con- 
nection with  such  qualities  as  volition  or  motion,  which  seem  alto- 
gether or  in  great  part  to  belong  only  to  animals.  The  terms  which 
have  been  thus  used  in  this  general  way,  are  often  loosely  applied  to 
special  tissues.  Thus  organic  nerve-fibres  are  those  which  are  dis- 
tributed especially  to  organs  concerned  in  the  discharge  of  the  func- 
tions of  organic,  as  distinguished  from  animal  life  ;  and  the  term  is 
still  more  commonly  applied  to  one  kind  of  muscular  fibre. 


STRUCTURE     OF     NERVE- FIB  RES. 


369 


FIG.  133. 
B  c 


Along  the  nerve-fibres  impressions  or  conditions  of  excite- 
ment are  simply  conducted :  in  the  nervous  centres  they  may 
be  made  to  deviate  from  their  direct  course,  and  be  variously 
diffused,  reflected,  or  otherwise  disposed  of. 

Nerves  are  constructed  of  minute  fibres  or  tubules  full  of 
nervous  matter,  arranged  in  parallel  or  interlacing  bundles, 
which  bundles  are  connected  by  intervening  connective  tissue, 
in  which  their  principal  bloodvessels  ramify.  A  layer  of  the 
areolar,  or  of  strong  fibrous  tissue,  also  surrounds  the  whole 
nerve,  and  forms  a  sheath  or  neurilemma  for  it.  In  most 
nerves,  two  kinds  of  fibres  are  mingled ;  those  of  one  kind 
being  most  numerous  in,  and  charac- 
teristic of,  nerves  of  the  cerebro- 
spinal  system ;  those  of  the  other, 
most  numerous  in  nerves  of  the 
sympathetic  system. 

The  fibres  of  the  first  kind  appear 
to  consist  of  tubules  of  a  pellucid 
simple  membrane,  within  which  is 
contained  the  proper  nerve  sub- 
stance, consisting  of  transparent  oil- 
like,  and  apparently  homogeneous 
material,  which  gives  to  each  fibre 
the  appearance  of  a  fine  glass  tube 
filled  with  a  clear  transparent  fluid 
(Fig.  133,  A).  This  simplicity  of 
composition  is,  however,  only  ap- 
parent in  the  fibres  of  a  perfectly 
fresh  nerve ;  for  shortly  after  death, 
they  undergo  changes  which  make 
it  probable  that  their  contents  are 
composed  of  two  different  materials. 
The  internal  or  central  part,  occu- 
pying the  axis  of  the  tube,  becomes 
grayish,  while  the  outer,  or  cortical 
portion,  becomes  opaque  and  dimly 
granular  or  grumous,  as  if  from  a 
kind  of  coagulation.  At  the  same 
time,  the  fine  outline  of  the  pre- 
viously transparent  cylindrical  tube 
is  exchanged  for  a  dark  double  con- 
tour (Fig.  133,  B),  the  outer  line 
being  formed  by  the  sheath  of  the 
fibre,  the  inner  by  the  margin  of 
curdled  or  coagulated  medullary  substance.  The  granular 


Primitive  nerve-tubules.  A. 
A  perfectly  fresh  tubule  with 
a  single  dark  outline.  B.  A 
tubule  or  fibre  with  a  double 
contour  from  commencing 
post-mortem  change,  c.  The 
changes  further  advanced, 
producing  a  varicose  or  beaded 
appearance.  D.  A  tubule  or 
fibre,  the  central  part  of  which, 
in  consequence  of  still  further 
changes,  has  accumulated  in 
separate  portions  within  the 
sheath  (after  Wagner). 


370  THE    NERVOUS    SYSTEM. 

material  shortly  collects  into  little  masses,  which  distend  por- 
tions of  the  tubular  membrane,  while  the  intermediate  spaces 
collapse,  giving  the  fibres  a  varicose,  or  beaded  appearance 
(Fig.  133  c  and  D),  instead  of  the  previous  cylindrical  form. 

The  difference  produced  in  the  contents  of  the  nerve-fibres 
when  exposed  to  the  same  conditions,  has,  with  other  facts,  led 
to  the  opinion  now  generally  adopted,  that  the  central  part  or 
axis-cylinder  of  each  nerve-fibre  differs  from  the  outer  portion. 
The  outer  portion  is  usually  called  the  medullary  or  white  sub- 
stance of  Schwann,  being  that  to  which  the  peculiar  white 
aspect  of  cerebro-spinal  nerves  is  principally  due.  The  whole 
contents  of  the  nerve-tubules  appear  to  be  extremely  soft,  for 
when  subjected  to  pressure  they  readily  pass  from  one  part  of 
the  tubular  sheath  to  another,  and  often  cause  a  bulging  at  the 
side  of  the  membrane.  They  also  readily  escape,  on  pressure, 
from  the  extremities  of  the  tubule,  in  the  form  of  a  grumous  or 
granular  material. 

That  there  is  an  essential  difference  in  chemical  composition 
between  the  central  and  circumferential  parts  of  the  nerve- 
fibre,  i.  e.,  between  the  axis-cylinder  and  the  medullary  sheath, 
has  of  late  been  clearly  shown  by  Messrs.  Lister  and  Turner. 
Their  observations,  founded  on  Mr.  Lockhart  Clarke's  method 
of  investigating  nervous  substance  by  means  of  chromic  acid 
and  carmine,  have  shown  that  the  axis-cylinder  of  the  nerve- 
fibre  is  unaffected  by  chromic  acid,  but  imbibes  carmine  with 
great  facility,  while  the  medullary  sheath  is  rendered  opaque 
and  brown  and  laminated  by  chromic  acid,  but  is  entirely  un- 
tinged  by  the  carmine.  From  this  difference  in  their  chemi- 
cal behavior,  the  central  and  circumferential  portions  of  the 
nerve-fibres  are  readily  distinguished  on  microscopic  examina- 
tion, the  former  being  indicated  by  a  bright  red  carmine- 
colored  point,  the  latter  by  a  pale  ring  surrounding  it.  The 
laminated  character  of  the  medullary  sheath  after  treatment 
with  chromic  acid  is  believed  by  Mr.  Lockhart  Clarke  to  be 
due  to  corrugations  effected  by  the  acid,  and  not  to  its  having 
a  fibrous  structure,  as  maintained  by  Stilling. 

The  size  of  the  nerve-fibres  varies,  and  the  same  fibres  do 
not  preserve  the  same  diameter  through  their  whole  length, 
being  largest  in  their  course  within  the  trunks  and  branches  of 
the  nerves,  in  which  the  majority  measure  from  ^oo  to  sf/ou 
of  an  inch  in  diameter.  As  they  approach  the  brain  or  spinal 
cord,  and  generally  also  in  the  tissues  in  which  they  are  dis- 
tributed, they  gradually  become  smaller.  In  the  gray  or  vesic- 
ular substance  of  the  brain  or  spinal  cord,  they  generally  do 
not  measure  more  than  from  y^Joo  to  T¥fi<r<J  °f  an  mcn- 

The  fibres  of  the  second  kind  (Fig.  134),  which  constitute 


COURSE    OF    NERVE-FIBRES.  371 

the  whole  of  the  branches  of  the  olfactory  nerves,  the  principal 
part  of  the  trunk  and  branches  of  the  sympathetic  nerves,  and 
are  mingled  in  various  proportions  in  the  cerebro-spinal  nerves, 
differ  from  the  preceding,  chiefly  in  their  fineness,  being  only 
about  J  or  £  as  large  in  their  course  within  the  trunks  and 

FIG.  134. 
A 


Gray,  pale,  or  gelatinous  nerve-fibres  (from  Max  Schultze),  magnified  between  400 
and  500  diameters.  A.  From  a  branch  of  the  olfactory  nerve  of  the  sheep ;  tt,  a,  two 
dark-bordered  or  white  fibres  from  the  fifth  pair,  associated  with  the  pale  olfactory 
fibres.  B.  From  the  sympathetic  nerve. 

branches  of  the  nerves;  in  the  absence  of  the  double  contour; 
in  their  contents  being  apparently  uniform ;  and  in  their 
having,  when  in  bundles,  a  yellowish-gray  hue  instead  of  the 
whiteness  of  the  cerebro-spinal  nerves.  These  peculiarities 
make  it  probable  that  they  differ  from  the  other  nerve-fibres 
in  not  possessing  the  outer  layer  of  white  or  medullary  nerve- 
substance  ;  and  that  their  contents  are  composed  exclusively 
of  the  substance  corresponding  with  the  central  portion,  or 
axis-cylinder  of  the  larger  fibres.  Yet  since  many  nerve-fibres 
may  be  found  which  appear  intermediate  in  character  between 
these  two  kinds,  and  since  the  large  fibres,  as  they  approach 
both  their  central  and  their  peripheral  end,  gradually  dimmish 
in  size,  and  assume  many  of  the  other  characters  of  the  fine 
fibres  of  the  sympathetic  system,  it  is  not  necessary  to  suppose 
that  there  must  be  a  material  difference  in  the  office  or  mode 
of  action  of  the  two  kinds  of  fibres. 

Every  nerve-fibre  in  its  course  proceeds  uninterruptedly  from 
its  origin  at  a  nervous  centre  to  near  its  destination,  whether 
this  be  the  periphery  of  the  body,  another  nervous  centre,  or 
the  same  centre  whence  it  issued. 

Bundles,  or  fasciculi  of  fibres,  run  together  in  the  nerves, 


372 


THE    NERVOUS    SYSTEM. 


but  merely  lie  in  apposition  with  each  other ;  they  do  not  unite ; 
even  when  the  fasciculi  anastomose,  there  is  no  union  of  fibres, 
but  only  an  interchange  of  fibres  between  the  anastomosing 
fasciculi.  Although  each  nerve-fibre  is  thus  single  and  undi- 
vided through  nearly  its  whole  course,  yet  as  it  approaches  the 
region  in  which  it  terminates,  individual  fibres  break  up  into 
several  subdivisions  (Fig.  135)  before  their  final  ending  in  the 

FIG.  135. 


Small  branch  of  a  muscular  nerve  of  the  frog,  near  its  termination,  showing  divi- 
sions of  the  fibres,  a,  into  two ;  b,  into  three ;  magnified  350  diameters  (from  K61- 
liker). 

different  fashions  to  be  immediately  described.  The  white  or 
medullated  nerve-fibres  (Fig.  133),  moreover,  lose  their  medul- 
lary sheath  or  white  substance  of  Schwann  before  their  final 
distribution,  and  acquire  the  characters  more  or  less  of  the 
pale  or  gray  fibres  (Fig.  134). 

At  certain  parts  of  their  course,  nerves  form  plexuses,  in 
which  they  anastomose  with  each  other,  and  interchange  fas- 
ciculi, as  in  the  case  of  the  brachial  and  lumbar  plexuses. 
The  object  of  such  interchange  of  fibres  is,  probably,  to  give 
to  each  nerve  passing  off  from  the  plexus,  a  wider  connection 


PACINIAN     BODIES.  373 

with  the  spinal  cord  than  it  would  have  if  it  proceeded  to  its 
destination  without  such  communication  with  other  nerves. 
Thus,  each  nerve  by  the  wideness  of  its  connections,  is  less  de- 
pendent on  the  integrity  of  any  single  portion,  whether  of 
nerve-centre  or  of  nerve-trunk,  from  which  it  may  spring.  By 
this  means,  also,  each  part  supplied  from  a  plexus  has  wider 
relations  with  the  nerve-centres,  and  more  extensive  sympa- 
thies; and,  by  means  of  the  same  arrangement,  as  Dr.  Gull 
suggests,  groups  of  muscles  may  be  associated  for  combined 
actions;  every  member  of  the  group  receiving  motor  filaments 
from  the  same  parts  of  the  nerve-centre. 

The  terminations  of  nerve-fibres  are  their  modes  of  distribu- 
tion and  connection  in  the  nerve-centres,  and  in  the  parts 
which  they  supply:  the  former  are  called  their  central,  the 
latter  their  peripheral  terminations. 

The  peripheral  termination  of  nerve-fibres  has  been  always 
the  subject  of  considerable  discussion  and  doubt.  The  follow- 
ing appear  to  be  the  chief  modes  of  ending  of  nerve  fibres  in 
the  parts  they  supply  : 

1.  In  fine  networks  or  plexuses ;  examples  of  this  are  found 
in  the  distribution  of  nerves  in  muscles,  and  in  mucous  and 
serous  membranes.  2.  In  special  terminal  organs,  called 
touch-corpuscles  (Fig.  113),  end-bulbs  (Fig.  114),  and  Pacinian 
bodies  (Figs.  136,  137).  3.  In  cells ;  as  in  the  eye  and  inter- 
nal ear,  and  some  other  parts.  4.  In  free  ends ;  as  from  the 
fine  plexuses  in  muscles,  according  to  Kolliker.  5.  In  mus- 
cles, a  peculiar  termination  of  nerves  in  small  bodies  called 
motorial  end-plates,  has  been  described  by  Rouget  and  others. 
These  small  bodies,  varying  from  ^'g^  to  ^-5-^  of  an  inch  in 
diameter,  and  placed  by  different  observers  outside  and  inside 
the  sarcolemma,  are  fixed  to  the  muscular  fibres,  one  for  each, 
and  to  them  the  extremity  of  a  minute  branch  of  nerve-fibre 
is  attached.  These  little  plates  appear  to  be  formed  of  an 
expansion  of  the  end  of  a  nerve-fibre  with  a  small  quantity  of 
connective  tissue. 

The  Pacinian  bodies  or  corpuscles  (Figs.  136  and  137),  to 
which  reference  has  been  just  made,  are  little  elongated  oval 
bodies,  situated  on  some  of  the  cerebro-spinal  and  sympathetic 
nerves,  especially  the  cutaneous  nerves  of  the  hands  and  feet ; 
and  on  branches  of  the  large  sympathetic  plexus  about  the 
abdominal  aorta  (Kolliker).  They  often  occur  also  on  the 
nerves  of  the  mesentery,  and  are  especially  well  seen  in  the 
mesentery  of  the  cat.  They  are  named  Pacinian,  after  their 
discoverer  Pacini.  Each  corpuscle  is  attached  by  a  narrow 
pedicle  to  the  nerve  on  which  it  is  situated ;  it  is  formed  of 
several  concentric  layers  of  fine  membrane,  with  intervening 

32 


374 


THE    NERVOUS    SYSTEM. 


spaces  containing  fluid  ;  through  its  pedicle  passes  a  single 
nerve-fibre,  which,  after  traversing  the  several  concentric 
layers  and  their  immediate  spaces,  enters  a  central  cavity,  and, 
gradually  losing  its  dark  border,  and  becoming  smaller,  ter- 


Fio.  137. 


FIG.  136. 


FIG.  136. — Extremities  of  a  nerve  of  the  finger  with  Pacinian  corpuscles  attached. 
A.  Nerve  from  the  finger,  natural  size  ;  showing  the  Pacinian  corpuscles.  B.  Ditto, 
magnified  two  diameters,  showing  their  different  size  and  shape. 

FIG.  137. — Pacinian  corpuscles  from  the  mesentery  of  a  cat ;  intended  to  show  the 
general  construction  of  these  bodies.  The  stalk  and  body,  the  outer  and  inner 
system  of  capsules  with  the  central  cavity  are  seen.  a.  Arterial  twig,  ending  in 
capillaries,  which  form  loops  in  some  of  the  intercapsular  spaces,  and  one  penetrates 
to  the  central  capsule,  b.  The  fibrous  tissue  of  the  stalk,  prolonged  from  the  neuri- 
lemma.  n.  Nerve-tube  advancing  to  the  central  capsule,  there  losing  its  white  sub- 
stance, and  stretching  along  the  axis  to  the  opposite  end,  where  it  is  fixed  by  a 
tubercular  enlargement. 


minates  at  or  near  the  distal  end  of  the  cavity,  in  a  knob-like 
enlargement,  or  in  a  bifurcation.  The  enlargement  commonly 
found  at  the  end  of  the  fibre,  is  said  bv  Pacini  to  resemble  a 


STRUCT  U  BE    OF     NERVE-CENTRES. 


375 


FIG.  138. 


fanglion-corpuscle  ;  but  this  observation  has  not  been  con- 
rmed.     The  physiological  import  of  these  bodies  seems  to  be 
still  quite  obscure. 

The  central  termination  of  nerve-fibres  can  be  better  con- 
sidered after  the  account  of  the  vesicular  nerve-substance. 

The  vesicular  nervous  substance  contains,  as  its  name  implies, 
vesicles  or  corpuscles,  in  addition  to  fibres ;  and  a  structure, 
thus  composed  of  corpuscles  and  intercommunicating  fibres, 
usually  constitutes  a  nerve-centre :  the  chief  nerve-centres  being 
the  gray  matter  of  the  brain  and  spinal  cord,  and  the  various 
so-called  ganglia.  In  the  brain  and  spinal  cord  a  fine  stroma 
of  retiform  tissue  called  the  neuroglia  extends  throughout  both 
the  fibrous  and  vesicular  ner- 
vous substance,  and  forms  a  sup- 
porting and  investing  frame- 
work for  the  whole. 

The  nerve-corpuscles,  which 
give  to  the  ganglia  and  to  cer- 
tain parts  of  the  brain  and  spi- 
nal cord  the  peculiar  grayish  or 
reddish-gray  aspect  by  which 
these  parts  are  characterized, 
are  large,  nucleated  cells,  filled 
with  a  finely  granular  material, 
some  of  which  is  often  dark  like 
pigment :  the  nucleus,  which  is 
vesicular,  contains  a  nucleolus 
(Fig.  138).  Besides  varying  much  in  shape,  partly  in  conse- 
quence of  mutual  pressure,  they  present  such  other  varieties 
as  make  it  probable  either  that  there  are  two  different  kinds, 
or  that,  in  the  stages  of  their  development,  they  pass  through 
very  different  forms.  Some  of  them  are  small,  generally 
spherical  or  ovoid,  and  have  a  regular  uninterrupted  outline 
(Fig.  138).  These  simple  nerve-corpuscles  are  most  numerous 
in  the  sympathetic  ganglia.  Others,  which  are  called  caudate 
or  stellate  nerve-corpuscles  (Fig.  139),  are  larger,  and  have  one, 
two,  or  more  long  processes  issuing  from  them,  the  cells  being 
called  respectively  unipolar,  bipolar,  or  multipolar ;  which  pro- 
cesses often  divide  and  subdivide,  and  appear  tubular,  and  filled 
with  the  same  kind  of  granular  material  that  is  contained 
within  the  corpuscle.  Of  these  processes  some  appear  to  taper 
to  a  point  and  terminate  at  a  greater  or  less  distance  from  the 
corpuscle ;  some  appear  to  anastomose  with  similar  offsets 
from  other  corpuscles ;  while  others  are  believed  to  become 
continuous  with  nerve-fibres,  the  prolongation  from  the  cell 


Nerve-corpuscles  from  a  ganglion 
(after  Valentin).  In  one  a  second  nu- 
cleus is  •visible.  In  several  the  nu- 
cleus contains  one  or  two  nucleoli. 


376 


THE    NERVOUS    SYSTEM. 


by  degrees  assuming  the  characters  of  the  nerve-fibre  with 
which  it  is  continuous. 


c  D  E 

Various  forms  of  ganglionic  vesicles :  A,  B,  large  stellate  cells,  with  their  prolon- 
gations, from  the  anterior  horn  of  the  gray  matter  of  the  spinal  cord ;  c,  nerve-cell 
with  its  connected  fibre,  from  the  anastomosis  of  the  facial  and  auditory  nerves  in 
the  meatus  auditorius  internus  of  the  ox  ;  a,  cell-wall ;  b,  cell-contents;  c,  pigment; 
d,  nucleus ;  e,  prolongation  forming  the  sheath  of  the  fibre ;  /,  nerve-fibre  ;  D,  nerve- 
cell  from  the  substantia  ferruginea  of  man  ;  E,  smaller  cell  from  the  spinal  cord, 
magnified  350  diameters. 


Functions  of  Nerve-Fibres. 

The  office  of  the  nerves  as  simple  conveyers  or  conductors 
of  nervous  impressions  is  of  a  twofold  kind.  First,  they  serve 
to  convey  to  the  nervous  centres  the  impressions  made  upon 
their  peripheral  extremities,  or  parts  of  their  course.  Sec- 
ondly, they  serve  to  transmit  impressions  from  the  brain  and 
other  nervous  centres  to  the  parts  to  which  the  nerves  are 
distributed. 

For  this  twofold  office  of  the  nerves,  two  distinct  sets  of 
nerve-fibres  are  provided,  in  both  the  cerebro-spinal  and  sym- 
pathetic systems.  Those  which  convey  impressions  from  the 
periphery  to  the  centre  are  classed  together  as  centripetal  or 
afferent  nerves.  Those  fibres,  on  the  other  hand,  which  are 
employed  to  transmit  central  impulses  to  the  periphery  are 
classed  as  centrifugal  or  efferent  nerves. 

Centripetal  or  afferent  nerve-fibres  may  (a)  convey  to  the 
nerve-centres  with  which  they  are  connected  impressions  which 


FUNCTIONS    OF     NERVE-FIBRES.  377 

will  give  rise  to  sensation  (sensitive  nerves),  or  (6)  they  may 
convey  an  impression  which  travels  out  again  from  the  nerve- 
centre  by  an  efferent  nerve-fibre,  and  produces  some  effect 
where  the  latter  is  distributed  (see  section  on  Reflex  Action), 
or  (c)  they  may  convey  an  impression  which  will  produce  a 
restraining  or  inhibitory  action  in  the  nerve-centre  (inhibitory 
nerves,  p.  113). 

Centrifugal  or  efferent  nerves  may  be  (a)  for  the  convey- 
ance of  impulses  to  the  voluntary  and  involuntary  muscles, 
(motor  nerves),  or  (6)  they  may  influence  nutrition  (trophic 
nerves),  (p.  310),  or  (c)  they  may  influence  secretion  (some- 
times called  secretory  nerves)  (p.  325). 

With  this  difference  in  the  functions  of  nerves,  there  is  no 
apparent  difference  in  the  structure  of  the  nerve-fibres  by 
which  it  might  be  explained.  Among  the  cerebro-spinal  nerves, 
the  fibres  of  the  optic  and  auditory  nerves  are  finer  than  those 
of  the  nerves  of  common  sensation ;  but,  with  these  exceptions, 
no  centripetal  fibres  can  be  distinguished  in  their  microscopic 
or  general  characters  from  those  of  centrifugal  nerves. 

Nerve-fibres  possess  no  power  of  generating  force  in  them- 
selves, or  of  originating  impulses  to  action  :  for  the  manifesta- 
tion of  their  peculiar  endowments  they  require  to  be  stimu- 
lated. They  possess  a  certain  property  of  conducting  impres- 
sions, a  property  which  has  been  named  excitability ;  but  this 
is  never  manifested  till  some  stimulus  is  applied.  Thus,  under 
ordinary  circumstances,  nerves  of  sensation  are  stimulated  by. 
external  objects  acting  upon  their  extremities ;  and  nerves  of 
motion  by  the  will,  or  by  some  force  generated  in  the  nervous 
centres.  But  almost  all  things  that  can  disturb  the  nerves 
from  their  passive  state  act  as  stimuli,  and  agents  the  most 
dissimilar  produce  the  same  kind,  though  not  the  same  degree 
of  effect,  because  that  on  which  they  act  possesses  but  one 
kind  of  excitable  force.  Thus  all  stimuli — chemical,  me- 
chanical, and  electric, — when  applied  to  parts  endowed  with 
sensation,  or  to  sensitive  nerves  (the  connection  of  the  latter 
with  the  brain  and  spinal  cord  being  uninjured)  produce  sen- 
sations ;  and  when  applied  to  the  nerves  of  muscles  excite  con- 
tractions. Muscular  contraction  is  produced  by  such  stimuli 
as  well  when  the  motor  nerve  is  still  in  connection  with  the 
brain,  as  when  its  communication  with  the  nervous  centres  is 
cut  off  by  dividing  it ;  nerves,  therefore,  have,  by  virtue  of 
their  excitability,  the  property  of  exciting  contractions  in 
muscles  to  which  they  are  distributed ;  and  the  part  of  the 
divided  motor  nerve  which  is  connected  with  the  muscle  will 
still  retain  this  power,  however  much  we  may  curtail  it. 

Mechanical  irritation,  when  so  violent  as  to  injure  the  tex- 


378  THE     NERVOUS    SYSTEM. 

ture  of  the  primitive  nerve-fibres,  deprives  the  centripetal 
nerves  of  their  power  of  producing  sensations  when  irritation 
is  again  applied  at  a  point  more  distant  from  the  brain  than 
the  injured  spot;  and  in  the  same  way,  no  irritation  of  a 
motor  nerve  will  excite  contraction  of  the  muscle  to  which  it 
is  distributed,  if  the  nerve  has  been  compressed  and  bruised 
between  the  point  of  irritation  and  the  muscle ;  the  effect  of 
such  an  injury  being  the  same  as  that  of  division. 

The  action  of  nerves  is  also  excited  by  temperature.  Thus, 
when  heat  is  applied  to  the  nerve  going  to  a  muscle,  or  to  the 
muscle  itself,  contractions  are  produced.  These  contractions  are 
very  violent  when  the  flame  of  a  candle  is  applied  to  the  nerve, 
while  less  elevated  degrees  of  heat, — for  example,  that  of  a  piece 
of  iron  merely  warmed, — do  not  irritate  sufficiently  to  excite 
action  of  the  muscles.  The  application  of  cold  has  the  same 
effect  as  that  of  heat.  The  effect  of  the  local  action  of  excessive 
or  long-continued  cold  or  heat  on  the  nerves  is  the  same  as  that 
of  destructive  mechanical  irritation.  The  sensitive  and  motor 
power  in  the  part  is  destroyed,  but  the  other  parts  of  the 
nerve  retain  their  excitability ;  and,  after  the  extremity  of  a 
divided  nerve  going  to  a  muscle  has  been  burnt,  contractions 
of  the  muscle  may  be  excited  by  irritating  the  nerve  below 
the  burnt  part. 

Chemical  Stimuli  excite  the  action  of  both  afferent  and  ef- 
ferent nerves  as  mechanical  irritants  do;  provided  their  effect 
is  not  so  strong  as  to  destroy  the  structure  of  the  nerve  to  which 
they  are  applied.  A  like  manifestation  of  nervous  power  is 
produced  by  electricity  and  by  magnetism. 

Some  of  these  laws  regulating  the  excitability  of  nerves,  and 
their  power  of  manifesting  their  functions,  require  further 
notice,  with  several  others  which  have  not  yet  been  alluded 
to.  Certain  of  the  laws  and  conditions  of  actions  relate  to 
nerves  both  centrifugal  and  centripetal,  being  dependent  on 
properties  common  to  all  nerve-fibres;  while  of  others,  some 
are  peculiar  to  nerves  of  motion,  some  to  nerves  of  sensation. 

It  is  a  law  of  action  in  all  nerve-fibres,  and  corresponds 
with  the  continuity  and  simplicity  of  their  course,  that  an  im- 
pression made  on  any  fibre,  is  simply  and  uninterruptedly 
transmitted  along  it,  without  being  imparted  or  diffused  to  any 
of  the  fibres  lying  near  it.  In  other  words,  all  nerve-fibres  are 
mere  conductors  of  impressions.  Their  adaptation  to  this  pur- 
pose is,  perhaps,  due  to  the  contents  of  each  fibre  being  com- 
pletely isolated  from  those  of  adjacent  fibres  by  the  membrane 
or  sheath  in  which  each  is  inclosed,  and  which  acts,  it  may  be 
supposed,  just  as  silk,  or  other  non-conductors  of  electricity  do, 


FUNCTIONS    OF     NER  VE  -  F  I  B  R  ES.  379 

which,  when  covering  a  wire,  prevent  the  electric  condition  of 
the  wire  from  being  conducted  into  the  surrounding  medium. 

Nervous  force  travels  along  nerve-fibres  with  considerable 
velocity.  Helmholtz  and  Baxt  have  estimated  the  average 
rate  of  conduction  of  electrical  impressions  in  human  motor 
nerves  at  111  feet  per  second:  this  result  agreeing  very  closely 
with  that  previously  obtained  by  Hirsch.  Dr.  Rutherford's 
observations  agree  with  those  of  Von  Wittich,  that  the  rate 
of  transmission  in  sensory  nerves  is  about  140  feet  per  second. 

Nerve-fibres  convey  only  one  kind  of  impression.  Thus,  a 
motor  fibre  conveys  only  motor  impulses,  that  is,  such  as  may 
produce  movements  in  contractile  parts:  a  sensitive  fibre  trans- 
mits none  but  such  as  may  produce  sensation,  if  they  are  propa- 
gated to  the  brain.  Moreover,  the  fibres  of  a  nerve  of  special 
sense,  as  the  optic  or  auditory,  convey  only  such  impressions 
as  may  produce  a  peculiar  sensation,  e.  g.,  that  of  light  or 
sound.  While  the  rays  of  light  and  the  sonorous  vibrations 
of  the  air,  are  without  influence  on  the  nerves  of  common  sen- 
sation, the  other  stimuli,  which  may  produce  pain  when  applied 
to  them,  produce  when  applied  to  these  nerves  of  special  sense, 
only  morbid  sensations  of  light,  or  sound,  or  taste,  according  to 
the  nerve  impressed. 

Of  the  laws  of  action  peculiar  to  nerves  of  sensation  and  of 
motion  respectively,  many  can  be  ascertained  only  by  experi- 
ments on  the  roots  of  the  nerves.  For  it  is  only  at  their  origin 
that  the  nerves  of  sensation  and  of  motion  are  distinct;  their 
filaments,  shortly  after  their  departure  from  the  nervous  cen- 
tres, are  mingled  together,  so  that  nearly  all  nerves,  except 
those  of  the  special  senses,  consist  of  both  sensitive  and  motor 
filaments,  and  are  hence  termed  mixed  nerves. 

Nerves  of  sensation  appear  able  to  convey  impressions  only 
from  the  parts  in  which  they  are  distributed,  towards  the  nerve- 
centre  from  which  they  arise,  or  to  which  they  tend.  Thus, 
when  a  sensitive  nerve  is  divided,  and  irritation  is  applied  to 
the  end  of  the  proximal  portion,  i,  e.,  of  the  portion  still  con- 
nected with  the  nervous  centre,  sensation  is  perceived,  or  a 
reflex  action  ensues;  but,  when  the  end  of  the  distal  portion  of 
the  divided  nerve  is  irritated,  no  effect  appears. 

When  an  impression  is  made  upon  any  part  of  the  course  of 
a  sensitive  nerve,  the  mind  may  perceive  it  as  if  it  were  made 
not  only  upon  the  point  to  which  the  stimulus  is  applied,  but 
also  upon  all  the  points  in  which  the  fibres  of  the  irritated 
nerve  are  distributed :  in  other  words,  the  effect  is  the  same  as 
if  the  irritation  were  applied  to  the  parts  supplied  by  the 
branches  of  the  nerve.  When  the  whole  trunk  of  the  nerve 


380  THE     NERVOUS    SYSTEM. 

is  irritated,  the  sensation  is  felt  at  all  the  parts  which  receive 
branches  from  it;  but  when  only  individual  portions  of  the 
trunk  are  irritated,  the  sensation  is  perceived  at  those  parts 
only  which  are  supplied  by  the  several  portions.  Thus,  if  we 
compress  the  ulnar  nerve  where  it  lies  at  the  inner  side  of  the 
elbow-joint,  behind  the  internal  condyle,we  have  the  sensation 
of  "  pins  and  needles,"  or  of  a  shock,  in  the  parts  to  which  its 
fibres  are  distributed,  namely,  in  the  palm  and  back  of  the 
hand,  and  in  the  fifth  and  ulnar  half  of  the  fourth  finger. 
When  stronger  pressure  is  made,  the  sensations  are  felt  in  the 
forearm  also ;  and  if  the  mode  and  direction  of  the  pressure  be 
varied,  the  sensation  is  felt  by  turns  in  the  fourth  finger,  in  the 
fifth,  and  in  the  palm  of  the  hand,  or  in  the  back  of  the  hand, 
according  as  different  fibres  or  fasciculi  of  fibres  are  more 
pressed  upon  than  others. 

It  is  in  accordance  with  this  law,  that  when  parts  are  de- 
prived of  sensibility  by  compression  or  division  of  the  nerve 
supplying  them,  irritation  of  the  portion  of  the  nerve  connected 
with  the  brain  still  excites  sensations  which  are  felt  as  if  de- 
rived from  the  parts  to  which  the  peripheral  extremities  of  the 
nerve-fibres  are  distributed.  Thus,  there  are  cases  of  paralysis 
in  which  the  limbs  are  totally  insensible  to  external  stimuli, 
yet  are  the  seat  of  most  violent  pain,  resulting  apparently  from 
irritation  of  the  sound  part  of  the  trunk  of  the  nerve  still  in 
connection  with  the  brain,  or  from  irritation  of  those  parts  of 
the  nervous  centre  from  which  the  sensitive  nerve  or  nerves 
which  supply  the  paralyzed  limbs  originate. 

An  illustration  of  the  same  law  is  also  afforded  by  the  cases 
in  which  division  of  a  nerve  for  the  cure  of  neuralgic  pain  is 
found  useless,  and  in  which  the  pain  continues  or  returns, 
though  portions  of  the  nerve  be  removed.  In  such  cases,  the 
disease  is  probably  seated  nearer  the  nervous  centre  than  the 
part  at  which  the  division  of  the  nerve  is  made,  or  it  may  be 
in  the  nervous  centre  itself.  When  the  cause  of  the  neuralgia 
is  seated  in  the  trunk  of  the  nerve — for  example,  of  the  facial 
or  infraorbital  nerve — division  of  the  branches  can  be  of  no 
service;  for  the  stump  remaining  in  connection  with  the  brain, 
and  containing  all  the  fibres  distributed  in  the  branches  of  the 
nerve  to  the  skin,  continues  to  give  rise,  when  irritated,  to  the 
same  sensations  as  are  felt  when  the  peripheral  parts  themselves 
are  affected.  Division  of  a  nerve  prevents  the  possibility  of 
external  impressions  on  the  cutaneous  extremities  of  its  fibre 
being  felt;  for  these  impressions  can  no  longer  be  communi- 
cated to  the  brain :  but  the  same  sensations  which  were  before 
produced  by  external  impressions  may  arise  from  internal 
causes.  In  the  same  way  may  be  explained  the  fact,  that  when 


FUNCTIONS    OF     NERVE-FIBRES.  381 

part  of  a  limb  has  been  removed  by  amputation,  the  remaining 
portions  of  the  nerves  which  ramified  in  it  may  give  rise  to 
sensations  which  the  mind  refers  to  the  lost  part.  When  the 
stump  and  the  divided  nerves  are  inflamed,  or  pressed,  the 
patient  complains  of  pain  felt  as  if  in  the  part  which  has  been 
removed.  When  the  stump  is  healed,  the  sensations  which  we 
are  accustomed  to  have  in  a  sound  limb  are  still  felt;  and 
tingling  and  pains  are  referred  to  the  parts  that  are  lost,  or  to 
particular  portions  of  them,  as  to  single  toes,  to  the  sole  of  the 
foot,  to  the  dorsum  of  the  foot,  &c. 

But  (as  Volkmann  shows)  it  must  not  be  assumed,  as  it 
often  has  been,  from  these  examples,  that  the  mind  has  no 
power  of  discriminating  the  very  point  in  the  length  of  any 
nerve-fibre  to  which  an  irritation  is  applied.  Even  in  the  in- 
stances referred  to,  the  mind  perceives  the  pressure  of  a  nerve 
at  the  point  of  pressure,  as  well  as  in  the  seeming  sensations 
derived  from  the  extremities  of  the  fibres ;  and  in  stumps, 
pain  is  felt  in  the  stump,  as  well  as,  seemingly,  in  the  parts 
removed.  It  is  not  quite  certain  whether  those  sensations  are 
perceived  by  the  nerve-fibres  which  are  on  their  way  to  be 
distributed  elsewhere,  or  by  the  sentient  extremities  of  nerves 
which  are  themselves  distributed  to  the  many  trunks  of  the 
nerves,  the  nervi  nervorum.  The  latter  is  the  more  probable 
supposition. 

The  habit  of  the  mind  to  refer  impressions  received  through 
the  sensitive  nerves  to  the  parts  from  which  impressions 
through  those  nerves  are,  or  were,  commonly  received,  is  fur- 
ther exemplified  when  the  relative  position  of  the  peripheral 
extremities  of  sensitive  nerves  is  changed  artificially,  as  in  the 
transposition  of  portions  of  skin.  When  in  the  restoration  of  a 
nose,  a  flap  of  skin  is  turned  down  from  the  forehead  and  made 
to  unite  with  the  stump  of  the  nose,  the  new  nose  thus  formed 
has,  as  long  as  the  isthmus  of  skin  by  which  it  maintains  its 
original  connections  remains  undivided,  the  same  sensations  as 
if  it  were  still  on  the  forehead ;  in  other  words,  when  the  nose 
is  touched,  the  patient  feels  the  impression  as  if  it  were  made 
on  the  forehead.  When  the  communication  of  the  nervous 
fibres  of  the  new  nose  with  those  of  the  forehead  is  cut  off  by 
division  of  the  isthmus  of  skin,  the  sensations  are  no  longer 
referred  to  the  forehead ;  the  sensibility  of  the  nose  is  at  first 
absent,  but  is  gradually  developed. 

When,  in  a  part  of  the  body  which  receives  two  sensitive 
nerves,  one  is  paralyzed,  the  other  may  or  may  not  be  inadequate 
to  maintain  the  sensibility  of  the  entire  part ;  the  extent  to 
which  the  sensibility  is  preserved  corresponding  probably  with 
the  number  of  the  fibres  unaffected  by  the  paralysis.  Thus 


382  THE     NERVOUS    SYSTEM. 

when  the  ulnar  nerve,  which  supplies  the  fifth  and  a  part  of 
the  fourth  finger,  is  divided,  the  sensibility  of  those  parts  is 
not  preserved  through  the  medium  of  the  branches  which  the 
ulnar  derives  from  the  median  nerve ;  but  the  fourth  and  fifth 
fingers  are  permanently  deprived  of  sensibility.  On  the  other 
hand,  there  are  instances  in  which  the  trunk  of  the  chief  sen- 
sitive nerve  supplied  to  a  part  having  been  divided,  the  sensi- 
bility of  the  part  is  still  preserved  by  intercommunicating 
fibres  from  a  neighboring  nerve-trunk.  Thus,  a  case  is  related 
by  Mr.  Savory  in  which,  after  excision  of  a  portion  of  the 
musculo-spiral  nerve,  the  sensibility  of  some  of  the  parts  sup- 
plied by  it,  although  impaired,  was  not  altogether  lost,  prob- 
ably on  account  of  those  fibres  from  the  external  cutaneous 
nerve  which  are  mingled  with  the  radial  branch  of  the  mus- 
culo-spiral. One  of  the  uses  of  a  nervous  plexus  (p.  372)  is 
here  well  illustrated. 

Several  of  the  laws  of  action  in  motor  nerves  correspond 
with  the  foregoing.  Thus,  the  motor  influence  is  propagated 
only  in  the  direction  of  the  fibres  going  to  the  muscles ;  by 
irritation  of  a  motor  nerve,  contractions  are  excited  in  all  the 
muscles  supplied  by  the  branches  given  off  by  the  nerve 
below  the  point  irritated,  and  in  those  muscles  alone :  the 
muscles  supplied  by  the  branches  which  come  off  from  the 
nerve  at  a  higher  point  than  that  irritated,  are  never  directly 
excited  to  contraction.  No  contraction,  for  instance,  is  pro- 
duced in  the  frontal  muscle  by  irritating  the  branches  of  the 
facial  nerve  that  ramify  upon  the  face ;  because  that  muscle 
derives  its  motor  nerves  from  the  trunk  of  the  facial  previous 
to  these  branches.  So,  again,  because  the  isolation  of  motor 
nerve-fibres  is  as  complete  as  that  of  sensitive  ones,  the  irrita- 
tion of  a  part  of  the  fibres  of  the  motor  nerve  does  not  affect 
the  motor  power  of  the  whole  trunk,  but  only  that  of  the  por- 
tion to  which  the  stimulus  is  applied.  And  it  is  from  the  same 
fact  that,  when  a  motor  nerve  enters  a  plexus  and  contributes 
with  other  nerves  to  the  formation  of  a  nervous  trunk  pro- 
ceeding from  the  plexus,  it  does  not  impart  motor  power  to 
the  whole  of  that  trunk,  but  only  retains  it  isolated  in  the 
fibres  which  form  its  continuation  in  the  branches  of  that 
trunk. 

Functions  of  Nerve- Centres. 

As  already  observed  (p.  375),  the  term  nerve-centre  is  applied 
to  all  those  parts  of  the  nervous  system  which  contain  gan- 
glion corpuscles,  or  vesicular  nerve-substance,  i.  e.,  the  brain, 
spinal  cord,  and  the  several  ganglia  which  belong  to  the  cere- 
bro-spinal  and  the  sympathetic  systems.  Each  of  these  nervous 


FUNCTIONS    OF     NERVE-CENTRES.  383 

centres  has  a  proper  range  of  functions,  the  extent  of  which 
bears  a  direct  proportion  to  the  number  of  nerve-fibres  that 
connect  it  with  the  various  organs  of  the  body,  and  with  other 
nervous  centres ;  but  they  all  have  certain  general  properties 
and  modes  of  action  common  to  them  as  nervous  centres. 

It  is  generally  regarded  as  the  property  of  nervous  centres 
that  they  originate  the  impulses  by  which  muscles  may  be  ex- 
cited to  action,  and  by  which  the  several  functions  of  organic 
life  may  be  maintained.  Hence,  they  are  often  called  sources 
or  originators  of  nervous  power  or  force.  But  the  instances  in 
which  these  expressions  can  be  used  are  very  few,  and,  strictly 
speaking,  do  not  exist  at  all.  The  brain  does  not  issue  any 
force,  except  when  itself  impressed  by  some  force  from  within, 
or  stimulated  by  an  impression  from  without ;  neither  without 
such  previous  impressions  do  the  other  nerve-centres  produce 
or  issue  motor  impulses.  The  intestinal  ganglia,  for  example, 
do  not  give  out  the  nervous  force  necessary  to  the  contractions 
of  the  intestines,  except  when  they  receive,  through  their  cen- 
tripetal nerves,  the  stimuli  of  substances  in  the  intestinal  canal. 
So,  also,  the  spinal  cord ;  for  a  decapitated  animal  lies  motion- 
less so  long  as  no  irritation  is  applied  to  its  centripetal  nerves, 
though  the  moment  they  are  touched  movements  ensue. 

The  more  certain  and  general  office  of  all  the  nervous  centres 
is  that  of  variously  disposing  and  transferring  the  impressions 
that  reach  them  through  the  several  centripetal  nerve-fibres. 
In  nerve-fibres,  as  already  said,  impressions  are  only  conducted 
in  the  simple  isolated  course  of  the  fibre ;  in  all  the  nervous 
centres  an  impression  may  be  not  only  conducted,  but  also 
communicated  ;  in  the  brain  alone  it  may  be  perceived. 

Conduction  in  or  through  nerve-centres  may  be  thus  simply 
illustrated.  The  food  in  a  given  portion  of  the  intestines, 
acting  as  a  stimulus,  produces  a  certain  impression  on  the 
nerves  in  the  mucous  membrane,  which  impression  is  conveyed 
through  them  to  the  adjacent  ganglia  of  the  sympathetic.  In 
ordinary  cases,  the  consequence  of  such  an  impression  of  the 
ganglia  is  the  movement  of  the  muscular  coat  of  that  and  the 
adjacent  part  of  the  canal.  But  if  irritant  substances  be 
mingled  with  the  food,  the  sharper  stimulus  produces  a  stronger 
impression,  and  this  is  conducted  through  the  nearest  ganglia 
to  others  more  and  more  distant ;  and  from  all  these,  motor 
impulses  issuing,  excite  a  wide-extended  and  more  forcible 
action  of  the  intestines.  Or  even  through  all  the  sympathetic 
ganglia,  the  impression  may  be  further  conducted  to  the  gan- 
glia of  the  spinal  nerves,  and  through  them  to  the  spinal  cord, 
whence  may  issue  motor  impulses  to  the  abdominal  and  other 
muscles,  producing  cramp.  And  yet  further,  the  same  morbid 


384  THE    NERVOUS    SYSTEM. 

impression  may  be  conducted  through  the  spinal  cord  to  the 
brain,  where  the  mind  may  perceive  it.  In  the  opposite  direc- 
tion, mental  influence  may  be  conducted  from  the  brain  through 
a  succession  of  nervous  centres — the  spinal  cord  and  ganglia, 
and  one  or  more  ganglia  of  the  sympathetic — to  produce  the 
influence  of  the  mind  on  the  digestive  and  other  organic  func- 
tions. In  short,  in  all  cases  in  which  the  mind  either  has 
cognizance  of,  or  exercises  influence  on,  the  processes  carried 
on  in  any  part  supplied  with  sympathetic  nerves,  there  must 
be  a  conduction  of  impressions  through  all  the  nervous  centres 
between  the  brain  and  that  part.  It  is  probable  that  in  this 
conduction  through  nervous  centres  the  impression  is  not  prop- 
agated through  uninterrupted  nerve-fibres,  but  is  conveyed 
through  successive  nerve-vesicles  and  connecting  nerve-fila- 
ments ;  and  in  some  instances,  and  when  the  stimulus  is  ex- 
ceedingly powerful,  the  conduction  may  be  effected  as  quickly 
as  through  continuous  nerve-fibres. 

But  instead  of,  or  as  well  as,  being  conducted,  impressions 
made  on  nervous  centres  may  be  communicated  from  the  fibres 
that  brought  them,  to  others;  and  in  this  communication  may 
be  either  transferred,  diffused,  or  reflected. 

The  transference  of  impressions  may  be  illustrated  by  the 
pain  in  the  knee,  which  is  a  common  sign  of  disease  of  the  hip. 
In  this  case  the  impression  made  by  the  disease  on  the  nerves 
of  the  hip-joint  is  conveyed  to  the  spinal  cord ;  there  it  is  trans- 
ferred to  the  central  ends  or  connections  of  the  nerve-fibres 
distributed  about  the  knee.  Through  these  the  transferred 
impression  is  conducted  to  the  brain,  and  the  mind,  referring 
the  sensation  to  the  part  from  which  it  usually  through  these 
fibres  receives  impressions,  feels  as  if  the  disease  and  the  source 
of  pain  were  in  the  knee.  At  the  same  time  that  it  is  trans- 
ferred, the  primary  impression  may  be  also  conducted ;  and  in 
this  case  the  pain  is  felt  in  both  the  hip  and  the  knee.  So,  not 
unfrequently,  if  one  touches  a  small  pimple,  that  may  be  seated 
in  the  trunk,  a  pain  will  be  felt  in  as  small  a  spot  on  the  arm, 
or  some  other  part  of  the  trunk.  And  so,  in  whatever  part  of 
the  respiratory  organs  an  irritation  may  be  seated,  the  impres- 
sion it  produces  is  transferred  to  the  nerves  of  the  larynx ;  and 
then  the  mind  perceives  the  peculiar  sensation  of  tickling  in 
the  glottis,  which  best,  or  almost  alone,  excites  the  act  of  cough- 
ing. Or,  again,  when  the  sun's  light  falls  strongly  on  the  eye, 
a  tickling  may  be  felt  in  the  nose,  exciting  sneezing.  In  all 
these  cases,  the  primary  impression  may  be  conducted  as  well 
as  transferred ;  and  in  all  it  is  transferred  to  a  certain  set  of 
nerves  which  generally  appear  to  be  in  some  purposive  rela- 
tion with  the  nerves  first  impressed. 


REFLECTION    OF     IMPRESSION.  385 

The  diffusion  or  radiation  of  impressions  is  shown  when  an 
impression  received  at  a  nervous  centre  is  diffused  to  many 
other  fibres  in  the  same  centre,  and  produces  sensations  extend- 
ing far  beyond  or  in  an  indefinite  area  around  the  part  from 
which  the  primary  impression  was  derived.  Hence,  as  in  the 
former  cases,  result  various  kinds  of  what  have  been  denomi- 
nated sympathetic  sensations.  Sometimes  such  sensations  are 
referred  to  almost  every  part  of  the  body :  as  in  the  shock  and 
tingling  of  the  skin  produced  by  some  startling  noise.  Some- 
times only  the  parts  immediately  surrounding  the  point  first 
irritated  participate  in  the  effects  of  the  irritation ;  thus,  the 
aching  of  a  tooth  may  be  accompanied  by  pain  in  the  adjoin- 
ing teeth,  and  in  all  the  surrounding  parts  of  the  face;  the  ex- 
planation of  such  a  case  being,  that  the  irritation  conveyed  to 
the  brain  by  the  nerve-fibres  of  the  diseased  tooth  is  radiated 
to  the  central  ends  of  adjoining  fibres,  and  that  the  mind  per- 
ceives this  secondary  impression  as  if  it  were  derived  from  the 
peripheral  ends  of  the  fibres.  Thus,  also,  the  pain  of  a  calculus 
in  the  ureter  is  diffused  far  and  wide. 

All  the  preceding  examples  represent  impressions  communi- 
cated from  one  sensitive  fibre  to  others  of  the  same  kind ;  or 
from  fibres  of  special  sense  to  those  of  common  sensation.  A 
similar  communication  of  impressions  from  sensitive  to  motor 
fibres,  constitutes  reflection  of  impressions,  displays  the  impor- 
tant functions  common  to  all  nervous  centres  as  reflectors,  and 
produces  reflex  movements.  In  the  extent  and  direction  of  such 
communications,  also,  phenomena  corresponding  to  those  of 
transference  and  diffusion  to  sensitive  nerves,  are  observed  in 
the  phenomena  of  reflection.  For,  as  in  transference,  the  re- 
flection may  take  place  from  a  certain  limited  set  of  sensitive 
nerves  to  a  corresponding  and  related  set  of  motor  nerves ;  as 
when  in  consequence  of  the  impression  of  light  on  the  retina, 
the  iris  contracts,  but  no  other  muscle  moves.  Or,  as  in  diffu- 
sion or  radiation,  the  reflection  may  bring  widely-extended 
muscles  into  action :  as  when  an  irritation  in  the  larynx  brings 
all  the  muscles  engaged  in  expiration  into  coincident  move- 
ment. 

It  will  be  necessary,  hereafter,  to  consider  in  detail  so  many 
of  the  instances  of  the  reflecting  power  of  the  several  nervous 
centres,  that  it  may  be  sufficient  here  to  mention  only  the 
most  general  rules  of  reflex  action  : 

1.  For  the  manifestation  of  every  reflex  muscular  action, 
three  things  are  necessary  :  (1),  one  or  more  perfect  centrip- 
etal nerve-fibres,  to  convey  an  impression ;  (2),  a  nervous 
centre  to  which  this  impression  may  be  conveyed,  and  by 


386  THE    NERVOUS    SYSTEM. 

which  it  maybe  reflected  ;  (3),  one  or  more  centrifugal  nerve- 
fibres,  upon  which  this  impression  may  be  reflected,  and  by 
which  it  may  be  conducted  to  the  contracting  tissue.  In  the 
absence  of  any  one  of  these  three  conditions,  a  proper  reflex 
movement  could  not  take  place ;  and  whenever  impressions 
made  by  external  stimuli  on  sensitive  nerves  give  rise  to  mo- 
tions, these  are  never  the  result  of  the  direct  reaction  of  the 
sensitive  and  motor  fibres  of  the  nerves  on  each  other ;  in  all 
such  cases  the  impression  is  conveyed  by  the  sensitive  fibres  to 
a  nervous  centre,  and  is  therein  communicated  to  the  motor 
fibres. 

2.  All  reflex  actions  are  essentially  involuntary,  and  may 
be  accomplished  independently  of  the  will,  though  most  of 
them  admit  of  being  modified,  controlled,  or  prevented  by  a 
voluntary  effort. 

3.  Reflex  actions  performed  in  health  have,  for  the  most 
part,  a  distinct  purpose,  and  are  adapted  to  secure  some  end 
desirable  for  the  well-being  of  the  body ;  but,  in  disease,  many 
of  them   are  irregular  and  purposeless.     As  an  illlustration 
of  the  first  point,  may  be  mentioned  movements  of  the  diges- 
tive canal,  the  respiratory  movements,  and  the  contraction  of 
the  eyelids  and  the  pupil  to  exclude  many  rays  of  light,  when 
the  retina  is  exposed  to  a  bright  glare.     These  and  all  other 
normal  reflex  acts  afford  also  examples  of  the  mode  in  which 
the   nervous  centres  combine   and    arrange   co-ordinately  the 
actions  of  the  nerve-fibres,    so  that  many  muscles  may  act 
together  for  the  common  end.     Another  instance  of  the  same 
kind  is  furnished  by  the  spasmodic  contractions  of  the  glottis 
on  the  contact  of  carbonic  acid,  or  any  foreign  substance,  with 
the  internal  substance  of  the  epiglottis  or  larynx.     Examples 
of  the  purposeless  irregular  nature  of  morbid  reflex  action  are 
seen  in   the  convulsive  movements  of    epilepsy,  and  in  the 
spasms  of  tetanus  and  hydrophobia. 

4.  Reflex  muscular  acts  are  often  more  sustained  than  those 
produced   by    the  direct  stimulus  of    muscular  nerves.      As 
Volkmann   relates,  the  irritation  of  a  muscular  organ,  or  its 
motor  nerve,  produces  contraction  lasting  only  so  long  as  the 
irritation  continues  ;  but  irritation  applied  to  a  nervous  centre 
through  one  of  its  centripetal  nerves,  may  excite  reflex  and 
harmonious  contractions,  which  last  some  time  after  the  with- 
drawal of  the  stimulus. 

CEREBROSPINAL    NERVOUS    SYSTEM. 

The  physiology  of  the  cerebro-spinal  nervous  system  in- 
cludes that  of  the  spinal  cord,  medulla  oblongata,  and  brain, 
of  the  several  nerves  given  off  from  each,  and  of  the  ganglia 


THE    CEREBRO-SPINAL     AXIS.  387 


FIG.  140. 


View  of  the  cerebro-spinal  axis  of  the  nervous  system  (after  Bourgery).  The  right 
half  of  the  cranium  and  trunk  of  the  body  has  been  removed  by  a  vertical  section; 
the  membranes  of  the  brain  and  spinal  marrow  have  also  been  removed,  and  the 
roots  and  first  part  of  the  fifth  and  ninth  cranial,  and  of  all  the  spinal  nerves  of  th'e 


388  THE    XERVOUS    SYSTEM. 

on  those  nerves.  It  will  be  convenient  to  speak  first  of  the 
spinal  cord  and  its  nerves. 

Spinal  Cord  and  its  Nerves. 

The  spinal  cord  is  a  cylindriform  column  of  nerve-substance, 
connected  above  with  the  brain  through  the  medium  of  the 
medulla  oblongata,  terminating  below,  about  the  lower  border 
of  the  first  lumbar  vertebra,  in  a  slender  filament  of  gray  or 
vesicular  substance,  thefilum  terminate,  which  lies  in  the  midst 
of  the  roots  of  many  nerves  forming  the  eauda  equina.  The 
cord  is  composed  of  fibrous  and  vesicular  nervous  substance, 
of  which  the  former  is  situated  externally,  and  constitutes  its 
chief  portion,  while  the  latter  occupies  its  central  or  axial  por- 
tion, and  is  so  arranged,  that  on  the  surface  of  a  transverse 
section  of  the  cord  it  appears  like  two  somewhat  crescentic 
masses  connected  together  by  a  narrower  portion  or  isthmus 
(Fig.  141). 

Passing  through  the  centre  of  this  isthmus  in  a  longitudinal 
direction  is  a  minute  canal,  which  is  continued  through  the 
whole  length  of  the  cord,  and  opens  above  into  the  space  at 
the  back  of  the  medulla  oblongata  and  pons  Varolii,  called 
the  fourth  ventricle.  It  is  lined  by  a  layer  of  cylindrical 
ciliated  epithelium. 

The  spinal  cord  consists  of  two  exactly  symmetrical  halves 
united  in  the  middle  line  by  a  commissure,  but  separated  an- 
teriorly and  posteriorly  by  a*  vertical  fissure ;  the  posterior  fis- 
sure being  deeper,  but  less  wide  and  distinct  than  the  anterior. 
Each  half  of  the  spinal  cord  is  marked  on  the  sides  (obscurely 
at  the  lower  part,  but  distinctly  above)  by  two  longitudinal 
furrows,  which  divide  it  into  three  portions,  columns,  or  tracts, 
an  anterior,  middle  or  lateral,  and  posterior.  From  the  groove 
between  the  anterior  and  lateral  columns  spring  the  anterior 
roots  of  the  spinal  nerves  ;  and  just  in  front  of  the  groove  be- 
tween the  lateral  and  posterior  column  arise  the  posterior 
roots  of  the  same ;  a  pair  of  roots  on  each  side  corresponding 
to  each  vertebra  (Fig.  141). 

The  fibrous  part  of  the  cord  contains  continuations  of  the 
innumerable  fibres  of  the  spinal  nerves  issuing  from  it,  or  en- 
tering it ;  but  it  is,  probably,  not  formed  of  them  exclusively ; 
nor  is  it  a  mere  trunk,  like  a  great  nerve,  through  which  they 
may  pass  to  the  brain.  It  is,  indeed,  among  the  most  difficult 

right  side,  have  been  dissected  out  and  laid  separately  on  the  wall  of  the  skull  and 
on  the  several  vertebrae  opposite  to  the  place  of  their  natural  exit  from  the  cranio- 
spinal  cavity. 


STRUCTURE    OF    THE    SPINAL    CORD. 


389 


things  in  structural  anatomy  to  determine  the  course  of  indi- 
vidual nerve-fibres,  or  even  of  fasciculi  of  fibres,  through  even 
a  short  distance  of  the  spinal  cord  ;  and  it  is  only  by  the  exam- 


Different  views  of  a  portion  of  the  spinal  cord  from  the  cervical  region,  with  the 
roots  of  the  nerves  slightly  enlarged  (from  Quain).  In  A,  the  anterior  surface  of  the 
specimen  is  shown,  the  anterior  nerve-root  of  its  right  side  being  divided;  in  B,  a 
view  of  the  right  side  is  given ;  in  c  the  upper  surface  is  shown ;  in  D,  the  nerve-roots 
and  ganglion  are  shown  from  below.  1,  the  anterior  median  fissure ;  2,  posterior 
median  fissure ;  3,  anterior  lateral  depression,  over  which  the  anterior  nerve-roots 
are  seen  to  spread ;  4,  posterior  lateral  groove,  into  which  the  posterior  roots  are  seen 
to  sink;  5,  anterior  roots  passing  the  ganglion  :  5',  in  A,  the  anterior  root  divided  ;  6, 
the  posterior  roots,  the  fibres  of  which  pass  into  the  ganglion  6' ;  7,  the  united  or 
compound  nerve;  7',  the  posterior  primary  branch,  seen  in  A  and  D  to  be  derived  in 
part  from  the  anterior  and  in  part  from  the  posterior  root. 

iuation  of  transverse  and  longitudinal  sections  through  the 
substance  of  the  cord,  such  as  those  so  successfully  made  by 
Mr.  Lockhart  Clarke,  that  we  can  obtain  anything  like  a  cor- 
rect idea  of  the  direction  taken  by  the  fibres  of  the  roots  of  the 
spinal  nerves  within  the  cord.  From  the  information  afforded 
by  such  sections  it  would  appear,  that  of  the  root-fibres  of  the 
nerve  which  enter  the  cord,  some  assume  a  transverse,  others 
a  longitudinal  direction :  the  fibres  of  the  former  pa^s  hori- 
zontally or  obliquely  into  the  substance  of  the  cord,  in  which 

33 


390  THE     NERVOUS    SYSTEM. 

many  of  them  appear  to  become  continuous  with  fibres  enter- 
ing the  cord  from  other  roots;  others  pass  into  the  columns  of 
the  cord,  while  some  perhaps  terminate  at  or  near  the  part 
which  they  enter :  of  the  fibres  of  the  second  set,  which  usually 
first  traverse  a  portion  of  the  gray  substance,  some  pass  up- 
wards, and  others,  at  least  of  the  posterior  roots,  turn  down- 
wards, but  how  far  they  proceed  in  either  direction,  or  in  what 
manner  they  terminate,  are  questions  still  undetermined.  It 
is  probable  that  of  these  latter,  many  constitute  longitudinal 
commissures,  connecting  different  segments  of  the  cord  with 
each  other ;  while  others,  probably,  pass  directly  to  the  brain. 

The  general  rule  respecting  the  size  of  different  parts  of  the 
cord  appears  to  be,  that  the  size  of  each  part  bears  a  direct 
proportion  to  the  size  and  number  of  nerve-roots  given  off  from 
itself,  and  has  but  little  relation  to  the  size  or  number  of  those 
given  off  below  it.  Thus  the  cord  is  very  large  in  the  middle 
and  lower  part  of  its  cervical  portion,  whence  arise  the  large 
nerve-roots  for  the  formation  of  the  brachial  plexuses  and  the 
supply  of  the  upper  extremities,  and  again  enlarges  at  the 
lowest  part  of  its  dorsal  portion  and  the  upper  part  of  its  lum- 
bar, at  the  origins  of  the  large  nerves,  which,  after  forming  the 
lumbar  and  sacral  plexuses,  are  distributed  to  the  lower  ex- 
tremities. The  chief  cause  of  the  greater  size  at  these  parts  of 
the  spinal  cord  is  increase  in  the  quantity  of  gray  matter ;  for 
there  seems  reason  to  believe  that  the  white  or  fibrous  part  of 
the  cord  becomes  gradually  and  progressively  larger  from  be- 
low upwards,  doubtless  from  the  addition  of  a  certain  number 
of  upward-passing  fibres  from  each  pair  of  nerves. 

It  may  be  added,  however,  that  there  is  no  sufficient  evi- 
dence for  the  supposition  that  an  uninterrupted  continuity  of 
nerve-fibres  is  essential  to  the  conduction  of  impressions  on  the 
spinal  nerves  to  and  from  the  brain :  such  impressions  may  be 
as  well  transmitted  through  the  nerve-vesicles  of  the  cord  as 
by  the  nerve-fibres;  and  the  experiments  of  Brown-Se'quard, 
again  to  be  alluded  to,  make  it  probable  that  the  gray  sub- 
stance of  the  cord  is  the  only  channel  through  which  sensitive 
impressions  are  conveyed  to  the  brain. 

The  Nerves  of  the  Spinal  Cord  consist  of  thirty-one  pairs, 
issuing  from  the  sides  of  the  whole  length  of  the  cord,  their  num- 
ber corresponding  with  the  intervertebral  foramina  through 
which  they  pass.  Each  nerve  arises  by  two  roots,  an  anterior 
and  posterior,  the  latter  being  the  larger.  The  roots  emerge 
through  separate  apertures  of  the  sheath  of  dura  mater  sur- 
rounding the  cord ;  and  directly  after  their  emergence,  where 
the  roots  He  in  the  intervertebral  foramen,  a  ganglion  is  found 


ORIGIN    OF    THE    SPINAL     NERVES.  391 

on  the  posterior  root.  The  anterior  root  lies  in  contact  with 
the  anterior  surface  of  the  ganglion,  but  none  of  its  fibres  in- 
termingle with  those  in  the  ganglion.  But  immediately  be- 
yond the  ganglion  the  two  roots  coalesce,  and  by  the  mingling 
of  their  fibres  form  a  compound  or  mixed  spinal  nerve,  which, 
after  issuing  from  the  intervertebral  canal,  divides  into  an  an- 
terior and  posterior  branch,  each  containing  fibres  from  both 
the  roots  (Fig.  141). 

According  to  Kolliker  the  posterior  root-fibres  of  the  cord 
enter  into  no  connection  with  the  nerve-corpuscles  in  the  gan- 
glion, but  pass  directly  through,  in  one  or  more  bundles,  which 
are  collected  into  a  trunk  beyond  the  ganglion,  and  then  join 
the  motor  root.  From  most,  if  not  all,  of  the  ganglionic  cor- 
puscles, one  or  two,  rarely  more,  nerve-fibres  arise  and  pass  out 
of  the  ganglion,  in  a  peripheral  direction,  in  company  with  the 
posterior  root-fibres  of  the  cord.  Each  spinal  ganglion,  there- 
fore, is  to  be  regarded  as  a  source  of  new  nerve-fibres,  which 
Kolliker  names  ganglionic  fibres.  The  destination  of  these 
fibres  is  not  yet  determined :  probably  they  pass  especially 
into  the  vascular  branches  of  the  nerves  which  they  accompany. 

The  anterior  root  of  each  spinal  nerve  arises  by  numerous 
separate  and  converging  fasciculi  from  the  anterior  column  of 
the  cord  ;  the  posterior  root  by  more  numerous  parallel  fasciculi, 
from  the  posterior  column,  or,  rather,  from  the  posterior  part 
of  the  lateral  column  ;  for  if  a  fissure  be  directed  inwards  from 
the  groove  between  the  middle  and  posterior  columns,  the  pos- 
terior roots  will  remain  attached  to  the  former.  The  anterior 
roots  of  each  spinal  nerve  consist  exclusively  of  motor  fibres ; 
the  posterior  as  exclusively  of  sensitive  fibres.  For  the  knowl- 
edge of  this  important  fact,  and  much  of  the  consequent  prog- 
ress of  the  physiology  of  the  nervous  system,  science  is  in- 
debted to  Sir  Charles  Bell.  The  fact  is  proved  in  various 
ways.  Division  of  the  anterior  roots  of  one  or  more  nerves  is 
followed  by  complete  loss  of  motion  in  the  parts  supplied  by 
the  fibres  of  such  roots ;  but  the  sensation  of  the  same  parts 
remains  perfect.  Division  of  the  posterior  roots  destroys  the 
sensibility  of  the  parts  supplied  by  their  fibres,  while  the  power 
of  motion  continues  unimpaired.  Moreover,  irritation  of  the 
ends  of  the  distal  portions  of  the  divided  anterior  roots  of  a 
nerve  excites  muscular  movements;  irritation  of  the  ends  of  the 
proximal  portions,  which  are  still  in  connection  with  the  cord, 
is  followed  by  no  effect.  Irritation  of  the  distal  portions  of 
the  divided  posterior  roots,  on  the  other  hand,  produces  ,no 
muscular  movements  and  no  manifestation  of  pain ;  for,  as  al- 
ready stated,  sensitive  nerves  convey  impressions  only  towards 
the  nervous  centres:  but  irritation  of  the  proximal  portions  of 


392  THE    NERVOUS    SYSTEM. 

these  roots  elicit  signs  of  intense  suffering.  Occasionally,  under 
this  last  irritation,  muscular  movements  also  ensue;  but  these 
are  either  voluntary,  or  the  result  of  the  irritation  being  re- 
flected from  the  sensitive  to  the  motor  fibres.  Occasionally, 
too,  irritation  of  the  distal  ends  of  divided  anterior  roots  elicits 
signs  of  pain,  as  well  as  producing  muscular  movements:  the 
pain  thus  excited  is  probably  the  result  of  cramp  (Brown-Se- 
quard). 

As  an  example  of  the  experiments  of  which  the  preceding 
paragraph  gives  a  summary  account,  this  may  be  mentioned  : 
If  in  a  frog  the  three  posterior  roots  of  the  nerves  going  to  the 
hinder  extremity  be  divided  on  the  left  side,  and  the  three  an- 
terior roots  of  the  corresponding  nerves  on  the  right  side,  the 
left  extremity  will  be  deprived  of  sensation,  the  right  of  motion. 
If  the  foot  of  the  right  leg,  which  is  still  endowed  with  sensa- 
tion but  not  with  the  power  of  motion,  be  cut  off,  the  frog  will 
give  evidence  of  feeling  pain  by  movements  of  all  parts  of  the 
body  except  the  right  leg  itself,  in  which  he  feels  the  pain.  If, 
on  the  contrary,  the  foot  of  the  left  leg,  which  has  the  power 
of  motion,  but  is  deprived  of  sensation,  is  cut  off,  the  frog  does 
not  feel  it,  and  no  movement  follows,  except  the  twitching  of 
the  muscles  irritated  by  cutting  them  or  their  tendons. 

Functions  of  the  Spinal  Cord. 

The  spinal  cord  manifests  all  the  properties  already  assigned 
to  nerve  centres  (see  p.  382). 

1.  It  is  capable  of  conducting  impressions,  or  states  of  ner- 
vous excitement.  Through  it,  the  impressions  made  upon  the 
peripheral  extremities  or  other  parts  of  the  spinal  sensitive 
nerves  are  conducted  to  the  brain,  where  alone  they  can  be 
perceived  by  the  mind.  Through  it,  also,  the  stimulus  of  the 
will,  applied  to  the  brain,  is  capable  of  exciting  the  action  of 
the  muscles  supplied  from  it  with  motor  nerves.  And  for  all 
these  conductions  of  impressions  to  and  fro  between  the  brain 
and  the  spinal  nerves,  the  perfect  state  of  the  cord  is  necessary ; 
for  when  any  part  of  it  is  destroyed,  and  its  communication 
with  the  brain  is  interrupted,  impressions  on  the  sensitive 
nerves  given  off  from  it  below  the  seat  of  injury,  cease  to  be 
propagated  to  the  brain,  and  the  mind  loses  the  power  of  vol- 
untarily exciting  the  motor  nerves  proceeding  from  the  por- 
tion of  cord  isolated  from  the  brain. 

Illustrations  of  this  are  furnished  by  various  examples  of 
paralysis,  but  by  none  better  than  by  the  common  paraplegia, 
or  loss  of  sensation  and  voluntary  motion  in  the  lower  part  of 
the  body,  in  consequence  of  destructive  disease  or  injury  of  a 


FUNCTIONS    OF    THE    SPINAL    CORD.         393 

portion,  including  the  whole  thickness,  of  the  spinal  cord. 
Such  lesions  destroy  the  communication  between  the  brain  and 
all  parts  of  the  spinal  cord  below  the  seat  of  injury,  and  con- 
sequently cut  off  from  their  connection  with  the  mind  the 
various  organs  supplied  with  nerves  issuing  from  those  parts  of 
the  cord.  But  if  this  lower  portion  of  the  cord  preserves  its 
integrity,  the  various  parts  of  the  body  supplied  with  nerves 
from  it,  though  cut  off  from  the  brain,  will  nevertheless  be  sub- 
ject to  the  influence  of  the  cord,  and,  as  presently  to  be  shown, 
will  indicate  its  other  powers  as  a  nervous  centre. 

From  what  has  been  already  said,  it  will  appear  probable 
that  the  conduction  of  impressions  along  the  cord  is  effected 
(at  least,  for  the  most  part)  through  the  gray  substance,  i.  e., 
through  the  nerve-corpuscles  and  filaments  connecting  them. 
But  there  is  reason  to  believe  that  all  parts  of  the  cord  are 
not  alike  able  to  conduct  all  impressions;  and  that,  rather,  as 
there  are  separate  nerve-fibres  for  motor  and  for  sensitive  im- 
pressions, so  in  the  cord,  separate  and  determinate  parts  serve 
to  conduct  always  the  same  kind  of  impression. 

The  important  and  philosophical  labors  of  Dr.  Brown-Sequard 
have  cast  much  new  light  on  all  relating  to  the  functions  of 
the  spinal  cord.  It  is  not  possible  to  do  justice  to  these  inves- 
tigations in  any  summary,  however  lengthy  and  complete:  the 
whole  series  (delivered  in  lectures  at  the  College  of  Surgeons) 
must  be  read  and  studied.  An  attempt  will  be  made  here  to 
point  out  only  the  principal  conclusions  deducible  from  them. 

a.  Sensitive  impressions,  conveyed  to  the  spinal  cord  by  root- 
fibres  of  the  posterior  nerves  are  not  conducted  to  the  brain  by 
the  posterior  columns  of  the  cord,  as  hitherto  has  been  gener- 
ally supposed,  but  pass  through  them  into  the  central  gray 
substance,  by  which  thev  are  transmitted  to  the  brain  (Fig. 
142). 

6.  The  impressions  thus  conveyed  to  the  gray  substance  do 
not  pass  up  to  the  brain  along  that  half  of  the  cord  correspond- 
ing to  the  side  from  which  they  have  been  received,  but,  almost 
immediately  after  entering  the  cord,  cross  over  to  the  other  side, 
and  along  it  are  transmitted  to  the  brain.  There  is  thus,  in 
the  cord  itself,  a  complete  decussation  of  sensitive  impressions 
brought  to  it;  so  that  division  or  disease  of  one  posterior  half 
of  the  cord  is  followed  by  lost  sensation,  not  in  parts  on  the 
corresponding,  but  in  those  of  the  opposite  side  of  the  body. 

c.  The  various  sensations  of  touch,  pain,  temperature,  and 
muscular  contraction,  are  probably  conducted  along  separate 
and  distinct  sets  of  fibres.  All,  however,  with  the  exception 
of  the  last  named,  undergo  decussation  in  the  spinal  cord,  and 
along  it  are  transmitted  to  the  brain  by  the  gray  matter. 


THE    NERVOUS    SYSTEM. 


d.  The  posterior  columns  of  the  cord  appear  to  have  a  great 
share  in  reflex  movements,  and  this  is  the  principal  cause  of 


The  above  diagram  (after  Brown-Sequard)  represents  the  decussation  of  the  con- 
ductors for  voluntary  movements,  and  those  for  sensation :  a,  r,  anterior  roots  and 
their  continuations  in  the  spinal  cord,  and  decussation  at  the  lower  part  of  the 
medulla  oblongata,  TO,  o;  p,  r,  the  posterior  roots  and  their  continuation  and  decus- 
sation in  the  spinal  cord  ;  g  g,  the  ganglions  of  the  roots.  The  arrows  indicate  the 
direction  of  the  nervous  action  ;  r,  the  right  side ;  I,  the  left  side.  1,  2,  3,  indicate 
places  of  alteration  in  a  lateral  half  of  the  spino-cerebral  axis,  to  show  the  influence 
on  the  two  kinds  of  conductors,  resulting  from  section  of  the  cord  at  any  one  of  these 
three  places. 

the  peculiar  kind  of  paralysis  so  often  observed  in  disease  of 
these  columns. 

e.  Impulses  of  the  will,  leading  to  voluntary  contractions  of 
muscles,  appear  to  be  transmitted  principally  along  the  anterior 
columns,  and  the  contiguous  gray  matter  of  the  cord. 

/.  Decussation  of  motor  impulses  occurs,  not  in  the  spinal 
cord,  as  is  the  case  with  sensitive  impressions,  but,  as  hitherto 
admitted,  at  the  anterior  part  of  the  medulla  oblongata.  This 
decussation,  however,  does  not  take  place,  as  generally  sup- 


CONDITION     OF    THE    SPINAL    CORD.         395 

posed,  all  along  the  median  line,  at  the  base  of  the  enceph- 
alon,  but  only  at  that  portion  of  the  anterior  pyramids,  which 
is  continuous  with  the  lateral  columns  of  the  cord.  Hence, 
the  mandates  of  the  will,  having  made  their  decussation,  first 
enter  the  cord  by  the  lateral  tracts  and  adjoining  gray  matter, 
and  then  pass  to  the  anterior  columns  and  to  the  gray  matter 
associated  with  them.  Accordingly,  division  of  the  anterior 
pyramids,  at  the  point  of  decussation,  is  followed  by  paralysis 
of  motion  in  all  parts  below ;  while  division  of  the  olivary 
bodies,  which  constitute  the  true  continuations  of  the  anterior 
columns  of  the  cord,  appears  to  produce  very  little  paralysis. 
Disease  or  division  of  any  part  of  the  cerebro-spinal  axis  above 
the  seat  of  decussation  is  followed,  as  well  known,  by  impaired 
or  lost  power  of  motion  on  the  opposite  side  of  the  body  ;  while 
a  like  injury  inflicted  below  this  part,  induces  similar  paralysis 
on  the  corresponding  side. 

2.  In  the  second  place,  the  spinal  cord  as  a  nerve-centre,  or 
rather  as  an  aggregate  of  many  nervous  centres,  has  the  power 
of  communicating  impressions  in  the  several  ways  already  men- 
tioned (p.  384). 

Examples  of  the  transference  and  radiation  of  impressions 
in  the  cord  have  been  given ;  and  that  the  transference  at 
least  takes  place  in  the  cord,  and  not  in  the  brain,  is  nearly 
proved  by  the  case  of  pain  felt  in  the  knee  and  not  in  the  hip, 
in  diseases  of  the  hip ;  of  pain  felt  in  the  urethra  or  glans 
penis,  and  not  in  the  bladder,  in  calculus ;  for,  if  both  the 
primary  and  the  secondary  or  transferred  impressions  were  in 
the  brain,  both  should  be  always  felt.  Of  radiations  of  im- 
pressions, there  are,  perhaps,  no  means  of  deciding  whether 
they  take  place  in  the  spinal  cord  or  in  the  brain ;  but  the 
analogy  of  the  cases  of  transference  makes  it  probable  that 
the  communication  is,  in  this  also,  effected  in  the  cord. 

The  power,  as  a  nerve-centre,  of  comnmicating  impressions 
from  sensitive  to  motor,  or,  more  strictly,  from  centripetal  to 
centrifugal  nerve-fibres,  is  what  is  usually  discussed  as  the 
reflex  function  of  the  spinal  cord.  Its  general  mode  of  action, 
its  general  though  incomplete  independence  of  consciousness 
and  of  the  will,  and  the  conditions  necessary  for  its  perfection, 
have  been  already  stated.  These  points,  and  the  extent  to 
which  the  power  operates  in  the  production  of  the  natural 
reflex  movements  of  the  body,  have  now  to  be  further  illustra- 
ted. They  will  be  described  in  terms  adapted  to  the  general 
rules  of  reflection  of  impressions  in  nervous  centres,  avoiding 
all  such  terms  as  might  seem  to  imply  that  the  power  of  the 
spinal  cord  in  reflecting,  is  different  in  kind  from  that  of  all 
other  nervous  centres. 


396  THE    NERVOUS    SYSTEM. 

The  occurrence  of  movements  under  the  influence  of  the 
spinal  cord,  and  independent  of  the  will,  is  well  exemplified 
in  the  acts  of  swallowing,  in  which  a  portion  of  food  carried 
by  voluntary  efforts  into  the  fauces,  is  conveyed  by  successive 
involuntary  contractions  of  the  constrictors  of  the  pharynx 
and  muscular  walls  of  the  oesophagus  into  the  stomach.  These 
contractions  are  excited  by  the  stimulus  of  the  food  on  the 
centripetal  nerves  of  the  pharynx  and  oesophagus  Being  first 
conducted  to  the  spinal  cord  and  medulla  oblongata,  and 
thence  reflected  through  the  motor  nerves  of  these  parts.  All 
these  movements  of  the  pharynx  and  oesophagus  are  involun- 
tary ;  the  will  cannot  arrest  them  or  modify  them  ;  and  though 
the  mind  has  a  certain  consciousness  of  the  food  passing,  which 
becomes  less  as  the  food  passes  further,  yet  that  this  is  not 
necessary  to  the  act  of  deglutition,  is  shown  by  its  occurring 
when  the  influence  of  the  mind  is  completely  removed ;  as 
when  food  is  introduced  into  the  fauces  or  pharynx  during  a 
state  of  complete  coma,  or  in  a  brainless  animal. 

So  also,  for  example,  under  the  influence  of  the  spinal  cord, 
the  involuntary  and  unfelt  muscular  contraction  of  the  sphinc- 
ter ani  is  maintained  when  the  mind  is  completely  inactive,  as 
in  deep  sleep,  but  ceases  when  the  lower  part  of  the  cord  is 
destroyed,  and  cannot  be  maintained  by  the  will. 

The  independence  of  the  mind  manifested  by  the  reflecting 
power  of  the  cord,  is  further  shown  in  the  perfect  occurrence 
of  the  reflex  movements  when  the  spinal  cord  and  the  brain 
are  disconnected,  as  in  decapitated  animals,  and  in  cases  of 
injuries  or  diseases  so  affecting  the  spinal  cord  as  to  divide  or 
disorganize  its  whole  thickness  at  any  part  whose  perfection 
is  not  essential  to  life.  Thus,  when  the  head  of  a  lizard  is  cut 
off,  the  trunk  remains  standing  on  the  feet,  and  the  body 
writhes  when  the  skin  is  irritated.  If  the  animal  be  cut  in 
two,  the  lower  portion  can  be  excited  to  motion  as  well  as  the 
upper  portion ;  the  tail  may  be  divided  into  several  segments, 
and  each  segment,  in  which  any  portion  of  spinal  cord  is  con- 
tained, contracts  on  the  slightest  touch ;  even  the  extremity 
of  the  tail  moves  as  before,  as  soon  as  it  is  touched.  All  the 
portions  of  the  animal  in  which  these  movements  can  be  ex- 
cited, contain  some  part  of  the  spinal  cord  ;  and  it  is  evidently 
the  cause  of  the  motions  excited  by  touching  the  surface  ;  for 
they  cannot  be  excited  in  parts  of  the  animal,  however  large, 
if  no  part  of  the  cord  is  contained  in  them.  Mechanical  irri- 
tation of  the  skin  excites  not  the  slightest  motion  in  the  leg 
when  it  is  separated  from  the  body ;  yet  the  extremity  of  the 
tail  moves  as  soon  as  it  is  touched.  The  same  power  of  the 
spinal  cord  in  reflecting  impressions  will  cause  an  eel,  or  a 


REFLEX    FUNCTION    OF    THE    SPINAL   CORD.    397 

frog,  or  any  other  cold-blooded  animal,  to  move  along  after  it 
is  deprived  of  its  head,  and  when,  however  much  the  move- 
ments may  indicate  purpose,  it  is  not  probable  that  conscious- 
ness or  will  has  any  share  in  them.  And  so,  in  the  human 
subject,  or  any  warm-blooded  animal,  when  the  cord  is  com- 
pletely divided  across,  or  so  diseased  at  some  part  that  the  in- 
fluence of  the  mind  cannot  be  conveyed  to  the  parts  below  it, 
the  irritation  of  any  part  of  the  surface  supplied  by  nerves 
given  off  from  the  cord  below  the  seat  of  injury,  is  commonly 
followed  by  spasmodic  and  irregular  reflex  movements,  even 
though  in  the  healthy  state  of  the  cord,  such  involuntary 
movements  could  not  be  excited  when  the  attention  of  the 
mind  was  directed  to  the  irritating  cause. 

In  the  fact  last  mentioned,  is  an  illustration  of  an  impor- 
tant difference  between  the  warm-blooded  and  the  lower  ani- 
mals, in  regard  to  the  reflecting  power  of  the  spinal  cord  (or 
its  homologue  in  the  Invertebrata),  and  the  share  which  it 
and  the  brain  have,  respectively,  in  determining  the  several 
natural  movements  of  the  body.  When,  for  example,  a  frog's 
head  is  cut  off,  the  limbs  remain  in,  or  assume,  a  natural  posi- 
tion ;  resume  it  when  disturbed  ;  and  when  the  abdomen  or 
back  is  irritated,  the  feet  are  moved  with  the  manifest  purpose 
of  pushing  away  the  irritation.  It  is  as  if  the  mind  of  the 
animal  were  still  engaged  in  the  acts.1  But,  in  division  of  the 
human  spinal  cord,  the  lower  extremities  fall  into  any  position 
that  their  weight  and  the  resistance  of  surrounding  objects 
combine  to  give  them ;  if  the  body  is  irritated,  they  do  not 
move  towards  the  irritation  ;  and  if  themselves  are  touched, 
the  consequent  movements  are  disorderly  and  purposeless. 
Now,  if  we  are  justified  by  analogy  in  assuming  that  the  will 
of  the  frog  cannot  act  more  than  the  will  of  man,  through  the 
spinal  cord  separated  from  the  brain,  then  it  must  be  admitted 
that  many  more  of  the  natural  and  purposive  movements  of 
the  body  can  be  performed  under  the  sole  influence  of  the  cord 
in  the  frog  than  in  man  ;  and  what  is  true  in  the  instance  of 
these  two  species,  is  generally  true  also  of  the  whole  class  of 
cold-blooded,  as  distinguished  from  warm-blooded,  animals. 
It  may  not,  indeed,  be  assumed  that  the  acts  of  standing,  leap- 
ing, and  other  movements,  which  decapitated  cold-blooded 

1  The  evident  adaptation  and  purpose  in  the  movements  of  the  cold- 
blooded animals,  have  led  some  to  think  that  they  must  be  conscious 
and  capable  of  will  without  their  brains.  But  purposive  movements 
are  no  proof  of  consciousness  or  will  in  the  creature  manifesting  them. 
The  movements  of  the  limbs  of  headless  frogs  are  not  more  purposive 
than  the  movements  of  our  own  respiratory  muscles  are  ;  in  which  we 
know  that  neither  will  nor  consciousness  is  at  all  times  concerned. 

34 


398  THE     NERVOUS    SYSTEM. 

animals  can  perform,  are  also  always,  in  the  entire  and  healthy 
state,  performed  involuntarily,  and  under  the  sole  influence  of 
the  cord ;  but  it  is  probable  that  such  acts  may  be,  and  com- 
monly are,  so  performed,  the  higher  nerve-centres  of  the  ani- 
mal having  only  the  same  kind  of  influence  in  modifying  and 
directing  them,  that  those  of  man  have  in  modifying  and  di- 
recting the  movements  of  the  respiratory  muscles. 

The  fact  that  such  movements  as  are  produced  by  irritating 
the  skin  of  the  lower  extremities  in  the  human  subject,  after 
division  or  disorganization  of  a  part  of  the  spinal  cord,  do  not 
follow  the  same  irritation  when  the  mind  is  active  and  con- 
nected with  the  cord  through  the  brain,  is,  probably,  due  to 
the  mind  ordinarily  perceiving  the  irritation  and  instantly 
controlling  the  muscles  of  the  irritated  and  other  parts ;  for, 
even  when  the  cord  is  perfect,  such  involuntary  movements 
will  often  follow  irritation,  if  it  be  applied  when  the  mind  is 
wholly  occupied.  When,  for  example,  one  is  anxiously  think- 
ing, even  slight  stimuli  will  produce  involuntary  and  reflex 
movements.  So,  also,  during  sleep,  such  reflex  movements 
may  be  observed  when  the  skin  is  touched  or  tickled;  for  ex- 
ample, when  one  touches  with  the  finger  the  palm  of  the  hand 
of  a  sleeping  child,  the  finger  is  grasped — the  impression  on 
the  skin  of  the  palm  producing  a  reflex  movement  of  the 
muscles  which  close  the  hand.  But  when  the  child  is  awake, 
no  such  effect  is  produced  by  a  similar  touch. 

On  the  whole,  it  may,  from  these  and  like  facts,  be  concluded 
that  the  proper  reflex  acts,  performed  under  the  influence  of 
the  reflecting  power  of  the  spinal  cord,  are  essentially  inde- 
pendent of  the  brain,  and  may  be  performed  perfectly  when 
the  brain  is  separated  from  the  cord  :l  that  these  include  a 
much  larger  number  of  the  natural  and  purposive  movements 
of  the  lower  animals  than  of  the  warm-blooded  animals  and 
man :  and  that  over  nearly  all  of  them  the  mind  may  exer- 
cise, through  the  brain,  some  control ;  determining,  directing, 
hindering,  or  modifying  them,  either  by  direct  action  or  by  its 
power  over  associated  muscles. 

In  this  fact,  that  the  reflex  movements  from  the  cord  may 
be  perfectly  performed  without  the  intervention  of  conscious- 
ness or  will,  yet  are  amenable  to  the  control  of  the  will,  we 
may  see  their  admirable  adaptation  to  the  well-being  of  the 
body.  Thus,  for  example,  the  respiratory  movements  may  be 
performed  while  the  mind  is,  in  other  things,  fully  occupied, 

1  Reflex  movements,  occurring  quite  independently  of  sensation, 
are  generally  called  exclto-motor ;  those  which  are  guided  or  accom- 
panied by  sensation,  but  not  to  the  extent  of  a  distinct  perception  or 
intellectual  process,  are  termed  sensor i-motor. 


REFLEX    FUNCTION   OF    THE   SPINAL    CORD.    399 

or  in  sleep  powerless;  yet  in  an  emergency,  the  mind  can 
direct  and  strengthen  them :  and  it  can  adapt  them  to  the 
several  acts  of  speech,  effort,  &c.  Being,  for  ordinary  par- 
poses,  independent  of  the  will  and  consciousness,  they  are  per- 
formed perfectly,  without  experience  or  education  of  the  mind ; 
yet  they  may  be  employed  for  other  and  extraordinary  uses 
when  the  mind  wills,  and  so  far  as  it  acquires  power  over  them. 
Being  commonly  independent  of  the  brain,  their  constant  con- 
tinuance does  not  produce  weariness ;  for  it  is  only  in  the  brain 
that  it  or  any  other  sensation  can  be  perceived. 

The  subjection  of  the  muscles  to  both  the  spinal  cord  and 
the  brain,  makes  it  difficult  to  determine  in  man  what  move- 
ments or  what  share  in  any  of  them  can  be  assigned  to  the  re- 
flecting power  of  the  cord.  The  fact  that  after  division  or 
disorganization  of  a  part  of  the  cord,  movements,  and  even 
forcible  though  purposeless  ones,  are  produced  in  the  lower 
limbs  when  the  skin  is  irritated,  proves  that  the  spinal  cord 
can  reflect  a  stimulus  to  the  action  of  the  muscles  that  are, 
naturally,  most  under  the  control  of  the  will ;  and  it  is, 
therefore,  not  improbable  that,  for  even  the  involuntary  action 
of  those  muscles,  when  the  cord  is  perfect,  it  may  supply  the 
nervous  stimulus,  and  the  will  the  direction.  As  instances  in 
which  it  supplies  both  stimulus  and  direction,  that  is,  both  ex- 
cites and  determines  the  combination  of  muscles,  may  be  men- 
tioned the  acts  of  the  abdominal  muscles  in  vomiting  and 
voiding  the  contents  of  the  bladder  and  rectum :  in  both  of 
which,  though,  after  the  period  of  infancy,  the  mind  may  have 
the  power  of  postponing  or  modifying  the  act,  there  are  all 
the  evidences  of  reflex  action ;  namely,  the  necessary  prece- 
dence of  a  stimulus,  the  independence  of  the  will,  and,  some- 
times, of  consciousness,  the  combination  of  many  muscles,  the 
perfection  of  the  act  without  the  help  of  education  or  experi- 
ence, and  its  failure  or  imperfection  in  disease  of  the  lower 
part  of  the  cord.  The  emission  of  semen  is  equally  a  reflex 
act  governed  by  the  spinal  cord ;  the  irritation  of  the  glans 
penis  conducted  to  the  spinal  cord,  and  thence  reflected,  ex- 
cites the  successive  and  co-ordinate  contractions  of  the  muscu- 
lar fibres  of  the  vasa  deferentia  and  vesiculse  seminales,  and  of 
the  accelerator  urinse  and  other  muscles  of  the  urethra ;  and  a 
forcible  expulsion  of  semen  takes  place,  over  which  the  mind 
has  little  or  no  control,  and  which,  in  cases  of  paraplegia,  may 
be  unfelt.  The  erection  of  the  penis,  also,  as  already  ex- 
plained (p.  153),  appears  to  be  in  part  the  result  of  a  reflex 
contraction  of  the  muscles  by  which  the  veins  returning  the 
blood  from  the  penis  are  compressed.  Irritation  of  the  vagina 
in  sexual  intercourse  appears  also  to  be  propagated  to  the 


400  THE    NERVOUS    SYSTEM. 

spinal  cord,  and  thence  reflected  to  the  motor  nerves  supplying 
the  Fallopian  tubes.  The  involuntary  action  of  the  uterus  in 
expelling  its  contents  during  parturition,  is  also  of  a  purely 
reflex  kind,  dependent  in  part  upon  the  spinal  cord,  though 
in  part  also  upon  the  sympathetic  system  :  its  independence  of 
the  brain  being  proved  by  cases  of  delivery  in  paraplegic 
women,  and  now  more  abundantly  shown  in  the  use  of  chloro- 
form. 

Besides  these  acts  regularly  performed  under  the  influence 
of  the  reflecting  power  of  the  spinal  cord,  others  are  manifested 
in  accidents,  such  as  the  movement  of  the  limbs  and  other 
parts  to  guard  the  body  against  the  effects  of  sudden  danger. 
When,  for  example,  a  limb  is  pricked  or  struck,  it  is  instantly 
and  involuntarily  withdrawn  from  the  instrument  of  injury ; 
and  the  same  preservative  tendency  of  the  reflex  power  of  the 
cord  is  shown  in  the  outstretched  arms  when  falling  forwards, 
and  their  reversed  position  when  falling  backwards ;  the 
action,  although  apparently  voluntary,  being  really,  in  most 
cases,  only  an  instance  of  reflex  action. 

To  these  instances  of  spinal  reflex  action,  some  add  yet 
many  more,  including  nearly  all  the  acts  which  seem  to  be 
performed  unconsciously,  such  as  those  of  walking,  running, 
writing,  and  the  like :  for  these  are  really  involuntary  acts. 
It  is  true  that  at  their  first  performances  they  are  voluntary, 
that  they  require  education  for  their  perfection,  and  are  at  all 
times  so  constantly  performed  in  obedience  to  a  mandate  of 
the  will,  that  it  is  difficult  to  believe  in  their  essentially  in- 
voluntary nature.  But  the  will  really  has  only  a  controlling 
power  over  their  performance ;  it  can  hasten  or  stay  them,  but 
it  has  little  or  nothing  to  do  with  the  actual  carrying  out  of 
the  effect.  And  this  is  proved  by  the  circumstance  that  these 
acts  can  be  performed  with  complete  mental  abstraction  :  and, 
more  than  this,  that  the  endeavor  to  carry  them  out  entirely 
by  the  exercise  of  the  will  is  not  only  not  beneficial,  but  posi- 
tively interferes  with  their  harmonious  aud  perfect  perform- 
ance. Any  one  may  convince  himself  of  this  fact  by  trying 
to  take  each  step  as  a  voluntary  act  in  walking  down  stairs, 
or  to  form  each  letter  or  word  in  writing  by  a  distinct  exercise 
of  the  will. 

These  actions,  however,  will  be  again  referred  to,  when 
treating  of  their  possible  connection  with  the  functions  of  the 
so-called  sensory  ganglia  (p.  413). 

The  phenomena  of  spinal  reflex  actions  in  man  are  much 
more  striking  and  unmixed  in  cases  of  disease.  In  some  of 
these,  the  effect  of  a  morbid  irritation,  or  a  morbid  irritability 
of  the  cord,  is  very  simple ;  as  when  the  local  irritation  of 


REFLEX    FUNCTION    OF   THE   SPINAL    CORD.     401 

sensitive  fibres,  being  propagated  to  the  spinal  cord,  excites 
merely  local  spasms, — spasms,  namely,  of  those  muscles,  the 
motor  fibres  of  which  arise  from  the  same  part  of  the  spinal 
cord  as  the  sensitive  fibres  that  are  irritated.  Of  such  a  case 
we  have  instances  in  the  involuntary  spasmodic  contraction  of 
muscles  in  the  immediate  neighborhood  of  inflamed  joints ; 
and  numerous  other  examples  of  a  like  kind  might  be  quoted. 
In  other  instances,  in  which  we  must  assume  that  the  cord 
is  morbidly  more  irritable,  i.  e.,  apt  to  issue  more  nervous 
force  than  is  proportionate  to  the  stimulus  applied  to  it,  a 
slight  impression  on  a  sensitive  nerve  produces  extensive 
reflex  movements.  This  appears  to  be  the  condition  in  teta- 
nus, in  which  a  slight  touch  on  the  skin  may  throw  the  whole 
body  into  convulsion.  A  similar  state  is  induced  by  the  in- 
troduction of  strychnia,  and,  in  frogs,  of  opium,  into  the  blood ; 
and  numerous  experiments  on  frogs  thus  made  tetanic,  have 
shown  that  the  tetanus  is  wholly  unconnected  with  the  brain, 
and  depends  on  the  state  induced  in  the  spinal  cord. 

It  may  seem  to  have  been  implied  that  the  spinal  cord,  as  a 
single  nervous  centre,  reflects  alike  from  all  parts  all  the  im- 
pressions conducted  to  it.  But  it  is  more  probable  that  it 
should  be  regarded  as  a  collection  of  nervous  centres  united  in 
a  continuous  column.  This  is  made  probable  by  the  fact  that 
segments  of  the  cord  may  act  as  distinct  nervous  centres,  and 
excite  motions  in  the  parts  supplied  with  nerves  given  off  from 
them ;  as  well  as  by  the  analogy  of  certain  cases  in  which  the 
muscular  movements  of  single  organs  are  under  the  control  of 
certain  circumscribed  portions  of  the  cord.  Thus  Volkmann 
has  shown  that  the  rhythmical  movements  of  the  anterior  pair 
of  lymphatic  hearts  in  the  frog  depend  upon  nervous  influ- 
ence derived  from  the  portion  of  spinal  cord  corresponding  to 
the  third  vertebra,  and  those  of  the  posterior  pair  on  influence 
supplied  by  the  portion  of  cord  opposite  the  eighth  vertebra. 
The  movements  of  the  heart  continue,  though  the  whole  of  the 
cord,  except  the  above  portions,  be  destroyed ;  but  on  the  in- 
stant of  destroying  either  of  these  portions,  though  all  the  rest 
of  the  cord  be  untouched,  the  movements  of  the  correspond- 
ing hearts  cease.  What  appears  to  be  thus  proved  in  regard 
to  two  portions  of  the  cord,  may  be  inferred  to  prevail  in  other 
portions  also ;  and  the  inference  is  reconcilable  with  most  of 
the  facts  known  concerning  the  physiology  and  comparative 
anatomy  of  the  cord. 

The  influence  of  the  spinal  cord  on  the  sphincter  ani  has 
been  already  mentioned  (p.  396).  It  maintains  this  muscle 


402  THE    NERVOUS    SYSTEM. 

in  permanent  contraction,  so  that,  except  in  the  act  of  defeca- 
tion, the  orifice  of  the  anus  is  always  closed.  This  influence 
of  the  cord  resembles  its  common  reflex  action  in  being  invol- 
untary, although  the  will  can  act  on  the  muscle  to  make  it 
contract  more  or  to  permit  its  dilatation,  and  in  that  the  con- 
stant action  of  the  muscle  is  not  felt,  nor  diminished  in  sleep, 
nor  productive  of  fatigue.  But  the  act  is  different  from  ordi- 
nary reflex  acts  in  being  nearly  constant.  In  this  respect  it 
resembles  that  condition  of  muscles  which  has  been  called 
tone,1  or  passive  contraction ;  in  a  state  in  which  they  always 
appear  to  be  when  not  active  in  health,  and  in  which,  though 
called  inactive,  they  appear  to  be  in  slight  contraction,  and 
certainly  are  not  relaxed,  as  they  are  long  after  death,  or 
when  the  spinal  cord  is  destroyed.  This  tone  of  all  the  mus- 
cles of  the  trunk  and  limbs  seems  to  depend  on  the  spinal 
cord,  as  the  contraction  of  the  sphincter  ani  does.  If  an  ani- 
mal be  killed  by  injury  or  removal  of  the  brain,  the  tone  of 
the  muscles  may  be  felt,  and  the  limbs  feel  firm  as  during 
sleep ;  but  if  the  spinal  cord  be  destroyed,  the  sphincter  ani 
relaxes,  and  all  the  muscles  feel  loose,  and  flabby,  and  atonic, 
and  remain  so  till  the  rigor  mortis  commences. 


THE   MEDULLA    OBLONGATA. 

Its  Structure. 

The  medulla  oblongata  is  a  mass  of  gray  and  white  nervous 
substance  partly  contained  within  the  cavity  of  the  cranium, 
forming  a  portion  of  the  cephalic  prolongation  of  the  spinal 
cord  and  connecting  it  with  the  brain.  The  gray  substance 
which  it  contains  is  situated  in  the  interior,  and  variously  di- 
vided into  masses  and  laminae  by  the  white  or  fibrous  substance 
which  is  arranged  partly  in  external  columns,  and  partly  in 
fasciculi  traversing  the  central  gray  matter.  The  medulla 
oblongata  is  larger  than  any  part  of  the  spinal  cord.  Its 
columns  are  pyriform,  enlarging  as  they  proceed  towards  the 
brain,  and  are  continuous  with  those  of  the  spinal  cord. 

Each  half  of  the  medulla,  therefore,  may  be  divided  into 
three  columns  or  tracts  of  fibres,  continuous  with  the  three 

1  This  kind  of  tone  must  be  distinguished  from  that  mere  firmness 
and  tension  which  it  is  customary  to  ascribe,  under  the  name  of  tone, 
to  all  tissues  that  feel  robust  and  not  flabby,  as  well  as  to  muscles. 
The  tone  peculiar  to  muscles  has  in  it  a  degree  of  vital  contraction  : 
that  of  other  tissues  is  only  due  to  their  being  well  nourished,  and 
therefore  compact  and  tense. 


STRUCTUBE  OF  THE  MEDULLA   OBLONGATA.    403 


tracts  of  which  each  half  of  the  spinal  cord  is  made  up.  The 
columns  are  more  prominent  than  those  of  the  spinal  cord,  and 
separated  from  each  other  by  deeper  grooves.  The  anterior, 
continuous  with  the  anterior  columns  of  the  cord,  are  called 
the  anterior  pyramids ;  the  posterior,  continuous  with  the  pos- 
terior columns  of  the  cord,  are  called  the  restiform  bodies ;  and 


FIG.  143. 


FIG.  144. 


FIG.  143. — View  of  the  anterior  surface  of  the  pons  varolii,  and  medulla  oblongata. 
a,  a,  anterior  pyramids,  b,  their  decussation  ;  c,  c,  olivary  bodies ;  d,  d,  restiform 
bodies  ;  e,  arciform  fibres  ;  /,  fibres  described  by  Solly  as  passing  from  the  anterior 
column  of  the  cord  to  the  cerebellum ;  g,  anterior  column  of  the  spinal  cord ;  h, 
lateral  column  ;  p,  pons  varolii ;  i,  its  upper  fibres  ;  5,  5,  roots  of  the  fifth  pair  of 
nerves. 

FIG.  144. — View  of  the  posterior  surface  of  the  pons  varolii,  corpora  quadrigemina, 
and  medulla  oblongata.  The  peduncles  of  the  cerebellum  are  cut  short  at  the  side. 
a,  a,  the  upper  pair  of  corpora  quadrigemina ;  b,  b,  the  lower ;/,/,  superior  peduncles 
of  the  cerebellum ;  c,  eminence  connected  with  the  nucleus  of  the  hypoglossal 
nerve ;  e,  that  of  the  glosso-pharyngeal  nerve  ;  i,  that' of  the  vagus  nerve  ;  d,  d,  resti- 
form bodies ;  p,  p,  posterior  pyramids  ;  v,  ?>,  groove  in  the  middle  of  the  fourth  ven- 
tricle, ending  below  in  the  calamus  scriptorius;  7,  7,  roots  of  the  auditory  nerves. 

the  lateral,  continuous  with  the  lateral  columns  of  the  cord,  are 
named  simply  from  their  position.  On  the  fibres  of  the  lateral 
column  of  each  side,  near  its  upper  part,  is  a  small  oval  mass, 
containing  gray  matter,  and  named  the  olivary  body ;  and  at 
the  posterior  part  of  the  restiform  column,  immediately  on 
each  side  of  the  posterior  median  groove,  a  small  tract  is 
marked  off  by  a  slight  groove  from  the  remainder  of  the  resti- 


404  THE    NERVOUS    SYSTEM. 

form  body,  and  called  the  posterior  pyramid.  The  restiform 
columns,  instead  of  remaining  parallel  with  each  other  through- 
out the  whole  of  the  medulla  oblongata,  diverge  near  its  upper 
part,  and  by  thus  diverging,  lay  open,  so  to  speak,  a  space 
called  the  fourth  ventricle,  the  floor  of  which  is  formed  by  the 
gray  matter  of  the  interior  of  the  medulla,  by  this  divergence 
exposed. 

On  separating  the  anterior  pyramids,  and  looking  into  the 
groove  between  them,  some  decussating  fibres  can  be  plainly 
seen. 

Distribution  of  the  Fibres  of  the  Medulla  Oblongata. 

The  anterior  pyramid  of  each  side,  although  mainly  com- 
posed of  continuations  of  the  fibres  of  the  anterior  columns  of 
the  spinal  cord,  receives  fibres  from  the  lateral  columns,  both 
of  its  own  and  the  opposite  side ;  the  latter  fibres  forming  al- 
most entirely  those  decussating  strands  before  mentioned,  which 
are  seen  in  the  groove  between  the  anterior  pyramids. 

Thus  composed,  the  anterior  pyramidal  fibres  proceeding 
onwards  to  the  brain  are  distributed  in  the  following  manner  : 
1.  The  greater  part  pass  on  through  the  poiis  to  the  cerebrum.1 
A  portion  of  the  fibres,  however,  running  apart  from  the  others, 
joins  some  fibres  from  the  olivary  body,  and  unites  with  them 
to  form  what  is  called  the  olivary  fasciculus  or  fillet.  2.  A 
small  tract  of  fibres  proceeds  to  the  cerebellum. 

The  lateral  column  on  each  side  of  the  medulla,  in  proceed- 
ing upwards,  divides  into  three  parts,  outer,  inner,  and  middle, 
which  are  thus  disposed  of :  1.  The  outer  fibres  go  with  the 
restiform  tract  to  the  cerebellum.  2.  The  middle  decussate 
across  the  middle  line  with  their  fellows,  and  form  a  part  of 
the  anterior  pyramid  of  the  opposite  side.  3.  The  inner  pass 
on  to  the  cerebrum  along  the  floor  of  the  fourth  ventricle,  on 
each  side,  under  the  name  of  the  fasciculus  teres. 

The  fibres  of  the  restiform  body  receive  some  small  contribu- 
tions from  both  the  lateral  and  anterior  columns  of  the  me- 

1  The  expressions  "continuous  fibres,"  and  the  like,  appear  to  be 
usually  understood  as  meaning  that  certain  primitive  nerve-fibres 
pas*  without  interruption  from  one  part  to  another.  But  such  con- 
tinuity of  primitive  fibres  through  long  distances  in  the  nervous 
centres  is  very  far  from  proved.  The  apparent  continuity  of  fasciculi 
(which  is  all  that  dissection  can  yet  trace)  is  explicable  on  the  suppo- 
sition that  many  comparatively  short  fibres  lie  parallel,  with  the  ends 
of  each  inlaid  among  many  others.  In  such  a  case,  th^re  would  be 
an  apparent  continuity  of  fibres;  just  as  there  is,  for  example,  when 
one  untwists  and  picks  out  a  long  cord  of  silk  or  wool,  in  which  each 
fibre  is  short,  and  yet  each  fasciculus  appears  to  be  continued  through 
the  whole  cord. 


FUNCTIONS  OF   THE   MEDULLA  OBLONGATA.    405 

dulla,  and  proceed  chiefly  to  the  cerebellum,  but  that  small 
part  behind,  called  posterior  pyramid,  is  continued  on  with  the 
fasciculus  teres  of  each  side  along  the  floor  of  the  fourth  ven- 
tricle to  the  cerebrum. 

As  in  structure,  so  also  in  the  general  endowments  of  their 
several  parts,  there  is,  probably,  the  closest  analogy  between 
the  medulla  oblongata  and  the  spinal  cord.  The  difference 
between  them  in  size  and  form  appears  due,  chiefly,  first,  to 
the  divergence,  enlargement,  and  decussation  of  the  several 
columns,  as  they  pass  to  be  connected  with  the  cerebellum  or 
the  cerebrum;  and,  secondly,  to  the  insertion  of  new  quantities 
of  gray  matter  in  the  olivary  bodies  and  other  parts,  in  adap- 
tation to  the  higher  office  and  wider  range  of  influence  which 
the  medulla  oblongata  as  a  nervous  centre  exercises. 

Functions  of  the  Medulla  Oblongata. 

In  its  functions  the  medulla  oblongata  differs  from  the 
spinal  cord  chiefly  in  the  importance  and  extent  of  the  actions 
that  it  governs.  Like  the  cord,  it  may  be  regarded,  first,  as 
conducting  impressions,  in  which  office  it  has  a  wider  extent 
of  function  than  any  other  part  of  the  nervous  system,  since 
it  is  obvious  that  all  impressions  passing  to  and  fro  between 
the  brain  and  the  spinal  cord  and  all  nerves  arising  below  the 
pons,  must  be  transmitted  through  it.  The  decussation  of  part 
of  the  fibres  of  the  anterior  pyramids  of  the  medulla  oblongata 
explains  the  phenomena  of  cross-paralysis,  as  it  is  termed,  i.  e., 
of  the  loss  of  motion  in  cerebral  apoplexy,  being  always  on  the 
side  opposite  to  that  on  which  the  effusion  of  blood  has  taken 
place.  Looking  only  to  the  anatomy  of  the  medulla  oblongata, 
it  was  not  possible  to  explain  why  the  loss  of  sensation  also  is 
on  the  side  opposite  the  injury  or  disease  of  the  brain ;  for 
there  is  no  evidence  of  a  decussation  of  posterior  fibres  like 
that  which  ensues  among  the  anterior  fibres  of  the  medulla 
oblongata.  But  the  discoveries  of  Brown-SSquard  have  shown 
that  the  crossing  of  sensitive  impressions  occurs  in  the  spinal 
cord  (see  p.  393). 

The  functions  of  the  medulla  oblongata  as  a  nerve-centre 
seem  to  be  more  immediately  important  to  the  maintenance  of 
life  than  those  of  any  other  part  of  the  nervous  system,  since 
from  it  alone,  or  in  chief  measure,  appears  to  be  reflected  the 
nervous  force  necessary  for  the  performance  of  respiration  and 
deglutition.  It  has  been  proved  by  repeated  experiments  on 
the  lower  animals  that  the  entire  brain  may  be  gradually  cut 
away  in  successive  pprtions,  and  yet  life  may  continue  for  a 
considerable  time,  ancj  the  respiratory  movements  be  uninter- 


406  THE    NERVOUS    SYSTEM. 

rupted.  Life  may  also  continue  when  the  spinal  cord  is  cut 
away  in  successive  portions  from  below  upwards  as  high  as  the 
point  of  origin  of  the  phrenic  nerve,  or  in  animals  without  a 
diaphragm,  such  as  birds  or  reptiles,  even  as  high  as  the  me- 
dulla oblongata.  In  Amphibia,  these  two  experiments  have 
been  combined ;  the  brain  being  all  removed  from  above,  and 
the  cord  from  below ;  and  so  long  as  the  medulla  oblongata 
was  intact,  respiration  and  life  were  maintained.  But  if,  in 
any  animal,  the  medulla  oblongata  is  wounded,  particularly  if 
it  is  wrounded  in  its  central  part,  opposite  the  origin  of  the 
pneumogastric  nerves,  the  respiratory  movements  cease,  and 
the  animal  dies  as  if  asphyxiated.  And  this  effect  ensues  even 
when  all  parts  of  the  nervous  system,  except  the  medulla  ob- 
longata, are  left  intact. 

Injury  and  disease  in  men  prove  the  same  as  these  experi- 
ments on  animals.  Numerous  instances  are  recorded  in  which 
injury  to  the  human  medulla  oblongata  has  produced  instanta- 
neous death ;  and,  indeed,  it  is  through  injury  of  it,  or  of  the  part 
of  the  cord  connecting  it  with  the  origin  of  the  phrenic  nerve, 
that  death  is  commonly  produced  in  fractures  and  diseases 
with  sudden  displacement  of  the  upper  cervical  vertebrae. 

The  centre  whence  the  nervous  force  for  the  production  of 
combined  respiratory  movements  appears  to  issue  is  in  the 
interior  of  that  part  of  the  medulla  oblongata  from  which  the 
pneumogastric  nerves  arise;  for  with  care  the  medulla  ob- 
longata may  be  divided  to  within  a  few  lines  of  this  part,  and 
its  exterior  may  be  removed  without  the  stoppage  of  respira- 
tion; but  it  immediately  ceases  when  this  part  is  invaded. 
This  is  not  because  the  integrity  of  the  pneumogastric  nerves 
is  essential  to  the  respiratory  movements ;  for  both  these  nerves 
may  be  divided  without  more  immediate  effect  than  a  retarda- 
tion of  these  movements.  The  conclusion,  therefore,  may  safely 
be,  that  this  part  of  the  medulla  oblongata  is  the  nervous 
centre  whereby  the  impulses  producing  the  respiratory  move- 
ments are  reflected. 

The  power  by  which  the  medulla  oblongata  governs  and 
combines  the  action  of  various  muscles  for  the  respiratory 
movements,  is  an  instance  of  the  power  of  reflexion,  which  it 
possesses  in  common  with  all  nervous  centres.  Its  general 
mode  of  action,  as  well  as  the  degree  to  which  the  mind  may 
take  part  in  respiration,  and  the  number  of  nerves  and  mus- 
cles which,  under  the  governance  of  the  medulla  oblongata, 
may  be  combined  in  the  forcible  respiratory  movements,  have 
been  already  briefly  described  (see  p.  184,  et  seq.).  That  which 
seems  most  peculiar  in  this  centre  of  respiratory  action  is  its 
wide  range  of  connection,  the  number  of  nerves  by  which  the 


FUNCTIONS   OF   THE    MEDULLA  OBLONGATA.    407 

centripetal  impression  to  excite  motion  may  be  conducted,  and 
the  number  and  distance  of  those  through  which  the  motor 
impulse  may  be  directed.  The  principal  centripetal  nerves 
engaged  in  respiration  are  the  pneumogastic,  whose  branches 
supplying  the  lungs  appear  to  convey  the  most  acute  impres- 
sion of  the  "  necessity  of  breathing."  When  they  are  both 
divided,  the  respiration  becomes  slower  (J.  Reid),  as  if  the 
necessity  were  less  acutely  felt :  but  it  does  not  cease,  and 
therefore  other  nerves  besides  them  must  have  the  power  of 
conducting  the  like  impression.  The  experiments  of  Volk- 
mann  make  it  probable  that  all  centripetal  nerves  possess  it 
in  some  degree,  and  that  the  existence  of  imperfectly  aerated 
blood  in  contact  with  any  of  them  acts  as  a  stimulus,  which, 
being  conveyed  to  the  medulla  oblongata,  is  reflected  to  the 
nerves  of  the  respiratory  muscles :  so  that  respiratory  move- 
ments do  not  wholly  cease  so  long  as  any  centripetal  nerves, 
and  any  nerve  supplying  muscles  of  respiration,  are  both  in 
continuous  connection  with  the  respiratory  centre  of  the 
medulla  oblongata.  The  circulation  of  imperfectly  aerated 
blood  in  the  medulla  oblongata  itself  may  also  act  as  a  stimu- 
lus, and  react  through  this  nerve-centre  on  the  nerves  which 
supply  the  inspiratory  muscles. 

The  wide  extent  of  connection  which  belongs  to  the  medulla 
oblongata  as  the  centre  of  the  respiratory  movements,  is  further 
shown  by  the  fact  that  impressions  by  mechanical  and  other 
ordinary  stimuli,  made  on  many  parts  of  the  external  or  inter- 
nal surface  of  the  body,  may  induce  respiratory  movements. 
Thus  involuntary  respirations  are  induced  by  the  sudden  con- 
tact of  cold  with  any  part  of  the  skin,  as  in  dashing  cold  water 
into  the  face.  Irritation  of  the  mucous  membrane  of  the  nose 
produces  sneezing.  Irritation  in  the  pharynx,  oesophagus,  stom- 
ach, or  intestines,  excites  the  concurrence  of  the  respiratory 
movements  to  produce  vomiting.  Violent  irritation  in  the  rec- 
tum, bladder,  or  uterus,  gives  rise  to  a  concurrent  action  of  the 
respiratory  muscles,  so  as  to  effect  the  expulsion  of  the  faeces, 
urine,  or  foetus. 

The  medulla  oblongata  appears  to  be  the  centre  whence  are 
derived  the  motor  impulses  enabling  the  muscles  of  the  palate, 
pharynx,  and  oesophagus,  to  produce  the  successive  co-ordinate 
and  adapted  movements  necessary  to  the  act  of  deglutition 
(see  p.  213).  This  is  proved  by  the  persistence  of  swallowing 
in  some  of  the  lower  animals  after  destruction  of  the  cerebral 
hemispheres  and  cerebellum ;  its  existence  in  anencephalous 
monsters ;  the  power  of  swallowing  possessed  by  marsupial 
embryos  before  the  brain  is  developed  ;  and  by  the  complete 
arrest  of  the  power  of  swallowing  when  the  medulla  oblongata 


408  THE    NERVOUS    SYSTEM. 

is  injured  in  experiments.  But  the  reflecting  power  herein 
exercised  by  the  medulla  oblongata  is  of  a  much  simpler  and 
more  restricted  kind  than  that  exercised  in  respiration ;  it  is, 
indeed,  not  more  than  a  simple  instance  of  reflex  action  by  a 
segment  of  the  spinal  axis,  receiving  impressions  for  this  pui> 
pose  from  only  a  few  centripetal  nerves,  and  reflecting  them 
to  the  motor  nerves  of  the  same  organ.  The  incident  or  cen- 
tripetal nerves  in  this  case  are  the  branches  of  the  glosso- 
pharyngeal,  and,  in  a  subordinate  degree,  those  of  the  fifth 
nerve,  some  of  the  branches  of  the  superior  laryngeal  nerve, 
which  are  distributed  to  the  pharynx ;  and  the  nerves  through 
which  the  motor  impressions  to  the  fauces  and  pharynx  are 
reflected,  are  the  pharyngeal  branches  of  the  vagus,  and,  in  sub- 
ordinate degrees,  or  as  supplying  muscles  accessory  to  the  move- 
ments of  the  pharynx,  the  branches  of  the  hypoglossal,  facial, 
cervical,  recurrent,  and  fifth  nerves.  For  the  oesophageal  move- 
ments, so  far  as  they  are  connected  with  the  medulla  oblon- 
gata, the  filaments  of  the  pneumogastric  nerve  alone,  which 
contain  both  afferent  and  efferent  fibres,  appear  to  be  sufficient 
(John  Reid). 

Though  respiration  and  life  continue  while  the  medulla 
oblongata  is  perfect  and  in  connection  with  respiratory  nerves, 
yet,  when  all  the  brain  above  it  is  removed,  there  is  no  more 
appearance  of  sensation,  or  will,  or  of  any  mental  act  in  the 
animal,  the  subject  of  the  experiment,  than  there  is  when  only 
a  spinal  cord  is  left.  The  movements  are  all  involuntary  and 
unfelt ;  and  the  medulla  oblongata  has,  therefore,  no  claim  to 
be  considered  as  an  organ  of  the  mind,  or  as  the  seat  of  sensa- 
tion or  voluntary  power.  These  are  connected  with  parts  next 
to  be  described. 

It  would  appear  that  much  of  the  reflecting  power  of  the 
medulla  oblongata  may  be  destroyed ;  and  yet  its  power  in 
the  respiratory  movements  may  remain.  Thus,  in  patients 
completely  affected  with  chloroform,  the  winking  of  the  eye- 
lids ceases,  and  irritation  of  the  pharynx  will  not  produce  the 
usual  movements  of  swallowing,  or  the  closure  of  the  glottis 
(so  that  blood  may  run  quietly  into  the  stomach,  or  even  into 
the  lungs)  ;  yet,  with  all  this,  they  may  breathe  steadily,  and 
show  that  the  power  of  the  medulla  oblougata  to  combine  in 
action  all  the  nerves  of  the  respiratory  muscles  is  perfect. 

In  addition  to  its  influence  over  the  functions  of  respiration 
and  deglutition,  the  medulla  oblongata  appears  to  be  largely 
concerned  also  in  the  faculty  of  speech. 

In  the  medulla  oblongata  appears  to  be  seated  also  the 
chief  vaso-motor  nerve-centre  (p.  452).  From  this  arise  fibres 
which,  passing  down  the  spinal  cord,  issue  with  the  anterior 


THE     PONS    VAROLII.  409 

roots  of  the  spinal  nerves,  and  enter  the  ganglia  and  branches 
of  the  sympathetic,  by  which  they  are  conducted  to  the  blood- 
vessels. 

The  influence  which  is  exercised  by  the  medulla  oblongata, 
or,  at  least,  by  its  irritation,  on  the  formation  of  sugar  in  the 
liver,  has  been  referred  to  (p.  269). 

STRUCTURE  AND  PHYSIOLOGY  OF  THE  PONS  VAROLII,  CRURA 
CEREBRI,  CORPORA  QUADRIGEMINA,  CORPORA  GENICU- 
LATA,  OPTIC  THALAMI,  AND  CORPORA  STRIATA. 

Pom  Varolii. — The  mesocephalon,  or  pons  (o,  Fig.  145),  is 
composed  principally  of  transverse  fibres  connecting  the  two 
hemispheres  of  the  cerebellum,  and  forming  its  principal  com- 
missure. But  it  includes,  interlacing  with  these,  numerous 
longitudinal  fibres  which  connect  the  medulla  oblongata  with 
the  cerebrum,  and  transverse  fibres  which  connect  it  with  the 
cerebellum.  Among  the  fasciculi  of  nerve-fibres  by  which 
these  several  parts  are  connected,  the  pons  also  contains  abun- 
dant gray  or  vesicular  substance,  which  appears  irregularly 
placed  among  the  fibres,  and  fills  up  all  the  interstices. 

The  anatomical  distribution  of  the  fibres,  both  transverse 
and  longitudinal,  of  which  the  pons  is  composed,  is  sufficient 
evidence  of  its  functions  as  a  conductor  of  impressions  from 
one  part  of  the  cerebro-spinal  axis  to  another. 

Concerning  its  functions  as  a  nerve-centre,  little  or  nothing 
is  certainly  known. 

Crura  Cerebri. — The  crura  cerebri  (I,  Fig.  145),  are  prin- 
cipally formed  of  nerve-fibres,  of  which  the  inferior  or  more 
superficial  are  continuous  with  those  of  the  anterior  py- 
ramidal tracts  of  the  medulla  oblongata,  and  the  superior  or 
deeper  fibres  with  the  lateral  and  posterior  pyramidal  tracts, 
and  with  the  olivary  fasciculus.  Besides  these  fibres  from  the 
medulla  oblongata,  are  others  from  the  cerebellum ;  and  some 
of  the  latter  as  well  as  a  part  of  the  fibres  derived  from  the 
lateral  tract  of  the  medulla  oblongata,  decussate  across  the 
middle  line. 

On  their  upper  part,  the  crura  cerebri  bear  three  pairs  of 
small  ganglia,  or  masses  of  mingled  gray  and  white  nerve- 
substance,  namely,  the  corpora  geniculata  externa  and  internet, 
and  the  corpora  quadrigemina,  or  nates  and  testes.  And  in 
their  onward  course  to  the  cerebrum,  the  fibres  of  each  crus 
cerebri  pass  through  two  large  ganglia,  the  optic  thalamus  and 
corpus  striatum,  and  in  their  substance  come  into  connection 
with  variously-shaped  masses  and  layers  of  gray  substance. 
Whether  all  the  fibres  of  the  crura  cerebri  end  in  the  gray 


410 


THE    NERVOUS    SYSTEM. 


matter  of  these  two  ganglia,  while  others  start  afresh  from 
them  to  enter  the  cerebral  hemispheres ;  or  whether  some  of 
the  fibres  of  the  crura  pass  through  them,  while  only  a  portion 


FIG.  145. 


Shows  the  under  surface  or  base  of  the  encephalon  freed  from  its  membranes— A, 
anterior,  B,  middle,  and  c,  posterior  lobe  of  cerebrum.— a.  The  fore  part  of  the  great 
longitudinal  fissure.  6.  Notch  between  hemispheres  of  the  cerebellum,  c.  Optic 
commissure,  d.  Left  peduncle  of  cerebrum,  e.  Posterior  perforated  space,  e  to  i. 
Interpeduncular  space.  //'.  Convolution  of  Sylvian  fissure,  h.  Termination  of 
gyrus  fornicatus  behind  the  Sylvian  fissure,  i.  Infundibulum.  I.  Right  middle 
crus  or  peduncle  of  cerebellum,  m  m.  Hemispheres  of  cerebellum,  n.  Corpora 
albicantia.  o.  Pons  varolii,  continuous  at  each  side  with  middle  crura  of  cerebel- 
lum, p.  Anterior  perforated  space,  q.  Horizontal  fissure  of  cerebellum,  r.  Tuber 
cinereum.  s  s'.  Sylvian  fissure,  t.  Left  peduncle  or  crus  of  cerebrum,  u  u.  Optic 
tracts,  v.  Medulla  oblougata.  x.  Marginal  convolution  of  the  longitudinal  fissure. 
1  to  9  indicate  the  several  pairs  of  cerebral  nerves,  numbered  according  to  the  usual 
notation,  viz.  1.  Olfactory  nerve.  2.  Optic.  3.  Motor  nerve  of  eye.  4.  Pathetic. 
5.  Trifacial.  6.  Abducent  nerve  of  eye.  7.  Auditory,  and  7'.  Facial.  8.  Glosso- 
pharyngeal,  8'.  Vagus,  and  8".  Spinal  accessory  nerve. 


can  be  strictly  said  to  have  their  termination  there,  must  re- 
main at  present  undecided,  the  difficulties  in  the  way  of  solv- 
ing such  an  anatomical  doubt  being  at  present  insuperable. 


CORPORA    QUADRIGEMINA.  411 

Each  cms  cerebri  contains  among  its  fibres  a  mass  of  vesic- 
ular substance,  the  locus  niger,  the  nerve-corpuscles  of  which 
abound  in  pigment-granules,  and  afford  some  of  the  best  in- 
stances of  the  caudate  structure. 

With  regard  to  their  functions,  the  crura  cerebri  may  be 
regarded  as,  principally,  conducting  organs.  As  nerve-centres 
they  are  probably  connected  with  the  functions  of  the  third 
cerebral  nerve,  which  arises  from  the  locus  niger,  and  through 
which  are  directed  the  chief  of  the  numerous  and  complicated 
movements  of  the  eyeball  and  iris. 

From  the  result  of  vivisection  it  appears  that  when  one  of 
the  crura  cerebri  is  cut  across,  the  animal  moves  round  and 
round,  rotating  around  a  vertical  axis  from  the  injured  towards 
the  sound  side.  Such  movements,  however,  attend  the  sections 
of  other  parts  than  the  crura  cerebri;  and  as  indications  of 
the  functions  of  these  parts,  the  results  of  such  experiments 
have  been  hitherto  almost  valueless. 

Corpora  Quadrigemiua. — The  corpora  quadrigemiua  (from 
which,  in  function,  the  corpora  geniculata  are  not  distinguished), 
are  the  homologues  of  the  optic  lobes  in  birds,  amphibia,  and 
fishes,  and  may  be  regarded  as  the  principal  nervous  centres 
for  the  sense  of  sight.  The  experiments  of  Flourens,  Longet, 
and  Hertwig,  show  that  removal  of  the  corpora  quadrigemina 
wholly  destroys  the  power  of  seeing ;  and  diseases  in  which 
they  are  disorganized  are  usually  accompanied  with  blindness. 
Atrophy  of  them  is  also  often  a  consequence  of  atrophy  of 
the  eyes. 

Destruction  of  one  of  the  corpora  quadrigemina  (or  of  one 
optic  lobe  in  birds),  produces  blindness  of  the  opposite  eye. 

This  loss  of  sight  is  the  only  apparent  injury  of  sensibility 
sustained  by  the  removal  of  the  corpora  quadrigemina.  The 
removal  of  one  of  them  affects  the  movements  of  the  body,  so 
that  animals  rotate,  as  after  division  of  the  crus  cerebri,  only 
more  slowly :  but  this  is  probably  due  to  giddiness  and  partial 
loss  of  sight.  The  more  evident  and  direct  influence  is  that 
produced  on  the  iris.  It  contracts  when  the  corpora  quadri- 
gemina are  irritated  :  it  is  always  dilated  when  they  are  re- 
moved :  so  that  they  may  be  regarded,  in  some  measure  at 
least,  as  the  nervous  centres  governing  its  movements,  and 
adapting  them  to  the  impressions  derived  from  the  retina 
through  the  optic  nerves  and  tracts. 

Concerning  the  functions,  taken  as  a  whole,  discharged  by 
the  olfactory  and  optic  lobes,  the  gray  substance  of  the  pons, 
the  corpora  striata  and  optic  thalami  (b,  d,  Fig.  146),  with 


412 


THE    NERVOUS    SYSTEM. 


some  other  centres  of  gray  matter  not  so  distinct,  such  as  the 
gray  matter  on  the  floor  of  the  fourth  ventricle  with  which  the 
auditory  nerve  is  connected,  the  most  philosophical  theory  is 


FIG.  146. 


Dissection  of  brain,  from  above,  exposing  the  lateral,  fourth,  and  fifth  ventricles, 
with  the  surrounding  parts  (from  Hirschfeld  and  Leveill6).  %.  a,  anterior  part,  or 
genu  of  corpus  callosum;  6,  corpus  striatum;  &',  the  corpus  striatum  of  left  side,  dis- 
sected so  as  to  expose  its  gray  substance  ;  c,  points  by  a  line  to  the  tsenia  semicircu- 
laris ;  d,  optic  thalamus;  e,  anterior  pillars  of  fornix  divided;  below  they  are  seen 
descending  in  front  of  the  third  ventricle,  and  between  them  is  seen  part  of  the  an- 
terior commissure  ;  in  front  of  the  letter  e  is  seen  the  slit-like  fifth  ventricle,  between 
the  two  laminae  of  the  septum  lucidum;  /,  soft  or  middle  commissure;  g  is  placed  in 
the  posterior  part  of  the  third  ventricle;  immediately  behind  the  latter  are  the 
posterior  commissure  (just  visible)  and  the  pineal  gland,  the  two  crura  of  which 
extend  forwards  along  the  inner  and  upper  margins  of  the  optic  thalami ;  h  and  i, 
the  corpora  quadrigemina ;  k,  superior  crus  of  cerebellum ;  close  to  k  is  the  valve  of 
Vieussens,  which  has  been  divided  so  as  to  expose  the  fourth  ventricle ;  /,  hippo- 
campus major  and  corpus  fimbriatum,  or  tsenia  hippocampi ;  m,  hippocampus  minor  ; 
n,  eminentia  collateralis  ;  o,  fourth  ventricle  ;  p,  posterior  surface  of  medulla  oblon- 
gata  ;  r,  section  of  cerebellum ;  s,  upper  part  of  left  hemisphere  of  cerebellum  exposed 
by  the  removal  of  part  of  the  posterior  cerebral  lobe. 

undoubtedly  that  which  has  been  so  ably  enunciated  by  Dr. 
Carpenter.     He  supposes  these  ganglia  to  constitute  the  real 


SENSORY    GANGLIA.  413 

sensorium  ;  that  is  to  say,  it  is  by  means  of  them  that  the 
mind  becomes  conscious  of  impressions  made  on  the  organs  or 
tissues  with  which  (by  means  of  nerve-fibres)  they  are  in  com- 
munication. Thus  impressions  made  on  the  optic  nerve,  or  its 
expansion  in  the  retina,  are  conducted  by  the  fibres  of  the 
optic  nerve  to  the  corpora  quadrigemina,  and  through  the 
medium  of  these  ganglia  the  mind  becomes  conscious  of  the 
impression  made.  And  impressions  on  the  filaments  of  the 
olfactory  or  auditory  nerve  are  in  the  same  way  perceived 
through  the  medium  of  the  olfactory  or  auditory  ganglia,  to 
which  they  are  first  conveyed.  The  optic  thalami  and  corpora 
striata  probably  have  some  function  of  a  like  kind — perhaps 
in  relation  to  ordinary  sensation,  but  nothing  is  certainly 
known  regarding  them. 

Besides  their  functions,  however,  as  media  of  communica- 
tion between  the  mind  and  external  objects,  these  sensory 
ganglia,  as  they  are  termed,  are  probably  the  nerve-centres  by 
means  of  which  those  reflex  acts  are  performed  which  require 
either  a  higher  combination  of  muscular  acts  than  can  be 
directed  by  means  of  the  medulla  oblongata  or  spinal  cord 
alone,  or,  on  the  other  hand,  such  reflex  actions  as  require  for 
their  right  performance  the  guidance  of  sensation.  Under 
this  head  are  included  various  acts,  as  walking,  reading,  writ- 
ing, and  the  like,  which  we  are  accustomed  to  consider  volun- 
tary, but  which  really  are  as  incapable  of  being  performed  by 
distinct  and  definite  acts  of  the  will  as  are  those  more  simple 
movements  of  which  we  are  not  conscious,  and  which,  per- 
formed under  the  guidance  of  the  spinal  cord  or  medulla 
oblongata  alone,  we  call  simple  reflex  actions.  It  is  true  that, 
in  the  performance  of  such  acts  as  those  just  mentioned,  a 
certain  exercise  of  the  will  is  required  at  the  commencement, 
but  that  the  carrying  out  of  its  mandates  is  essentially  reflex 
and  involuntary,  any  one  may  convince  himself  by  trying  to 
perform  each  individual  movement  concerned,  strictly  as  a 
voluntary  act. 

That  such  movements  are  reflex  and  essentially  independent 
— as  regards  their  mere  production — of  the  will,  there  is  no 
doubt ;  that  the  nerve-centres  through  which  such  reflex 
actions  are  performed  are  the  so-called  sensory  ganglia,  is,  of 
course,  only  a  theory  which  may  or  not  be  confirmed  by  future 
investigations. 

Besides  their  possible  functions  in  the  manner  just  men- 
tioned, it  is  supposed  that  these  sensory  ganglia  may  be  the 
means  of  transmitting  the  impulses  of  the  will  to  the  muscles, 
which  act  in  obedience  to  it,  and  thus  be  the  centres  of  reflex 
action  as  well  for  impressions  conveyed  downwards  to  them 

35 


414 


THE    NERVOUS    SYSTEM. 


from  the  cerebral  hemispheres,  as  for  impressions  carried  up- 
wards to  them  by  the  different  nerves  which  preserve  their 
connection  with  the  organs  of  the  various  senses. 


STRUCTURE   AND    PHYSIOLOGY    OF    THE    CEREBELLUM. 

The  cerebellum  (7,  8,  9,  10,  Fig.  147)  is  composed  of  an 
elongated  central  portion  called  the  vermiform  processes,  and 
two  hemispheres.  Each  hemisphere  is  connected  with  its  fel- 
low, not  only  by  means  of  the  vermiform  processes,  but  also 
by  a  bundle  of  fibres  called  the  middle  crus  or  peduncle  (the 
latter  forming  the  greater  part  of  the  pons  Varolii),  while  a 
superior  crus  with  the  valve  of  Vieussens,  connects  it  with  the 
cerebrum  (Fig.  147,  5),  and  an  inferior  crus  (formed  by  the 


FIG.  147. 


"*  View  of  cerebellum  in  section  and  of  fourth  ventricle,  with  the  neighboring  parts 
(from  Sappey  after  Hirschfeld  and  Leveille).  1,  median  groove  of  fourth  ventricle, 
ending  below  in  the  calamus  scriptorius,  with  the  longitudinal  eminences  formed  by 
the  fasciculi  teretes,  one  on  each  side ;  2,  the  same  groove,  at  the  place  where  the 
white  streaks  of  the  auditory  nerve  emerge  from  it  to  cross  the  floor  of  the  ventricle ; 
3,  inferior  crus  or  peduncle  of  the  cerebellum,  formed  by  the  restiform  body ;  4 , 
posterior  pyramid ;  above  this  is  the  calamus  scriptorius  ;  5,  superior  crus  of  cere- 
bellum, or  processus  a  cerebello  ad  cerebrum  (or  ad  testes) ;  6,  6,  fillet  to  the  side  of 
the  cruracerebri ;  7,  7,  lateral  grooves  of  the  crura  cerebri ;  8,  corpora  quadrigemina. 

prolonged  restiform  body)  connects  it  with  the  medulla  ob- 
longata  (3,  Fig.  147). 

The  cerebellum  is  composed  of  white  and  gray  matter  like 


FUNCTIONS    OF    THE    CEREBELLUM.          415 

that  of  the  cerebrum,  but  arranged  after  a  different  fashion,  as 
shown  in  Fig.  147. 

Besides  the  gray  substances  on  the  surface,  however,  there 
is  near  the  centre  of  the  white  substance  of  each  hemisphere, 
a  small  capsule  of  gray  matter  called  the  corpus  dentatum 
(Fig.  148,  c  d),  resembling  very  closely  the  corpus  dentatum  of 
the  olivary  body  of  the  medulla  oblongata  (Fig.  148,  o). 

The  physiology  of  the  cerebellum  may  be  considered  in  its 
relation  to  sensation,  voluntary  motion,  and  the  instincts  or 
higher  faculties  of  the  mind.  It  is  itself  insensible  to  irrita- 
tion, and  may  be  all  cut  away  without  eliciting  signs  of  pain 
(Longet).  Yet,  if  any  of  its  crura  be  touched,  pain  is  indi- 
cated ;  and,  if  the  restiform  tracts  of  the  medulla  oblongata 
be  irritated,  the  most  acute  suffering  appears  to  be  produced. 
Its  removal  or  disorganization  by  disease  is  also  generally  un- 
accompanied with  loss  or  disorder  of  sensibility  ;  animals  from 
which  it  is  removed  can  smell,  see,  hear,  and  feel  pain,  to  all 
appearance,  as  perfectly  as  before  (Flourens  ;  Magendie).  So 


FIG.  148. 


Outline  sketch  of  a  section  of  the  cerebellum  showing  the  corpus  dentatum  (from 
Quain).  %.— The  section  has  been  carried  through  the  left  lateral  part  of  the  pons, 
so  as  to  divide  the  superior  peduncle  and  pass  nearly  through  the  middle  of  the  left 
cerebellar  hemisphere.  The  olivary  body  has  also  been  divided  longitudinally  so  as 
to  expose  in  section  its  corpus  dentatum.  c  r,  crus  cerebri ;  /,  fillet ;  q,  corpora 
quadrigemina  ;  s  p,  superior  peduncle  of  the  cerebellum  divided ;  m  p,  middle  pe- 
duncle or  lateral  part  of  the  pons  Varolii,  with  fibres  passing  from  it  into  the  white 
stem ;  a  v,  continuation  of  the  white  stem  radiating  towards  the  arbor  vitse  of  the 
folia ;  c  d,  corpus  dentatum ;  o,  olivary  body  with  its  corpus  dentatum ;  p,  anterior 
pyramid. 

that,  although  the  restiform  tracts  of  the  medulla  oblongata, 
which  themselves  appear  so  sensitive,  enter  the  cerebellum,  it 
cannot  be  regarded  as  a  principal  organ  of  sensibility. 

In  reference  to  motion,  the  experiments  of  Longet  and  most 
others  agree  that  no  irritation  of  the  cerebellum  produces 
movement  of  any  kind.  Remarkable  results,  however,  are 
produced  by  removing  parts  of  its  substance.  Flourens 


416  .     THE    NERVOUS    SYSTEM. 

(whose  experiments  have  been  abundantly  confirmed  by  those 
of  Bouillaud,  Longet,  and  others)  extirpated  the  cerebellum 
in  birds  by  successive  layers.  Feebleness  and  want  of  har- 
mony of  the  movements  were  the  consequence  of  removing  the 
superficial  layers.  When  he  reached  the  middle  layers,  the 
animals  became  restless  without  being  convulsed  ;  their  move- 
ments were  violent  and  irregular,  but  their  sight  and  hearing 
were  perfect.  By  the  time  that  the  last  portion  of  the  organ 
was  cut  away,  the  animals  had  entirely  lost  the  powers  of 
springing,  flying,  walking,  standing,  and  preserving  their  equi- 
librium. When  an  animal  in  this  state  was  laid  upon  its 
back,  it  could  not  recover  its  former  posture  ;  but  it  fluttered 
its  wings,  and  did  not  lie  in  a  state  of  stupor ;  it  saw  the  blow 
that  threatened  it,  and  endeavored  to  avoid  it.  Volition,  sen- 
sation, and  memory,  therefore,  were  not  lost,  but  merely  the 
faculty  of  combining  the  actions  of  the  muscles ;  and  the  en- 
deavors of  the  animal  to  rnaintan  its  balance  were  like  those 
of  a  drunken  man. 

The  experiments  afforded  the  same  results  when  repeated 
on  all  classes  of  animals ;  and,  from  them  and  the  others  be- 
fore referred  to,  Flourens  inferred  that  the  cerebellum  belongs 
neither  to  the  sensitive  nor  the  intellectual  apparatus;  and 
that  it  is  not  the  source  of  voluntary  movements,  although  it 
belongs  to  the  motor-apparatus ;  but  is  the  organ  for  the  co- 
ordination of  the  voluntary  movements,  or  for  the  excitement 
of  the  combined  action  of  muscles. 

Such  evidence  as  can  be  obtained  from  cases  of  disease  of 
this  organ  confirms  the  view  taken  by  Flourens ;  and,  on  the 
whole,  it  gains  support  from  comparative  anatomy ;  animals 
whose  natural  movements  require  most  frequent  and  exact 
combinations  of  muscular  actions  being  those  whose  cerebella 
are  most  developed  in  proportion  to  the  spinal  cord. 

M.  Foville  holds  that  the  cerebellum  is  the  organ  of  muscu- 
lar sense,  i.  e.,  the  organ  by  which  the  mind  acquires  that 
knowledge  of  the  actual  state  and  position  of  the  muscles  which 
is  essential  to  the  exercise  of  the  will  upon  them ;  and  it  must 
be  admitted  that  all  the  facts  just  referred  to  are  as  well  ex- 
plained on  this  hypothesis  as  on  that  of  the  cerebellum  being 
the  organ  for  combining  movements.  A  harmonious  combina- 
tion of  muscular  actions  must  depend  as  much  on  the  capa- 
bility of  appreciating  the  condition  of  the  muscles  with  regard 
to  their  tension,  and  to  the  force  with  which  they  are  con- 
tracting, as  on  the  power  which  any  special  nerve-centre  may 
possess  of  exciting  them  to  contraction.  And  it  is  because 
the  power  of  such  harmonious  movement  would  be  equally 
lost,  whether  the  injury  to  the  cerebellum  involved  injury  to 


FUNCTIONS    OF    THE    CEREBELLUM.         417 

the  seat  of  muscular  sense,  or  to  the  centre  for  combining  mus- 
cular actions,  that  experiments  on  the  subject  afford  no  proof 
in  one  direction  more  than  the  other. 

Gall  was  led  to  believe,  that  the  cerebellum  is  the  organ  of 
physical  love,  or,  as  Spurzheim  called  it,  of  amativeness ;  and 
this  view  is  generally  received  by  phrenologists.  The  facts 
favoring  it  are,  first,  several  cases  in  which  atrophy  of  the 
testes  and  loss  of  sexual  passion  have  been  the  consequence  of 
blows  over  the  cerebellum,  or  wounds  of  its  substance ;  sec- 
ondly, cases  in  which  disease  of  the  cerebellum  has  been  at- 
tended with  almost  constant  erection  of  the  penis,  and  frequent 
seminal  emissions;  and  thirdly,  that  it  has  seemed  possible  to 
estimate  the  degree  of  sexual  passion  in  different  persons  by 
an  external  examination  of  the  region  of  the  cerebellum. 

The  cases  of  disease  of  the  cerebellum  do  not  prove  much ; 
for  the  same  affections  of  the  genital  organs  are  more  gener- 
ally observed  in  diseases,  and  in  experimental  irritations  of 
the  medulla  oblongata  and  upper  part  of  the  spinal  cord 
(Longet). 

The  facts  drawn  from  craniological  examination  will  receive 
the  credit  given  to  the  system  of  which  they  are  a  principal 
evidence.  But,  in  opposition  to  them,  it  must  be  stated  that 
there  has  been  a  case  of  complete  disorganization  or  absence  of 
the  cerebellum  without  loss  of  sexual  passion  (Combiette, 
Longet,  and  Cruveilhier) ;  that  the  cocks  from  whom  M. 
Flourens  removed  the  cerebellum  showed  sexual  desire,  though 
they  were  incapable  of  gratifying  it ;  and  that  among  animals 
there  is  no  proportion  observable  between  the  size  of  the  cere- 
bellum and  the  development  of  the  sexual  passion.  On  the 
contrary,  many  instances  may  be  mentioned  in  which  a  larger 
sexual  appetite  coexists  with  a  smaller  cerebellum ;  as  e.  g.y 
that  rays  and  eels,  which  are  among  the  fish  that  copulate, 
have  not  laminse  on  their  almost  rudimental  cerebella ;  and 
that  cod-fish,  which  do  not  copulate,  but  deposit  their  genera- 
tive fluids  in  the  water,  have  comparatively  well-developed 
cerebella.  Among  the  Amphibia,  the  sexual  passion  is  ap- 
parently very  strong  in  frogs  and  toads ;  yet  the  cerebellum  is 
only  a  narrow  bar  of  nervous  substance.  Among  birds  there 
is  no  enlargement  of  the  cerebellum  in  the  males  that  are  polyg- 
amous ;  the  domestic  cock's  cerebellum  is  not  larger  than  the 
hen's,  though  his  sexual  passion  must  be  estimated  at  many 
times  greater  than  hers.  Among  Mammalia  the  same  rule 
holds;  and  in  this  class  the  experiments  of  M.  Lassaigne  have 
plainly  shown  that  the  abolition  of  the  sexual  passion  by  re- 
moval of  the  testes  in  early  life  is  not  followed  by  any  diminu- 
tion of  the  cerebellum ;  for  in  mares  and  stallions  the  average 


418  THE    NERVOUS    SYSTEM. 

absolute  weight  of  the  cerebellum  is  61  grains,  and  in  geldings 
70  grains ;  and  its  proportionate  weight,  compared  with  that 
of  the  cerebrum,  is,  on  average,  as  1 :  6.59  in  mares ;  as  1 :  5.97 
in  geldings,  and  only  as  1 :  7.07  in  stallions. 

On  the  whole,  therefore,  it  appears  advisable  to  wait  for 
more  evidence  before  concluding  that  there  is  any  peculiar  and 
direct  connection  between  the  cerebellum  and  the  sexual  in- 
stinct or  sexual  passion.  From  all  that  has  been  observed,  no 
other  office  is  manifest  in  it  than  that  of  regulating  and  com- 
bining muscular  movements,  or  of  enabling  them  to  be  regu- 
lated and  combined  by  so  informing  the  mind  of  the  state  and 
position  of  the  muscles  that  the  will  may  be  definitely  and 
aptly  directed  to  them. 

The  influence  of  each  half  of  the  cerebellum  is  directed  to 
muscles  on  the  opposite  side  of  the  body ;  and  it  would  appear 
that  for  the  right  ordering  of  movements,  the  actions  of  its  two 
halves  must  be  always  mutually  balanced  and  adjusted.  For 
if  one  of  its  crura,  or  if  the  pons  on  either  side  of  the  middle 
line,  be  divided,  so  as  to  cut  off  from  the  medulla  oblongata 
and  spinal  cord  the  influence  of  one  of  the  hemispheres  of  the 
cerebellum,  strangely  disordered  movements  ensue.  The  ani- 
mals fall  down  on  the  side  opposite  to  that  on  which  the  crus 
cerebelli  has  been  divided,  and  then  roll  over  continuously  and 
repeatedly ;  the  rotation  being  always  round  the  long  axis  of 
their  bodies,  and  from  the  side  on  which  the  injury  has  been 
inflicted.1  The  rotations  sometimes  take  place  with  much  ra- 
pidity ;  as  often,  according  to  M.  Magendie,  as  sixty  times  in  a 
minute,  and  may  last  for  several  days.  Similar  movements 
have  been  observed  in  men ;  as  by  M.  Serres  in  a  man  in  whom 
there  was  apoplectic  effusion  in  the  right  crus  cerebelli ;  and  by 
M.  Belhomme  in  a  woman,  in  whom  an  exostosis  pressed  on 
the  left  crus.3  They  may,  perhaps,  be  explained  by  assuming 
that  the  division  or  injury  of  the  crus  cerebelli  produces  paral- 
ysis or  imperfect  and  disorderly  movements  of  the  opposite 
side  of  the  body ;  the  animal  falls,  and  then,  struggling  with 
the  disordered  side  on  the  ground,  and  striving  to  rise  with  the 

1  Magendie  and  Miiller,  and  others  following  them,  say  the  rotation 
is  towards  the  injured  side ;  but  Longet  and  others  more  correctly 
give  the  statement  as  in  the  text.  The  difference  has  probably  arisen 
from  using  the  words  right  and  left,  without  saying  whose  right  and 
left  are  meant,  whether  those  of  the  observer  or  those  of  the  observed. 
When,  for  example,  an  animal's  right  crus  cerebelli  is  divided,  he 
rolls  from  his  own  right  to  his  own  left,  but  from  the  left  to  the  right 
of  one  who  is  standing  in  front  of  him. 

8  See  such  cases  collected  and  recorded  by  Dr.  Paget  in  the  Ed. 
Med.  and  Surg.  Journal  for  1847. 


STRUCTURE    OF    THE    CEREBRUM.  419 

other,  pushes  itself  over;  and  so,  again  and  again,  with  the 
same  act,  rotates  itself.  Such  movements  cease  when  the  other 
crus  cerebelli  is  divided  ;  but  probably  only  because  the  paral- 
ysis of  the  body  is  thus  made  almost  complete. 

STRUCTURE  AND  PHYSIOLOGY  OF  THE  CEREBRUM. 

The  cerebrum  is  placed  in  connection  with  the  pons  and 
medulla  oblongata  by  its  two  crura  or  peduncles  (Fig.  149)  :  it 
is  connected  with  the  cerebellum,  by  the  processes  called  su- 

FlG.  149. 


Plan  in  outline  of  the  encephalon,  as  seen  from  the  right  side.  y&  (From  Quain.) 
The  parts  are  represented  as  separated  from  one  another  somewhat  more  than 
natural,  so  as  to  show  their  connections.  A,  cerebrum  ;  /,  g,  h,  its  anterior,  middle, 
and  posterior  lobes;  e,  fissure  of  Sylvius;  B,  cerebellum;  C,  pons  varolii ;  D,  me- 
dulla oblongata ;  a,  peduncles  of  the  cerebrum  ;  b,  c,  d,  superior,  middle,  and  inferior 
peduncles  of  the  cerebellum. 

perior  crura  of  the  cerebellum,  or  proeessus  a  cerebello  ad  testes, 
and  by  a  layer  of  gray  matter  called  the  valve  of  Vieussens, 
which  lies  between  these  processes,  and  extends  from  the  in- 
ferior vermiform  process  of  the  cerebellum  to  the  corpora  quad- 
rigemina  of  the  cerebrum.  These  parts,  which  thus  connect 
the  cerebrum  with  the  other  principal  divisions  of  the  cerebro- 
spinal  nervous  centre,  form  parts  of  the  walls  of  a  cavity  (the 
fourth  ventricle)  and  a  canal  (the  iter  a  tertio  ad  quartum  ven- 


420  THE    NERVOUS    SYSTEM. 

triculum),  which  are  the  continuation  of  the  canal  that  in  the 
foetus  extended  through  the  whole  length  of  the  spinal  cord 
and  brain.  They  may,  therefore,  be  regarded  as  the  contin- 
uation of  the  cerebro-spinal  axis  or  column  ;  on  which,  as  a  de- 
velopment from  the  simple  type,  the  cerebellum  is  placed;  and, 
on  the  further  continuation  of  which,  structures  both  larger 
and  more  numerous  are  raised,  to  form  the  cerebrum  (Fig.  142). 

The  cerebral  convolutions  appear  to  be  formed  of  nearly 
parallel  plates  of  fibres,  the  ends  of  which  are  turned  towards 
the  surface  of  the  brain,  and  are  overlaid  and  mingled  with 
successive  layers  of  gray  nerve-substance.  The  external  gray 
matter  is  so  arranged  in  layers,  that  a  vertical  section  of  a 
convolution,  according  to  Mr.  Lockhart  Clarke,  generally 
presents  the  appearance  of  seven  layers  of  pale  and  dark  ner- 
vous substance.  The  structure  of  the  gray  matter  is  that  which 
belongs  to  vesicular  nervous  substance  (p.  375). 

It  is  nearly  certain  that  the  cerebral  hemispheres  are  the 
organ  by  which, — 1st,  we  perceive  those  clear  and  more  im- 
pressive sensations  which  we  can  retain,  and  according  to  which 
we  can  judge ;  2dly,  by  which  are  performed  those  acts  of 
will,  each  of  which  requires  a  deliberate,  however  quick,  de- 
termination ;  3dly,  they  are  the  means  of  retaining  impressions 
of  sensible  things,  and  reproducing  them  in  subjective  sensa- 
tions and  ideas;  4thly,  they  are  the  medium  of  the  higher 
emotions  and  feelings,  and  of  the  faculties  of  judgment,  under- 
standing, memory,  reflection,  induction,  and  imagination,  and 
others  of  a  like  class. 

The  evidences  that  the  cerebral  hemispheres  have  the  func- 
tions indicated  above,  are  chiefly  these :  1.  That  any  severe 
injury  of  them,  such  as  a  general  concussion,  or  sudden  pres- 
sure by  apoplexy,  may  instantly  deprive  a  man  of  all  power 
of  manifesting  externally  any  mental  faculty.  2.  That  in  the 
same  general  proportion  as  the  higher  sensuous  mental  facul- 
ties are  developed  in  the  vertebrate  animals,  and  in  man  at 
different  ages,  the  more  is  the  size  of  the  cerebral  hemispheres 
developed  in  comparison  with  the  rest  of  the  cerebro-spinal 
system.  3.  That  no  other  part  of  the  nervous  system  bears  a 
corresponding  proportion  to  the  development  of  the  mental 
faculties.  4.  That  congenital  and  other  morbid  defects  of  the 
cerebral  hemisphere  are,  in  general,  accompanied  with  corre- 
sponding deficiency  in  the  range  or  power  of  the  intellectual 
faculties  and  the  higher  instincts. 

Respecting  the  mode  in  which  the  brain  discharges  its  func- 
tions, there  is  no  evidence  whatever.  But  it  appears  that,  for 
all  but  its  highest  intellectual  acts,  one  of  the  cerebral  hemi- 
spheres is  sufficient.  For  numerous  cases  are  recorded  in 


FUNCTIONS    OF    THE    CEREBRUM.  421 

which  no  mental  defect  was  observed,  although  one  cerebral 
hemisphere  was  so  disorganized  or  atrophied  that  it  could  not 
be  supposed  capable  of  discharging  its  functions.  The  re- 
maining hemisphere  was,  in  these  cases,  adequate  to  the  func- 
tions generally  discharged  by  both;  but  the  mind  does  not 
seem  in  any  of  these  cases  to  have  been  tested  in  very  high 
intellectual  exercises ;  so  that  it  is  not  certain  that  one  hemi- 
sphere will  suffice  for  these.  In  general,  the  mind  combines, 
as  one  sensation,  the  impressions  which  it  derives  from  one 
object,  through  both  hemispheres,  and  the  ideas  to  which  the 
two  such  impressions  give  rise  are  single. 

In  relation  to  common  sensation  and  the  effort  of  the  will, 
the  impressions  .to  and  from  the  hemispheres  of  the  brain  are 
carried  across  the  middle  line :  so  that  in  destruction  or  com- 
pression of  either  hemisphere,  whatever  effects  are  produced 
in  loss  of  sensation  or  voluntary  motion,  are  observed  on  the 
side  of  the  body  opposite  to  that  on  which  the  brain  is  injured. 

In  speaking  of  the  cerebral  hemispheres  as  the  so-called 
organs  of  the  mind,  they  have  been  regarded  as  if  they  were 
single  organs,  of  which  all  parts  are  equally  appropriate  for 
the  exercise  of  each  of  the  mental  faculties.  But  it  is  pos- 
sible that  each  faculty  has  a  special  portion  of  the  brain  ap- 
propriated to  it  as  its  proper  organ.  For  this  theory  the 
principal  evidences  are  as  follows :  1.  That  it  is  in  accordance 
with  the  physiology  of  the  other  compound  organs  or  systems 
in  the  body,  in  which  each  part  has  its  special  function ;  as, 
for  example,  of  the  digestive  system,  in  which  the  stomach, 
liver,  and  other  organs  perform  each  their  separate  share  in 
the  general  process  of  the  digestion  of  the  food.  2.  That  in 
different  individuals  the  several  mental  functions  are  mani- 
fested in  very  different  degrees.  Even  in  early  childhood, 
before  education  can  be  imagined  to  have  exercised  any  in- 
fluence on  the  mind,  children  exhibit  various  dispositions — 
each  presents  some  predominant  propensity,  or  evinces  a  sin- 
gular aptness  in  some  study  or  pursuit ;  and  it  is  a  matter  of 
daily  observation  that  every  one  has  his  peculiar  talent  or  pro- 
pensity. But  it  is  difficult  to  imagine  how  this  could  be  the 
case,  if  the  manifestation  of  each  faculty  depended  on  the 
whole  of  the  brain  :  different  conditions  of  the  whole  mass 
might  affect  the  mind  generally,  depressing  or  exalting  all  its 
functions  in  an  equal  degree,  but  could  not  permit  one  faculty 
to  be  strongly  and  another  weakly  manifested.  3.  The  plu- 
rality of  organs  in  the  brain  is  supported  by  the  phenomena 
of  some  forms  of  mental  derangement.  It  is  not  usual  for  all 
the  mental  faculties  in  an  insane  person  to  be  equally  disor- 
dered ;  it  often  happens  that  the  strength  of  some  is  increased, 

36 


422  THE    NERVOUS    SYSTEM. 

while  that  of  others  is  diminished ;  and  in  many  cases  one 
function  only  of  the  mind  is  deranged,  while  all  the  rest  are 
performed  in  a  natural  manner.  4.  The  same  opinion  is  sup- 
ported by  the  fact  that  the  several  mental  faculties  are  devel- 
oped to  their  greatest  strength  at  different  periods  of  life,  some 
being  exercised  with  great  energy  in  childhood,  others  only  in 
adult  age;  and  that,  as  their  energy  decreases  in  old  age, 
there  is  not  a  gradual  and  equal  diminution  of  power  in  all  of 
them  at  once,  but,  on  the  contrary,  a  diminution  in  one  or 
more,  while  others  retain  their  full  strength,  or  even  increase 
in  power.  5.  The  plurality  of  cerebral  organs  appears  to  be 
indicated  by  the  phenomena  of  dreams,  in  which  only  a  part 
of  the  mental  faculties  are  at  rest  or  asleep,  while  the  others 
are  awake,  and,  it  is  presumed,  are  exercised  through  the  me- 
dium of  the  parts  of  the  brain  appropriated  to  them. 

These  facts  have  been  so  illustrated  and  adapted  by  phren- 
ologists, that  the  theory  of  the  plurality  of  organs  in  the  cere- 
brum, thus  made  probable,  has  been  commonly  regarded  as 
peculiar  to  phrenology,  and  as  so  essentially  connected  with  it, 
that  if  the  system  of  Gall  and  Spurzheim  be  untrue,  this 
theory  cannot  be  maintained.  But  it  is  plain  that  all  the 
system  of  phrenology  built  upon  the  theory  may  be  false,  and 
the  theory  itself  true ;  for  phrenologists  assume  not  only  this 
theory,  but  also  that  they  have  determined  all  the  primitive 
faculties,  of  which  the  mind  consists,  i.  e.,  all  the  faculties  to 
which  special  organs  must  be  assigned,  and  the  places  of  all 
those  organs  in  the  cerebral  hemispheres  and  the  cerebellum. 
That  this  is  a  system  of  error  there  need  be  no  doubt,  but  it 
is  possibly  founded  on  a  true  theory :  the  cerebrum  may  have 
many  organs,  and  the  mind  as  many  faculties ;  but  what  are 
the  faculties  that  require  separate  organs,  and  where  those 
organs  are  situate,  are  subjects  of  which  only  the  most  general 
and  rudimentary  knowledge  has  been  yet  attained. 

From  the  apparently  greater  frequency  of  interference  with 
the  faculty  of  speech  in  disease  of  the  left  than  of  the  right  half 
of  the  cerebrum,  it  has  been  thought  that  the  nerve-centre  for 
language,  including  in  this  term  all  intellectual  expression  of 
ideas,  is  situated  in  the  left  cerebral  hemisphere.  It  cannot 
be  said,  however,  that  the  existing  evidence  for  this  theory  is 
at  present  sufficient  to  have  established  it. 

Of  the  physiology  of  the  other  parts  of  the  brain,  little  or 
nothing  can  be  said. 

Of  the  offices  of  the  corpus  callosum,  or  great  transverse  and 
oblique  commissure  of  the  brain,  nothing  positive  is  known. 
But  instances  in  which  it  was  absent,  or  very  deficient,  either 
without  any  evident  mental  defect,  or  with  only  such  as  might 


THE     CORPUS    CALLOSUM. 


423 


be  ascribed  to  coincident  affections  of  other  parts,  make  it 
probable  that  the  office  which  is  commonly  assigned  to  it,  of 
enabling  the  two  sides  of  the  brain  to  act  in  concord,  is  exer- 
cised only  in  the  highest  acts  of  which  the  mind  is  capable. 
And  this  view  is  confirmed  by  the  very  late  period  of  its  de- 
velopment, and  by  its  absence  in  all  but  the  placental  Mam- 
malia.1 


FIG.  150. 


View  of  the  corpus  callosum  from  above  (from  Sappey  after  Foville).  ^.— The 
upper  surface  of  the  corpus  callosum  has  been  fully  exposed  by  separating  the  cere- 
bral hemispheres  and  throwing  them  to  the  side ;  the  gyms  fornicatus  has  been 
detached,  and  the  transverse  fibres  of  the  corpus  callosum  traced  for  some  distance 
into  the  cerebral  medullary  substance.  1,  the  upper  surface  of  the  corpus  callosum ; 
2,  median  furrow"  or  raphe ;  3,  longitudinal  striae  bounding  the  furrow  ;  4,  swelling 
formed  by  the  transverse  bands  as  they  pass  into  the  cerebrum  ;  5,  anterior  extrem- 
ity or  knee  of  the  corpus  callosum ;  8,  posterior  extremity  ;  7,  anterior,  and,  8,  pos- 
terior part  of  the  mass  of  fibres  proceeding  from  the  corpus  callosum  ;  9,  margin  of 
the  swelling ;  10,  anterior  part  of  the  convolution  of  the  corpus  callosum ;  11,  hem  or 
band  of  union  of  this  convolution;  12,  internal  convolutions  of  the  parietal  lobe; 
13,  upper  surface  of  the  cerebellum. 


1  See  oases  of  congenital  deficiency  of  the  corpus  callosum,  by  Mr. 
Paget  and  Mr.  Henry,  in  the  twenty-ninth  and  thirty-first  volumes  of 
the  Medico-Chirurgical  Transactions. 


424  THE    NERVOUS    SYSTEM. 

To  the  fornix  and  other  commissures  no  special  function  can 
be  assigned ;  but  it  is  a  reasonable  hypothesis  that  they  con- 
nect the  action  of  the  parts  between  which  they  are  severally 
placed. 

As  little  is  known  of  the  function  of  the  pineal  and  pitu- 
itary glands.  The  latter  has  been  supposed,  from  its  micro- 
scopic structure,  to  be  rather  a  ductless  gland  (p.  325)  than  a 
nervous  organ. 


PHYSIOLOGY    OF   THE    CEREBRAL   AND   SPINAL    NERVES. 

The  cerebral  nerves  are  commonly  enumerated  as  nine  pairs ; 
but  the  number  is  in  reality  twelve,  the  seventh  nerve  consist- 
ing, as  it  does,  of  two  nerves,  and  the  eighth  of  three.  These 
and  the  spinal  nerves,  of  which  there  are  thirty-one  pairs, 
symmetrically  arranged  on  each  side  of  what,  reduced  to  its 
simplest  form,  may  be  regarded  as  a  column  or  axis  of  nervous 
matter,  extending  from  the  olfactory  bulbs  on  the  ethmoid 
bone  to  the  filum  terminate  of  the  spinal  cord  in  the  lumbar 
and  sacral  portions  of  the  vertebral  canal.  The  spinal  nerves 
all  present  certain  characters  in  common,  such  as  their  double 
roots ;  the  isolation  of  the  fibres  of  sensation  in  the  posterior 
roots,  and  those  of  motion  in  the  anterior  roots ;  the  formation 
of  the  ganglia  on  the  posterior  root ;  and  the  subsequent  min- 
gling of  the  fibres  in  trunks  and  branches  of  mixed  functions. 
Similar  characters  probably  belong  essentially  to  the  cerebral 
nerves  ;  but  even  when  one  includes  the  nerves  of  special  sense, 
it  is  not  possible  to  discern  a  conformity  of  arrangement  in 
any  besides  the  fifth,  or  trifacial,  which,  from  its  many  anal- 
ogies to  the  spinal  nerves,  Sir  Charles  Bell  designated  as  a 
spinal  nerve  of  the  head. 

According  to  their  several  functions,  the  cerebral  or  cranial 
nerves  may  be  thus  arranged: 

Nerves  of  special  sense,  .  .  Olfactory,  optic,  auditory,  part  of  the 

glosso-pharyngeal,  and  the  lingual 
branch  of  the  fifth. 

Nerves  of  common  sensation,  Tho  greater  portion  of  the  fifth,  and 

part  of  the  glosso-pharyngeal. 

Nerves  of  motion,  ....  Third,  fourth,  lesser  division  of  the 

fifth,  sixth,  facial,  and  hypoglossal. 

Mixed  nerves, Pneumogastric  and  accessory. 

The  physiology  of  the  several  nerves  of  the  special  senses 
will  be  considered  with  the  organs  of  those  senses. 


THE    CEREBRAL    NERVES.  425 


Physiology  of  the  Third,  Fourth,  and  Sixth  Cerebral  or  Cranial 

Nerves. 

The  physiology  of  these  nerves  may  be  in  some  degree  com- 
bined, because  of  their  intimate  connection  with  each  other  in 
the  actions  of  the  muscles  of  the  eyeball,  which  they  supply. 
They  are  probably  all  formed  exclusively  of  motor  fibres : 
some  pain  is  indicated  when  the  trunk  of  the  third  nerve  is  ir- 
ritated near  its  origin  ;  but  this  may  be  because  of  some  fila- 
ments of  the  fifth  nerve  running  backwards  to  the  brain  in  .the 
trunk  of  the  third,  or  because  adjacent  sensitive  parts  are  in- 
volved in  the  irritation. 

The  third  nerve,  or  motor  oculi,  supplies  the  levator  palpe- 
brse  superioris  muscle,  and,  of  the  muscles  of  the  eyeball,  all 
but  the  superior  oblique  or  trochlearis,  to  which  the  fourth 
nerve  is  appropriated,  and  the  rectus  externus,  which  receives 
the  sixth  nerve.  Through  the  medium  of  the  ophthalmic  or 
lenticular  ganglion,  of  which  it  forms  what  is  called  the  short 
root,  it  also  supplies  the  motor  filaments  to  the  iris. 

When  the  third  nerve  is  irritated  within  the  skull,  all  those 
muscles  to  which  it  is  distributed  are  convulsed.  When  it  is 
paralyzed  or  divided,  the  following  effects  ensue :  first,  the 
upper  eyelid  can  be  no  longer  raised  by  the  levator  palpebrse, 
but  drops  and  remains  gently  closed  over  the  eye,  under  the 
unbalanced  influence  of  the  orbicularis  palpebrarum,  which  is 
supplied  by  the  facial  nerve :  secondly,  the  eye  is  turned  out- 
wards by  the  unbalanced  action  of  the  rectus  externus,  to 
which  the  sixth  nerve  is  appropriated :  and  hence,  from  the 
irregularity  of  the  axes  of  the  eyes,  double-sight  is  often  ex- 
perienced when  a  single  object  is  within  view  of  both  the  eyes  : 
thirdly,  the  eye  cannot  be  moved  either  upwards,  downwards, 
or  inwards ;  fourthly,  the  pupil  is  dilated. 

The  relation  of  the  third  nerve  to  the  iris  is  of  peculiar  in- 
terest. In  ordinary  circumstances  the  contraction  of  the  iris 
is  a  reflex  action,  which  may  be  explained  as  produced  by  the 
stimulus  of  light  on  the  retina  being  conveyed  by  the  optic 
nerve  to  the  brain  (probably  to  the  corpora  quadrigemina), 
and  thence  reflected  through  the  third  nerve  to  the  iris. 
Hence  the  iris  ceases  to  act  when  either  the  optic  or  the  third 
nerve  is  divided  or  destroyed,  or  when  the  corpora  quadri- 
gemina are  destroyed  or  much  compressed.  But  when  the  optic 
nerve  is  divided,  the  contraction  of  the  iris  may  be  excited  by 
irritating  that  portion  of  the  nerve  which  is  connected  with 
the  brain ;  and  when  the  third  nerve  is  divided,  the  irritation 
of  its  distal  portion  will  still  excite  contraction  of  the  iris,  in 
which  its  fibres  are  distributed. 


426  THE    NERVOUS    SYSTEM. 

The  contraction  of  the  iris  thus  shows  all  the  character  of  a 
reflex  act,  and  in  ordinary  cases  requires  the  concurrent  ac- 
tion of  the  optic  nerve,  corpora  quadrigemina,  and  third  nerve ; 
and,  probably  also,  considering  the  peculiarities  of  its  perfect 
mode  of  action,  the  ophthalmic  ganglion.  But,  besides,  both 
irides  will  contract  their  pupils  under  the  reflected  stimulus  of 
light  falling  only  on  one  retina  or  under  irritation  of  one  optic 
nerve.  Thus,  in  amaurosis  of  one  eye,  its  pupil  may  contract 
when  the  other  eye  is  exposed  to  a  stronger  light :  and  gener- 
ally the  contraction  of  each  of  the  pupils  appears  to  be  in  di- 
rect proportion  to  the  total  quantity  of  light  which  stimulates 
either  one  or  both  retinae,  according  as  one  or  both  eyes  are 
open. 

The  iris  acts  also  in  association  with  certain  other  muscles 
supplied  by  the  third  nerve:  thus,  when  the  eye  is  directed 
inwards,  or  upwards  and  inwards,  by  the  action  of  the  third 
nerve  distributed  in  the  rectus  internus  and  rectus  superior, 
the  iris  contracts,  as  if  under  direct  voluntary  influence.  The 
will  cannot,  however,  act  on  the  iris  alone  through  the  third 
nerve ;  but  this  aptness  to  contract  in  association  with  the 
other  muscles  supplied  by  the  third,  may  be  sufficient  to  make 
it  act  even  in  total  blindness  and  insensibility  of  the  retina, 
whenever  these  muscles  are  contracted.  The  contraction  of 
the  pupils,  when  the  eyes  are  moved  inwards,  as  in  looking  at 
a  near  object,  has  probably  the  purpose  of  excluding  those 
outermost  rays  of  light  which  would  be  too  far  divergent  to  be 
refracted  to  a  clear  image  on  the  retina ;  and  the  dilatation  in 
looking  straight  forwards,  as  in  looking  at  a  distant  object,  per- 
mits the  admission  of  the  largest  number  of  rays,  of  which 
none  are  too  divergent  to  be  so  refracted. 

The  fourth  nerve,  or  Nervus  trochlearis  or  patheticus,  is  ex- 
clusively motor,  and  supplies  only  the  trochlearis  or  obliquus 
superior  muscle  of  the  eyeball. 

The  sixth  nerve,  Nervus  abducens  or  ocularis  extermis  is  also, 
like  the  fourth,  exclusively  motor,  and  supplies  only  the  rectus 
extern  us  muscle.1  The  rectus  externus  is,  therefore,  convulsed, 
and  the  eye  is  turned  outwards,  when  the  sixth  nerve  is  irri- 
tated ;  and  the  muscle  paralyzed  when  the  nerve  is  disorganized, 
compressed,  or  divided.  In  all  such  cases  of  paralysis,  the  eye 
squints  inwards,  and  cannot  be  moved  outwards. 

1  In  several  animals  it  sends  filaments  to  the  iris  (Radctyffe  Hall)  ; 
and  it  has  probably  done  so  in  man,  in  some  instances  in  which  the 
iris  has  not  been  paralyzed,  while  all  the  other  parts  supplied  by  the 
third  nerve  were  (Grant). 


THE    CEREBRAL     NERVES.  427 

In  its  course  through  the  cavernous  sinus,  the  sixth  nerve 
forms  larger  communications  with  the  sympathetic  nerve  than 
any  other  nerve  within  the  cavity  of  the  skull  does.  But  the 
import  of  these  communications  with  the  sympathetic,  and  the 
subsequent  distribution  of  its  filaments  after  joining  the  sixth 
nerve,  are  quite  unknown;  and  there  is  no  reason  to  believe 
that  the  sixth  nerve  is,  in  function,  more  closely  connected  with 
the  sympathetic  than  any  other  cerebral  nerve  is. 

The  question  has  often  suggested  itself  why  the  six  muscles 
of  the  eyeball  should  be  supplied  by  three  motor  nerves  when 
all  of  them  are  within  reach  of  the  branches  of  one  nerve;  and 
the  true  explanation  would  have  more  interest  than  attaches 
to  the  movements  of  the  eye  alone;  since  it  is  probable  that 
we  have,  in  this  instance,  within  a  small  space,  an  example  of 
some  general  rule  according  to  which  associate  or  antagonist 
muscles  are  supplied  with  motor  nerves. 

Now,  in  the  several  movements  of  the  eyes,  we  sometimes 
have  to  act  with  symmetrically  placed  muscles,  as  when  both 
eyes  are  turned  upwards  or  downwards,  inwards  or  outwards.1 
All  the  symmetrically  placed  muscles  are  supplied  with  sym- 
metrical nerves,  i.  e.,  with  corresponding  branches  of  the  same 
nerves  on  the  two  sides;  and  the  action  of  these  symmetrical 
muscles  is  easy  and  natural,  as  we  have  a  natural  tendency  to 
symmetrical  movement  in  most  parts.  But  because  of  this 
tendency  to  symmetrical  movements  of  muscles  supplied  by 
symmetrical  nerves,  it  would  appear  as  if,  when  the  two  eyes 
are  to  be  moved  otherwise  than  symmetrically,  the  muscles  to 
effect  such  a  movement  must  be  supplied  with  different  nerves. 
So,  when  the  two  eyes  are  to  be  turned  towards  one  side,  say 
the  right,  by  the  action  of  the  rectus  extern  us  of  the  right  eye 
and  the  rectus  internus  of  the  left,  it  appears  as  if  the  tendency 
to  action  through  the  similar  branches  of  corresponding  nerves 
(which  would  move  both  eyes  inwards  or  outwards)  were  cor- 
rected by  one  of  these  muscles  being  supplied  by  the  sixth,  and 
the  other  by  the  third  nerve.  So  with  the  oblique  muscles : 
the  simplest  and  easiest  actions  would  be  through  branches  of 
the  corresponding  nerves,  acting  similarly  as  symmetrical 
muscles ;  but  the  necessary  movements  of  the  two  eyes  require 
the  contraction  of  the  superior  oblique  of  one  side,  to  be  asso- 
ciated with  the  contraction  of  the  inferior  oblique,  and  the  re- 
laxation of  the  superior  oblique,  of  the  opposite  side.  For  this, 
the  fourth  nerve  of  one  side  is  made  to  act  with  a  branch  of 

1  It  is  sometimes  said  that  the  external  reeti  cannot  be  put  in  action 
simultaneously:  yet  they  are  so  when  the  eyes,  having  been  both  di- 
rected inwards,  are  restored  to  the  position  which  they  have  in  looking 
straight  forwards. 


428  THE    NERVOUS    SYSTEM. 

the  third  nerve  of  the  other;  as  if  thus  the  tendency  to  simul- 
taneous action  through  the  similar  nerves  of  the  two  sides  were 
prevented.  At  any  rate,  the  rule  of  distribution  of  nerves 
here  seems  to  be,  that  when  in  frequent  and  necessary  move- 
ments any  muscle  has  to  act  with  the  antagonist  of  its  fellow 
on  the  opposite  side,  it  and  its  fellow's  antagonist  are  supplied 
from  different  nerves. 

Physiology  of  the  Fifth  or  Trigeminal  Nerve. 

The  fifth  or  trigeininal  nerve  resembles,  as  already  stated, 
the  spinal  nerves,  in  that  its  branches  are  derived  through 
two  roots ;  namely,  the  larger  or  sensitive,  in  connection  with 
which  is  the  Gasserian  ganglion,  and  the  smaller  or  motor 
root,  which  has  no  ganglion,  and  which  passes  under  the  gan- 
glion of  the  sensitive  root  to  join  the  third  branch  or  division 
which  issues  from  it.  The  first  and  second  divisions  of  the 
nerve,  which  arise  wholly  from  the  larger  root,  are  purely 
sensitive.  The  third  division  being  joined,  as  before  said,  by 
the  motor  root  of  the  nerve,  is  of  course  both  motor  and  sen- 
sitive. 

Through  the  branches  of  the  greater  or  ganglionic  portion 
of  the  fifth  nerve,  all  the  anterior  and  antero-lateral  parts  of 
the  face  and  head,  with  the  exception  of  the  skin  of  the  parotid 
region  (which  derives  branches  from  the  cervical  spinal  nerves), 
acquire  common  sensibility ;  and  among  these  parts  may  be  in- 
cluded the  organs  of  special  sense,  from  which  common  sensa- 
tions are  conveyed  through  the  fifth  nerve,  and  their  peculiar 
sensation  through  their  several  nerves  of  special  sense.  The 
muscles,  also,  of  the  face  and  lower  jaw  acquire  muscular  sen- 
sibility through  the  filaments  of  the  ganglionic  portion  of  the 
fifth  nerve  distributed  to  them  with  their  proper  motor  nerves. 

Through  branches  of  the  lesser  or  non-ganglionic  portion  of 
the  fifth,  the  muscles  of  mastication,  namely,  the  temporal, 
masseter,  two  pterygoid,  anterior  part  of  the  digastric,  and 
mylo-hyoid,  derive  their  motor  nerves.  The  motor  function 
of  these  branches  is  proved  by  the  violent  contraction  of  all 
the  muscles  of  mastication  in  experimental  irritation  of  the 
third,  or  inferior  maxillary,  division  of  the  nerve;  by  paralysis 
of  the  same  muscles,  when  it  is  divided  or  disorganized,  or 
from  any  reason  deprived  of  power ;  and  by  the  retention  of 
the  power  of  these  muscles,  when  all  those  supplied  by  the 
facial  nerve  lose  their  power  through  paralysis  of  that  nerve. 
The  last  instance  proves  best,  that  though  the  buccinator  mus- 
cle gives  passage  to,  and  receives  some  filaments  from,  a  buccal 
branch  of  the  inferior  division  of  the  fifth  nerve,  yet  it  derives 


THE     FIFTH     NERVE.  429 

its  motor  power  from  the  facial,  for  it  is  paralyzed  together 
with  the  other  muscles  that  are  supplied  by  the  facial,  but 
retaius  its  power  when  the  other  muscles  of  mastication  are 
paralyzed.  Whether,  however,  the  branch  of  the  fifth  nerve 
which  is  supplied  to  the  buccinator  muscle  is  entirely  sensi- 
tive, or  in  part  motor  also,  must  remain  for  the  present  doubt- 
ful. From  the  fact  that  this  muscle,  besides  its  other  func- 
tions, acts  in  concert  or  harmony  with  the  muscles  of  mastica- 
tion, in  keeping  the  food  between  the  teeth,  it  might  be  sup- 
posed from  analogy,  that  it  would  have  a  motor  branch  from 
the  same  nerve  that  supplies  them.  There  can  be  no  doubt, 
however,  that  the  so-called  buccal  branch  of  the  fifth,  is,  in 
the  main,  sensitive ;  although  it  is  not  quite  certain  that  it 
may  not  give  a  few  motor  filaments  to  the  buccinator  muscle. 

The  sensitive  function  of  the  branches  of  the  greater  divi- 
sion of  the  fifth  nerve  is  proved  by  all  the  usual  evidences, 
such  as  their  distribution  in  parts  that  are  sensitive  and  not 
capable  of  muscular  contraction,  the  exceeding  sensibility  of 
some  of  these  parts,  their  loss  of  sensation  when  the  nerve  is 
paralyzed  or  divided,  the  pain  without  convulsions  produced 
by  morbid  or  experimental  irritation  of  the  trunk  or  branches 
of  the  nerve,  and  the  analogy  of  this  portion  of  the  fifth  to  the 
posterior  root  of  the  spinal  nerve. 

But  although  formed  of  sensitive  filaments  exclusively,  the 
branches  of  the  greater  or  ganglionic  portion  of  the  fifth  nerve 
exercise  a  manifold  influence  on  the  movements  of  the  mus- 
cles of  the  head  and  face,  and  other  parts  in  which  they  are 
distributed.  They  do  so,  in  the  first  place,  by  providing  the 
muscles  themselves  with  that  sensibility  without  which  the 
mind,  being  unconscious  of  their  position  and  state,  cannot 
voluntarily  exercise  them.  It  is,  probably,  for  conferring 
this  sensibility  on  the  muscles,  that  the  branches  of  the  fifth 
nerve  communicate  so  frequently  with  those  of  the  facial  and 
hypoglossal,  and  the  nerves  of  the  muscles  of  the  eye ;  and  it 
is  because  of  the  loss  of  this  sensibility  that  when  the  fifth 
nerve  is  divided,  animals  are  always  slow  and  awkward  in  the 
movement  of  the  muscles  of  the  face  and  head,  or  hold  them 
still,  or  guide  their  movements  by  the  sight  of  the  objects 
towards  which  they  wish  to  move. 

Again,  the  fifth  nerve  has  an  indirect  influence  on  the  mus- 
cular movements,  by  conveying  sensations  of  the  state  and 
position  of  the  skin  and  other  parts :  which  the  mind  perceiv- 
ing, is  enabled  to  determine  appropriate  acts.  Thus,  when 
the  fifth  nerve  or  its  infra-orbital  branch  is  divided,  the  move- 
ments of  the  lips  in  feeding  may  cease,  or  be  imperfect ;  a  fact 
which  led  Sir  Charles  Bell  into  one  of  the  verv  few  errors  of  his 


430  THE    NERVOUS    SYSTEM. 

physiology  of  the  nerves.  He  supposed  that  the  motion  of 
the  upper  lip,  in  grasping  food,  depended  directly  on  the 
infra-orbital  nerve ;  for  he  found  that,  after  he  had  divided 
that  nerve  on  both  sides  in  an  ass,  it  no  longer  seized  the  food 
with  its  lips,  but  merely  pressed  them  against  the  ground,  and 
used  the  tongue  for  the  prehension  of  the  food.  Mr.  Mayo  cor- 
rected this  error.  He  found,  indeed,  that  after  the  infra-or- 
bital nerve  had  been  divided,  the  animal  did  not  seize  its  food 
with  the  lip,  and  could  not  use  it  well  during  mastication,  but 
that  it  could  open  the  lips.  He,  therefore,  justly  attributed 
the  phenomena  in  Sir  C.  Bell's  experiments  to  the  loss  of  sen- 
sation in  the  lips  ;  the  animal  not  being  able  to  feel  the  food, 
and,  therefore,  although  it  had  the  power  to  seize  it,  not  know- 
ing how  or  where  to  use  that  power. 

Lastly,  the  fifth  nerve  has  an  intimate  connection  with 
muscular  movements  through  the  many  reflex  acts  of  muscles 
of  which  it  is  the  necessary  excitant.  Hence,  when  it  is 
divided,  and  can  no  longer  convey  impressions  to  the  nervous 
centres  to  be  thence  reflected,  the  irritation  of  the  conjunctiva 
produces  no  closure  of  the  eye,  the  mechanical  irritation  of 
the  nose  excites  no  sneezing,  that  of  the  tongue  no  flowing  of 
saliva  ;  and  although  tears  and  saliva  may  flow  naturally, 
their  afflux  is  not  increased  by  the  mechanical  or  chemical  or 
other  stimuli,  to  the  indirect  or  reflected  influence  of  which  it 
is  liable  in  the  perfect  state  of  this  nerve. 

The  fifth  nerve,  through  its  ciliary  branches  and  the  branch 
which  forms  the  long  root  of  the  ciliary  or  ophthalmic  gan- 
glion, exercises  also  some  influence  on  the  movement  of  the 
iris.  When  the  trunk  of  the  ophthalmic  portion  is  divided, 
the  pupil  becomes,  according  to  Valentin,  contracted  in  men 
and  rabbits,  and  dilated  in  cats  and  dogs ;  but  in  all  cases, 
becomes  immovable,  even  under  all  the  varieties  of  the  stimu- 
lus of  light.  How  the  fifth  nerve  thus  affects  the  iris  is  unex- 
plained ;  the  same  effects  are  produced  by  destruction  of  the 
superior  cervical  ganglion  of  the  sympathetic,  so  that,  possibly, 
they  are  due  to  the  injury  of  those  filaments  of  the  sympathetic 
which,  after  joining  the  trunk  of  the  fifth,  at  and  beyond  the 
Gasserian  ganglion,  proceed  with  the  branches  of  its  oph- 
thalmic division  to  the  iris ;  or,  as  Dr.  R.  Hall  ingeniously 
suggests,  the  influence  of  the  fifth  nerve  on  the  movements  of 
the  iris  may  be  ascribed  to  the  affection  of  vision  in  conse- 
quence of  the  disturbed  circulation  or  nutrition  in  the  retina, 
when  the  normal  influence  of  the  fifth  nerve  and  ciliary  gan- 
glion is  disturbed.  In  such  disturbance,  increased  circulation 
making  the  retina  more  irritable  might  induce  extreme  con- 
traction of  the  iris  ;  or,  under  moderate  stimulus  of  light,  pro- 


THE     FIFTH     NERVE.  431 

ducing  partial  blindness,  might  induce  dilatation :  but  it  does 
not  appear  why,  if  this  be  the  true  explanation,  the  iris  should 
in  either  case  be  immovable  and  unaffected  by  the  various 
degrees  of  light. 

Furthermore,  the  morbid  effects  which  division  of  the  fifth 
nerve  produces  in  the  organs  of  special  sense,  make  it  prob- 
able that,  in  the  normal  state,  the  fifth  nerve  exercises  some 
indirect  influence  on  all  these  organs  or  their  functions.  Thus, 
after  such  division,  within  a  period  varying  from  twenty-four 
hours  to  a  week,  the  cornea  begins  to  be  opaque ;  then  it  grows 
completely  white;  a  low  destructive  inflammatory  process  en- 
sues in  the  conjunctiva,  sclerotica,  and  interior  parts  of  the 
eye ;  and  within  one  or  a  few  weeks,  the  whole  eye  may  be 
quite  disorganized,  and  the  cornea  may  slough  or  be  penetrated 
by  a  large  ulcer.  The  sense  of  smell  (and  not  merely  that  of 
mechanical  irritation  of  the  nose),  may  be  at  the  same  time 
lost,  or  gravely  impaired  ;  so  may  the  hearing,  and  commonly, 
whenever  the  fifth  nerve  is  paralyzed,  the  tongue  loses  the 
sense  of  taste  in  its  anterior  and  lateral  parts,  i.  e.,  in  the  por- 
tion in  which  the  lingual  or  gustatory  branch  of  the  inferior 
maxillary  division  of  the  fifth  is  distributed.1 

The  loss  of  the  sense  of  taste  is  no  doubt  chiefly  due  to  the 
lingual  branch  of  the  fifth  nerve  being  a  nerve  of  special 
sense ;  partly,  also,  perhaps,  it  is  due  to  the  fact  that  this  branch 
supplies,  in  the  anterior  and  lateral  parts  of  the  tongue,  a  nec- 
essary condition  for  the  proper  nutrition  of  that  part.  But, 
deferring  this  question  until  the  glosso-pharyngeal  nerve  is  to 
be  considered,  it  may  be  observed  that  in  some  brief  time  after 
complete  paralysis  or  division  of  the  fifth  nerve,  the  power  of 
all  the  organs  of  the  special  senses  may  be  lost ;  they  may  lose 
not  merely  their  sensibility  to  common  impressions,  for  which 
they  all  depend  directly  on  the  fifth  nerve,  but  also  their  sen- 
sibility to  the  several  peculiar  impressions  for  the  reception  and 
conduction  of  which  they  are  purposely  constructed  and  sup- 
plied with  special  nerves  besides  the  fifth.  The  facts  observed 
in  these  cases2  can,  perhaps,  be  only  explained  by  the  influence 
which  the  fifth  nerve  exercises  on  the  nutritive  processes  in  the 
organs  of  the  special  senses.  It  is  not  unreasonable  to  believe, 
that,  in  paralysis  of  the  fifth  nerve,  their  tissues  may  be  the 

1  That  complete  paralysis  of  the  fifth  nerve  may,  however,  be  un- 
accompanied, at  least,  for  a  considerable  period,  by  injury  to  the  or- 
gans of  special  sense,  with  the  exception  of  that  portion  of  the  tongue 
which  is  supplied  by  its  gustatory  branch,  is  well  illustrated  by  a  valu- 
able case  lately  recorded  by  Dr.  Althaus. 

2  Two  of  the  best  cases  are  published,  with  analyses  of  others,  by 
Mr.  Dixon,  in  the  Medico-Chirurgical  Transactions,  vol.  xxviii. 


432  THE    NERVOUS    SYSTEM. 

seats  of  such  changes  as  are  seen  in  the  laxity,  the  vascular 
congestion,  oedema,  and  other  affections  of  the  skin  of  the  face 
and  other  tegumentary  parts  which  also  accompany  the  pa- 
ralysis ;  and  that  these  changes,  which  may  appear  unimpor- 
tant when  they  affect  external  parts,  are  sufficient  to  destroy 
that  refinement  of  structure  by  which  the  organs  of  the  special 
senses  are  adapted  to  their  functions. 

According  to  Magendie  and  Longet,  destruction  of  the  eye 
ensues  more  quickly  after  division  of  the  trunk  of  the  fifth 
beyond  the  Gasserian  ganglion,  or  after  division  of  the  oph- 
thalmic branch,  than  after  division  of  the  roots  of  the  fifth 
between  the  brain  and  the  ganglion.  Hence  it  would  appear 
as  if  the  influence  on  nutrition  were  conveyed  through  the  fila- 
ments of  the  sympathetic,  which  join  the  branches  of  the  fifth 
nerve  at  and  beyond  the  Gasserian  ganglion,  rather  than 
through  the  filaments  of  the  fifth  itself;  and  this  is  confirmed 
by  experiments  in  which  extirpation  of  the  superior  cervical 
ganglion  of  the  sympathetic  produced  the  same  destructive 
disease  of  the  eye  that  commonly  follows  the  division  of  the 
fifth  nerve. 

And  yet,  that  the  filaments  of  the  fifth  nerve,  as  well  as 
those  of  the  sympathetic,  may  conduct  such  influence,  appears 
certain  from  the  cases,  including  that  by  Mr.  Stanley,  in 
which  the  source  of  the  paralysis  of  the  fifth  nerve  was  near 
the  brain,  or  at  its  very  origin,  before  it  receives  any  commu- 
nication from  the  sympathetic  nerve.  The  existence  of  gan- 
glia of  the  sympathetic  in  connection  with  all  the  principal 
divisions  of  the  fifth  nerve  where  it  gives  off  those  branches 
which  supply  the  organs  of  special  sense — for  example,  the 
connection  of  the  ophthalmic  ganglion  with  the  ophthalmic 
nerve  at  the  origin  of  the  ciliary  nerves ;  of  the  spheno-pala- 
tine  ganglion  with  the  superior  maxillary  division,  where  it 
gives  its  branches  to  the  nose  and  the  palate ;  of  the  otic  gan- 
glion with  the  inferior  maxillary  near  the  giving  off  of  fila- 
ments to  the  internal  ear;  and  of  the  submaxillary  ganglion 
with  the  lingual  branch  of  the  fifth — all  these  connections 
suggest  that  a  peculiar  and  probably  conjoint  influence  of  the 
sympathetic  and  fifth  nerves  is  exercised  in  the  nutrition  of 
the  organs  of  the  special  senses ;  and  the  results  of  experiment 
and  disease  confirm  this,  by  showing  that  the  nutrition  of  the 
organs  may  be  impaired  in  consequence  of  impairment  of  the 
power  of  either  of  the  nerves. 

A  possible  connection  between  the  fifth  nerve  and  the  sense 
of  sight,  is  shown  in  cases  of  no  unfrequent  occurrence,  in 
which  blows  or  other  injuries  implicating  the  frontal  nerve  as 
it  passes  over  the  brow,  are  followed  by  total  blindness  in  the 


THE    FACIAL    NERVE.  433 

corresponding  eye.  The  blindness  appears  to  be  the  conse- 
quence of  defective  nutrition  of  the  retina ;  for  although,  in 
some  cases,  it  has  ensued  immediately,  as  if  from  concussion 
of  the  retina,  yet  in  some  it  has  come  on  gradually  like  slowly 
progressive  amaurosis,  and  in  some  with  inflammatory  disor- 
ganization, followed  by  atrophy  of  the  whole  eye.1 

Physiology  of  the  Facial  Nerve. 

The  facial,  or  portio  dura  of  the  seventh  pair  of  nerves,  is 
the  motor  nerve  of  all  the  muscles  of  the  face,  including  the 
platysma,  but  not  including  any  of  the  muscles  of  mastication 
already  enumerated  (p.  428);  it  supplies,  also,  the  parotid 
gland,  and  through  the  connection  of  its  trunk  with  the 
Vidian  nerve,  by  the  petrosal  nerves,  some  of  the  muscles  of 
the  soft  palate,  most  probably  the  levator  palati  and  azygos 
uvulae  ;  by  its  tympanic  branches  it  supplies  the  stapedius 
and  laxator  tympani,  and,  through  the  otic  ganglion,  the  ten- 
sor tympani ;  through  the  chorda  tympani  it  sends  branches  to 
the  submaxillary  gland  and  to  the  lingualis  and  some  other 
muscular  fibres  of  the  tongue ;  and  by  branches  given  off  be- 
fore it  comes  upon  the  face,  it  supplies  the  muscles  of  the 
external  ear,  the  posterior  part  of  the  digastricus,  and  the 
stylo-hyoideus. 

To  the  greater  number  of  the  muscles  to  which  it  is  dis- 
tributed it  is  the  sole  motor  nerve.  No  pain  is  produced  by 
irritating  it  near  its  origin  (Valentin),  and  the  indications  of 
pain  which  are  elicited  when  any  of  its  branches  are  irritated 
may  be  explained  by  the  abundant  communications  which,  in 
all  parts  of  its  course,  it  forms  with  sensitive  nerves,  whose 
filaments  being  mingled  with  its  own  are  the  true  source  of  the 
pain. 

Besides  its  motor  influence,  the  facial  is  also,  by  means  of 
the  fibres  which  are  supplied  to  the  submaxillary  and  parotid 
glands,  a  so-called  secretory  nerve  (p.  377).  For  through  the 
last-named  branches  impressions  may  be  conveyed  which  excite 
increased  secretion  of  saliva.  For  example,  if,  in  a  dog,  the 
submaxillary  gland  be  exposed,  and  the  chorda  tympani  be 
divided,  it  will  be  seen  that  on  stimulating  the  distal  end  of 
the  nerve  by  a  weak  electric  current,  the  gland  becomes  ex- 
ceedingly vascular,  and  saliva  is  secreted  in  largely  increased 
amount.  Under  ordinary  circumstances  of  increased  secretion 
of  saliva  by  the  submaxillary  gland,  as  from  the  presence  of 

1  Such  H  case  is  recorded  by  Snabilie  in  the  Nederlandsch  Lancet, 
August,  1846. 


434  THE    NERVOUS    SYSTEM. 

food  in  the  mouth,  the  stimulus  is  conveyed  by  the  same 
channel,  the  chorda  tympani  being  the  efferent  nerve  in  a  reflex 
action,  in  which  the  afferent  fibres  are  branches  of  the  fifth 
and  glosso-pharyngeal  nerves. 

When  the  facial  nerve  is  divided,  or  in  any  other  way  par- 
alyzed, the  loss  of  power  in  the  muscles  which  it  supplies, 
while  proving  the  nature  and  extent  of  its  functions,  displays 
also  the  necessity  of  its  perfection  for  the  perfect  exercise  of 
all  the  organs  of  the  special  senses.  Thus,  in  paralysis  of  the 
facial  nerve,  the  orbicularis  palpebrarum  being  powerless,  the 
eye  remains  open  through  the  unbalanced  action  of  the  levator 
palpebrse;  and  the  conjunctiva,  thus  continually  exposed  to 
the  air  and  the  contact  of  dust,  is  liable  to  repeated  inflamma- 
tion, which  may  end  in  thickening  and  opacity  of  both  its  own 
tissue  and  that  of  the  cornea.  These  changes,  however,  ensue 
much  more  slowly  than  those  which  follow  paralysis  of  the 
fifth  nerve,  and  never  bear  the  same  destructive  character.  In 
paralysis  of  the  facial  nerve,  also,  tears  are  apt  to  flow  con- 
stantly over  the  face,  apparently  because  of  the  paralysis  of 
the  tensor  tarsi  muscle,  and  the  loss  of  the  proper  direction 
and  form  of  the  orifices  of  the  puncta  lachrymalia.  From 
these  circumstances,  the  sense  of  sight  is  impaired. 

The  sense  of  hearing,  also,  is  impaired  in  many  cases  of 
paralysis  of  the  facial  nerve;  not  only  in  such  as  are  instances 
of  simultaneous  disease  in  the  auditory  nerves,  but  in  such  as 
may  be  explained  by  the  loss  of  power  in  the  muscles  of  the 
internal  ear.  The  sense  of  smell  is  commonly  at  the  same 
time  impaired  through  the  inability  to  draw  air  briskly  to- 
wards the  upper  part  of  the  nasal  cavities,  in  which  part  alone 
the  olfactory  nerve  is  distributed ;  because,  to  draw  the  air  per- 
fectly in  this  direction,  the  action  of  the  dilators  and  com- 
pressors of  the  nostrils  should  be  perfect. 

Lastly,  the  sense  of  taste  is  impaired,  or  may  be  wholly  lost, 
in  paralysis  of  the  facial  nerve,  provided  the  source  of  the 
paralysis  be  in  some  part  of  the  nerve  between  its  origin  and 
the  giving  off  of  the  chorda  tympani.  This  result,  which  has 
been  observed  in  many  instances  of  disease  of  the  facial  nerve 
in  man,  appears  explicable  only  by  the  influence  which,  through 
the  chorda  tympani,  it  exercises  on  the  movements  of  the 
lingualis  and  the  adjacent  muscular  fibres  of  the  tongue ;  and, 
according  to  some,  or  probably  in  some  animals,  on  the  move- 
ments of  the  stylo-glossus.  We  may  therefore  suppose  that 
the  accurate  movement  of  these  muscles  in  the  tongue  is  in 
some  way  connected  with  the  proper  exercise  of  taste. 

Together  with  these  effects  of  paralysis  of  the  facial  nerve 
the  muscles  of  the  face  being  all  powerless,  the  countenance 


THE    GLOSSO-PHARYNGEAL     NERVE.          435 

acquires  on  the  paralyzed  side  a  characteristic,  vacant  look, 
from  the  absence  of  all  expression :  the  angle  of  the  mouth  ig 
lower,  and  the  paralyzed  half  of  the  mouth  looks  longer  than 
that  on  the  other  side :  the  eye  has  an  unmeaning  stare.  All 
these  peculiarities  increase,  the  longer  the  paralysis  lasts ;  and 
their  appearance  is  exaggerated  when  at  any  time  the  muscles 
of  the  opposite  side  of  the  face  are  made  active  in  any  expres- 
sion, or  in  any  of  their  ordinary  functions.  In  an  attempt  to 
blow  or  whistle,  one  side  of  the  mouth  and  cheek  acts  prop- 
erly, but  the  other  side  is  motionless,  or  flaps  loosely  at  the 
impulse  of  the  expired  air;  so  in  trying  to  suck,  one  side  only 
of  the  mouth  acts;  in  feeding,  the  lips  and  cheek  are  powerless, 
and  food  lodges  between  the  cheek  and  gum. 

As  a  nerve  of  expression,  the  seventh  nerve  must  not  be 
considered  independent  of  the  fifth  nerve,  with  which  it  forms 
so  many  communications ;  for,  although  it  is  through  the  facial 
nerve  alone  that  all  the  muscles  of  the  face  are  put  into  their 
naturally  expressive  actions,  yet  the  power  which  the  mind 
has  of  suppressing  or  controlling  all  these  expressions  can  only 
be  exercised  by  voluntary  and  well-educated  actions  directed 
through  the  facial  nerve  with  the  guidance  of  the  knowledge 
of  the  state  and  position  of  every  muscle,  and  this  knowledge 
is  acquired  only  through  the  fifth  nerve,  which  confers  sensi- 
bility on  the  muscles,  and  appears,  for  this  purpose,  to  be  more 
abundantly  supplied  to  the  muscles  of  the  face  than  any  other 
sensitive  nerve  is  to  those  of  other  parts. 

Physiology  of  the  Olosso-Pharyngeal  Nerve. 

The  glosso-pharyngeal  nerves  (4,  Fig.  151),  in  the  enume- 
ration of  the  cerebral  nerves  by  numbers  according  to  the  po- 
sition in  which  they  leave  the  cranium,  are  considered  as  di- 
visions of  the  eighth  pair  of  nerves,  in  which  term  are  included 
with  them  the  pneumogastric  and  accessory  nerves.  But  the 
union  of  the  nerves  under  one  term  is  inconvenient,  although 
in  some  parts  the  glosso-pharyngeal  and  pneumogastric  are  so 
combined  in  their  distribution  that  it  is  impossible  to  separate 
them  in  either  anatomy  or  physiology. 

The  glosso-pharyngeal  nerve  appears  to  give  filaments 
through  its  tympanic  branch  (Jacobson's  nerve),  to  the  fenestra 
ovalis,  and  feuestra  rotunda,  and  the  Eustachian  tube ;  also, 
to  the  carotid  plexus,  and,  through  the  petrosal  nerve,  to  the 
spheno-palatine  ganglion.  After  communicating,  either  within 
or  without  the  cranium,  with  the  pneumogastric,  and  soon  after 
it  leaves  the  cranium,  with  the  sympathetic,  digastric  branch 
of  the  facial,  and  the  accessory  nerve,  the  glosso-pharyngeal 


436  THE    NERVOUS    SYSTEM. 

nerve  parts  into  the  two  principal  divisions  indicated  by  its 
name,  and  supplies  the  mucous  membrane  of  the  posterior  and 
lateral  walls  of  the  upper  part  of  the  pharynx,  the  Eustachian 
tube,  the  arches  of  the  palate,  the  tonsils  and  their  mucous 
membrane,  and  the  tongue  as  far  forwards  as  the  foramen 
caecum  in  the  middle  line,  and  to  near  the  tip  at  the  sides  and 
inferior  part. 

Some  experiments  make  it  probable  that  the  glosso-pharyn- 
geal  nerve  contains,  even  at  its  origin,  some  motor  fibres,  to- 
gether with  those  of  common  sensation  and  the  sense  of  taste. 
Whatever  motor  influence,  however,  is  conveyed  directly 
through  the  branches  of  the  glosso-pharyngeal,  may  be  as- 
cribed to  the  filaments  of  the  pneumogastric  or  accessory  that 
are  mingled  with  it. 

The  experiments  of  Dr.  John  Reid,  confirming  those  of 
Panizza  and  Longet,  tend  to  the  same  conclusions ;  and  their 
results  probably  express  nearly  all  the  truth  regarding  the 
part  of  the  glosso-pharyngeal  nerve  which  is  distributed  to  the 
pharynx.  These  results  were  that, — 1.  Pain  was  produced 
when  the  nerve,  particularly  its  pharyngeal  branch,  was  irri- 
tated. 2.  Irritation  of  the  nerve  before  the  origin  of  its 
pharyngeal,  or  of  any  of  these  branches,  gave  rise  to  extensive 
muscular  motions  of  the  throat  and  lower  part  of  the  face:  but 
when  the  nerve  was  divided,  these  motions  were  excited  by 
irritating  the  upper  or  cranial  portion,  while  irritation  of  the 
lower  end,  or  that  in  connection  with  the  muscles,  was  followed 
by  no  movement ;  so  that  these  motions  must  have  depended 
on  a  reflex  influence  transmitted  to  the  muscles  through  other 
nerves  by  the  intervention  of  the  nervous  centres.  3.  When 
the  functions  of  the  brain  and  medulla  oblongata  were  arrested 
by  poisoning  the  animal  with  prussic  acid,  irritation  of  the 
glosso-pharyngeal  nerve,  before  it  was  joined  by  any  branches 
of  the  poeumogastric,  gave  rise  to  no  movements  of  the  muscles 
of  the  pharynx  or  other  parts  to  which  it  was  distributed ;  while, 
on  irritating  the  pharyngeal  branch  of  the  pneumogastric,  or 
the  glosso-pharyngeal  nerve,  after  it  had  received  the  com- 
municating branches  just  alluded  to,  vigorous  movements  of 
all  the  pharyngeal  muscles  and  of  the  upper  part  of  the  oesoph- 
agus followed. 

The  most  probable  conclusion,  therefore,  may  be  that  what 
motor  influence  the  glosso-pharyngeal  nerve  may  seem  to  exer- 
cise, is  due  either  to  the  filaments  of  the  pneumogastric  or  ac- 
cessory that  are  mingled  with  it,  or  to  impressions  conveyed 
through  it  to  the  medulla  oblongata,  and  thence  reflected  to 
muscles  through  motor  nerves,  especially  the  pneumogastric, 
accessory,  and  facial.  Thus,  the  glosso-pharyngeal  nerve  ex- 


THE    GLOSSO-PHARYNGEAL    NERVE.        437 

cites,  through  the  medium  of  the  medulla  obloDgata,  -the  ac- 
tions of  the  muscles  of  deglutition.  It  is  the  chief  centripetal 
nerve  engaged  in  these  actions ;  yet  not  the  only  one,  for,  as 
Dr.  John  Reid  has  shown,  the  acts  are  scarcely  disturbed  or 
retarded  when  both  the  glosso-pharyngeal  nerves  are  divided. 

But  besides  being  thus  a  nerve  of  common  sensation  in  the 
parts  which  it  supplies,  and  a  centripetal  nerve  through  which 
impressions  are  conveyed  to  be  reflected  to  the  adjacent  muscles, 
the  glosso-pharyngeal  is  also  a  nerve  of  special  sensation  ;  being 
the  gustatory  nerve,  or  nerve  of  taste,  in  all  the  parts  of  the 
tongue  to  which  it  is  distributed.  After  many  discussions,  the 
question,  which  is  the  nerve  of  taste  ? — the  lingual  branch  of 
the  fifth,  or  the  glosso-pharyngeal  ? — may  be  most  probably 
answered  by  stating  that  they  are  both  nerves  of  this  special 
function.  For  very  numerous  experiments  and  cases  have 
shown  that  when  the  trunk  of  the  fifth  nerve  or  its  lingual 
branch  is  paralyzed  or  divided,  the  sense  of  taste  is  completely 
lost  in  the  superior  surface  of  the  anterior  and  lateral  parts  of 
the  tongue.  The  loss  is  instantaneous  after  division  of  the 
nerve ;  and,  therefore,  cannot  be  ascribed  to  the  defective  nu- 
trition of  the  part,  though  to  this,  perhaps,  may  be  ascribed 
the  more  complete  and  general  loss  of  the  sense  of  taste  when 
the  whole  of  the  fifth  nerve  has  been  paralyzed. 

But,  on  the  other  hand,  while  the  loss  of  taste  in  the  part  of 
the  tongue  to  which  the  lingual  branch  of  the  fifth  nerve  is 
distributed  proves  that  to  be  a  gustatory  nerve,  the  fact  that 
the  sense  of  taste  is  at  the  same  time  retained  in  the  posterior 
and  postero-lateral  parts  of  the  tongue,  and  in  the  soft  palate 
and  its  anterior  arch,  to  which  (and  to  some  parts  of  which 
exclusively)  the  glosso-pharyngeal  is  distributed,  proves  that 
this  also  must  be  a  gustatory  nerve.  In  a  female  patient  at 
St.  Bartholomew's  Hospital,  the  left  lingual  branch  of  the  fifth 
nerve  was  divided  in  removing  a  portion  of  the  lower  jaw  :  she 
lost  both  common  sensation  and  the  sensation  of  taste  in  the 
tip  and  the  anterior  parts  of  the  left  half  of  the  tongue,  but 
retained  both  in  all  the  rest  of  the  tongue.  M.  Lisfranc  and 
others  have  noted  similar  cases ;  and  the  phenomena  in  them 
are  so  simple  and  clear,  that  there  can  scarcely  be  any  fallacy 
in  the  conclusion  that  the  lingual  branches  of  both  the  fifth 
and  the  glosso-pharyngeal  nerves  are  gustatory  nerves  in  the 
parts  of  the  tongue  which  they  severally  supply. 

This  conclusion  is  confirmed  by  some  experiments  on  ani- 
mals, and,  perhaps,  more  satisfactorily  as  concerns  the  sense  of 
taste  in  man,  by  observation  of  the  parts  of  the  tongue  and 
fauces,  in  which  the  sense  is  most  acute.  According  to  Valen- 
tin's experiments  made  on  thirty  students,  the  parts  of  the 

37 


438  THE     NERVOUS    SYSTEM. 

tongue  from  which  the  clearest  sensations  of  taste  are  derived, 
are  the  base,  as  far  as  the  foramen  caecum  and  lines  diverging 
forwards  on  each  side  from  it ;  the  posterior  palatine  arches 
down  to  the  epiglottis;  the  tonsils  and  upper  part  of  the 
pharynx  over  the  root  of  the  tongue.  These  are  the  seats  of 
the  distribution  of  the  glosso-pharyngeal  nerve.  The  anterior 
dorsal  surface,  and  a  portion  of  the  anterior  and  inferior  sur- 
face of  the  tongue,  in  which  the  lingual  branch  of  the  fifth  is 
alone  distributed,  conveyed  no  sense  of  taste  in  the  majority 
of  the  subjects  of  Valentin's  experiments ;  but  even  if  this  were 
generally  the  case,  it  would  not  invalidate  the  conclusion  that, 
in  those  who  have  the  sense  of  taste  in  the  anterior  and  upper 
part  of  the  tongue,  the  lingual  branch  of  the  fifth  is  the  nerve 
by  which  it  is  exercised. 

Physiology  of  the  Pneumogastric  Nerve. 

The  pneumogastrie  nerve,  nervus  vagus,  or  par  vagwn  (Fig. 
151),  has,  of  all  the  cranial  and  spinal  nerves,  the  most  various 
distribution,  and  influences  the  most  various  functions,  either 
through  its  own  filaments,  or  those  which,  derived  from  other 
nerves,  are  mingled  in  its  branches. 

The  parts  supplied  by  the  branches  of  the  pneumogastrie 
nerve  are  as  follows :  By  its  pharyngeal  branches,  which  enter 
the  pharyngeal  plexus,  a  large  portion  of  the  mucous  mem- 
brane, and,  probably,  all  the  muscles  of  the  pharynx ;  by  the 
superior  laryugeal  nerve,  the  mucous  membrane  of  the  under 
surface  of  the  epiglottis,  the  glottis,  and  the  greater  part  of 
the  larynx,  and  the  crico-thyroid  muscle ;  by  the  inferior 
laryngeal  nerve,  the  mucous  membrane  and  muscular  fibres 
of  the  trachea,  the  lower  part  of  the  pharynx  and  larynx,  and 
all  the  muscles  of  the  larynx,  except  the  crico-thyroid ;  by 
cesophageal  branches,  the  mucous  membrane  and  muscular 
coats  of  the  oesophagus.  Moreover,  the  branches  of  the  pneu- 
mogastrie nerve  form  a  large  portion  of  the  supply  of  nerves 
to  the  heart  and  the  great  arteries  through  the  cardiac  nerves, 
derived  from  both  the  trunk  and  the  recurrent  nerve  ;  to  the 
lungs,  through  both  the  anterior  and  the  posterior  pulmonary 
plexuses  ;  and  to  the  stomach,  by  its  terminal  branches  pass- 
ing over  the  walls  of  that  organ ;  while  branches  are  also  dis- 
tributed to  the  liver  and  to  the  spleen. 

From  the  parts  thus  enumerated  as  receiving  nerves  from 
the  pneumogastrie,  it  might  be  assumed  that  this  latter  is  a 
nerve  of  mixed  function,  both  sensitive  and  motor.  Experi- 
ments prove  that  it  is  so  from  its  origin,  for  the  irritation  of 
its  roots,  even  within  the  cranial  cavity,  produces  both  pain 


THE    PNEUMOGASTRIC     NERVE.  439 

and  convulsive  movements  of  the  larynx  and  pharynx  ;  and 
when  it  is  divided  within  the  skull,  the  same  movements  follow 
the  irritation  of  the  distal  portion,  showing  that  they  are  not 
due  to  reflex  action.  Similar  experiments  prove  that,  through 
its  whole  course,  it  contains  both  sensitive  and  motor  fibres, 
but  after  it  has  emerged  from  the  skull,  and,  in  some  instances 
even  sooner,  it  enters  into  so  many  anastomoses  that  it  is  hard 
to  say  whether  the  filaments  it  contains  are,  from  their  origin, 
its  own,  or  whether  they  are  derived  from  other  nerves  com- 
bining with  it.  This  is  particularly  the  case  with  the  filaments 
of  the  sympathetic  nerve,  which  are  abundantly  added  to 
nearly  all  the  branches  of  the  pneumogastric.  The  likeness 
to  the  sympathetic  which  it  thus  acquires  is  further  increased 
by  its  containing  many  filaments  derived,  not  from  the  brain, 
but  from  its  own  petrosal  ganglia,  in  which  filaments  originate, 
in  the  same  manner  as  in  the  ganglia  of  the  sympathetic,  so 
abundantly  that  the  trunk  of  the  nerve  is  visibly  larger  below 
the  ganglia  than  above  them  (Bidder  and  Volkmann).  Next  to 
the  sympathetic  nerve,  that  which  most  importantly  commu- 
nicates with  the  pneumogastric  is  the  accessory  nerve,  whose 
internal  branch  joins  its  trunk,  and  is  lost  in  it. 

Properly,  therefore,  the  pneumogastric  might  be  regarded 
as  a  triple-mixed  nerve,  having  out  of  its  own  sources,  motor, 
sensitive,  and  sympathetic  or  ganglionic  nerve-fibres ;  and  to 
this  natural  complexity  it  adds  that  which  it  derives  from  the 
reception  of  filaments  from  the  sympathetic,  accessory,  and 
cervical  nerves,  and,  probably,  the  glosso-pharyngeal  and 
facial. 

The  most  probable  account  of  the  particular  functions  which 
the  branches  of  the  pneumogastric  nerve  discharge  in  the  sev- 
eral parts  to  which  they  are  distributed,  may  be  drawn  from 
Dr.  John  Reid's  experiments  on  dogs.  They  show  that:  1. 
The  pharyngeal  branch  is  the  principal,  if  not  the  sole  motor 
nerve  of  the  pharynx  and  soft  palate,  and  is  most  probably 
wholly  motor ;  a  part  of  its  motor  fibres  being  derived  from 
the  internal  branch  of  the  accessory  nerve.  2.  The  inferior 
laryngeal  nerve  is  the  motor  nerve  of  the  larynx,  irritation  of 
it  producing  vigorous  movements  of  the  arytenoid  cartilages  ; 
while  irritation  of  the  superior  laryngeal  nerve  gives  rise  to  no 
action  in  any  of  the  muscles  attached  to  the  arytenoid  carti- 
lages, but  merely  to  contractions  of  the  crico-thyroid  muscle. 
3.  The  superior  laryngeal  nerve  is  chiefly  sensitive;  the  in- 
ferior, for  the  most  part,  motor ;  for  division  of  the  recurrent 
nerves  puts  an  end  to  the  motions  of  the  glottis,  but  without 
lessening  the  sensibility  of  the  mucous  membrane  ;  and  division 
of  the  superior  laryngeal  nerves  leaves  the  movements  of  the 


440  THE    NERVOUS    SYSTEM. 

glottis  unaffected,  but  deprives  it  of  its  sensibility.  4.  The 
motions  of  the  oasophagus  are  dependent  on  motor  fibres  of 
the  pneumogastric,  and  are  probably  excited  by  impressions 
made  upon  sensitive  fibres  of  the  same ;  for  irritation  of  its 
trunk  excites  motions  of  the  oesophagus,  which  extend  over 
the  cardiac  portions  of  the  stomach  ;  and  division  of  the  trunk 
paralyzes  the  ossophagus,  which  then  becomes  distended  with 
the  food.  5.  The  cardiac  branches  of  the  pneumogastric 
nerve  are  one,  but  not  the  sole  channel  through  which  the  in- 
fluence of  the  central  organs  and  of  mental  emotions  is  trans- 
mitted to  the  heart.  6.  The  pulmonary  branches  form  the 
principal,  but  not  the  sole  channel  by  which  the  impressions 
on  the  mucous  surface  of  the  lungs  that  excite  respiration,  are 
transmitted  to  the  medulla  oblongata.  Dr.  Keid  was  unable 
to  determine  whether  they  contain  motor  fibres. 

From  these  results,  and  by  referring  to  what  has  been  said 
in  former  chapters,  the  share  which  the  pneumogastric  nerve 
takes  in  the  functions  of  the  several  parts  to  which  it  sends 
branches  may  be  understood  : 

1.  In  deglutition,  the  motions  of  the  pharynx  are  of  the 
reflex  kind.     The  stimulus  of  the  food  or  other  substance  to 
be  swallowed,  acting  on  the  filaments  of  the  glosso-pharyngeal 
nerve  as  well  as  the  filaments  of  the  superior  laryngeal  given 
to  the  pharynx,  and  of  some  other  nerves,  perhaps,  with  which 
these  communicate,  is  conducted  to  the  medulla  oblongata, 
whence  it  is  reflected,  chiefly  through  the  pneumogastric,  to 
the  muscles  of  the  pharynx. 

2.  In  the  functions  of  the  larynx,  the  sensitive  filaments  of 
the  pneumogastric  supply  that  acute  sensibility  by  which  the 
glottis  is  guarded  against  the  ingress  of  foreign  bodies,  or  of 
irrespirable  gases.     The  contact  of  these  stimulates  the  fila- 
ments of  the  superior  laryngeal  branch  of  the  pneumogastric ; 
and  the  impression  conveyed  to  the  medulla  oblongata,  whe- 
ther it  produce  sensation  or  not,  is  reflected  to  the  filaments  of 
the  recurrent  or  inferior  laryngeal  branch,  and  excites  con- 
traction of  the  muscles  that  close  the  glottis.      Both  these 
branches  of  the  pneumogastric  co-operate  also  in  the  produc- 
tion and  regulation  of  the  voice ;  the  inferior  laryngeal  deter- 
mining the  contraction  of  the  muscles  that  vary  the  tension  of 
the  vocal  cords,  and  the  superior  laryngeal  conveying  to  the 
mind  the  sensations  of  the  state  of  these  muscles  necessary  for 
their  continuous  guidance.     And  both  the  branches  co-operate 
in  the  actions  of  the  larynx  in  the  ordinary  slight  dilatation 
and  contraction  of  the  glottis  in  the  acts  of  expiration  and 
inspiration,  and  more  evidently  in  those  of  coughing  and  other 
forcible  respiratory  movements  (p.  182). 


THE    PNEUMOGASTRIC    NERVE.  441 

3.  It  is  partly  through  their  influence  on  the  sensibility  and 
muscular  movements  in  the  larynx,  that  the  pneumogastric 
nerves  exercise  so  great  an  influence  on  the  respiratory  pro- 
cess, and  that  the  division  of  both  the  nerves  is  commonly 
fatal.  To  determine  how  death  is  in  these  cases  produced,  has 
been  the  object  of  innumerable,  and  often  contradictory,  ex- 
periments. It  is  probably  produced  differently  in  different 
cases,  and  in  many  is  the  result  of  several  co-operating  causes. 
Thus,  after  division  of  both  the  nerves,  the  respiration  at  once 
becomes  slower,  the  number  of  respirations  in  a  given  time 
being  commonly  diminished  to  one-half,  probably  because  the 
pneumogastric  nerves  are  the  principal  conductors  of  the  im- 
pression of  the  necessity  of  breathing  to  the  medulla  oblon- 
gata.  Respiration  does  not  cease ;  for  it  is  probable  that  the 
impression  may  be  conveyed  to  the  medulla  oblongata  through 
the  sensitive  nerves  of  all  parts  in  which  the  imperfectly 
aerated  blood  flows  (see  p.  407):  yet  the  respiration  being  re- 
tarded, adds  to  the  other  injurious  effects  of  division  of  the 
nerves. 

Again,  division  of  both  pneumogastric  trunks,  or  of  both 
their  recurrent  branches,  is  often  very  quickly  fatal  in  young 
animals ;  but  in  old  animals  the  division  of  the  recurrent  nerve 
is  not  generally  fatal,  and  that  of  both  the  pneumogastric 
trunks  is  not  always  fatal  (J.  Reid),  and,  when  it  is  so,  the 
death  ensues  slowly.  This  difference  is,  probably,  because  the 
yielding  of  the  cartilages  of  the  larynx  in  young  animals  per- 
mits the  glottis  to  be  closed  by  the  atmospheric  pressure  in  in- 
spiration, and  they  are  thus  quickly  suffocated  unless  trache- 
otomy be  performed  (Legallois).  In  old  animals,  the  rigidity 
and  prominence  of  the  arytenoid  cartilages  prevent  the  glottis 
from  being  completely  closed  by  the  atmospheric  pressure ;  even 
when  all  the  muscles  are  paralyzed,  a  portion  at  its  posterior 
part  remains  open,  and  through  this  the  animal  continues  to 
breathe.  Yet  the  diminution  of  the  orifice  for  respiration  may 
add  to  the  difficulty  of  maintaining  life. 

In  the  case  of  slower  death,  after  division  of  both  the  pneu- 
mogastric nerves,  the  lungs  are  commonly  found  gorged  with 
blood,  oadematous,  or  nearly  solid,  or  with  a  kind  of  low  pneu^ 
monia,  and  with  their  bronchial  tubes  full  of  frothy  bloody 
fluid  and  mucus,  changes  to  which,  in  general,  the  death  may  be 
proximately  ascribed.  These  changes  are  due,  perhaps  in  part, 
to  the  influence  which  the  pneumogastric  nerves  exercise  on  the 
movements  of  the  air-cells  and  bronchi ;  yet,  since  they  are  not 
always  produced  in  one  lung  when  its  pneumogastric  nerve  is 
divided,  they  cannot  be  ascribed  wholly  to  the  suspension  of 
organic  nervous  influence  (J.  Reid).  Rather,  they  may  be 


442  THE    NERVOUS    SYSTEM. 

ascribed  to  the  hindrance  to  the  passage  of  blood  through  the 
lungs,  in  consequence  of  the  diminished  supply  of  air  and  the 
excess  of  carbonic  acid  in  the  air-cells  and  in  the  pulmonary 
capillaries  (see  p.  187) ;  in  part,  perhaps,  to  paralysis  of  the 
bloodvessels,  leading  to  congestion ;  and  in  part,  also,  as  the 
experiments  of  Traube  especially  show,  they  appear  due  to  the 
passage  of  food  and  of  the  various  secretions  of  the  mouth  and 
fauces  through  the  glottis,  which,  being  deprived  of  its  sensi- 
bility, is  no  longer  stimulated  or  closed  in  consequence  of  their 
contact.  He  says,  that  if  the  trachea  be  divided  and  separated 
from  the  oesophagus,  or  if  only  the  oesophagus  be  tied,  so  that 
no  food  or  secretion  from  above  can  pass  down  the  trachea,  no 
degeneration  of  the  tissue  of  the  lungs  will  follow  the  division 
of  the  pneumogastric  nerves.  So  that,  on  the  whole,  death 
after  division  of  the  pneumogastric  nerves  may  be  ascribed, 
when  it  occurs  quickly  in  young  animals,  to  suffocation  through 
mechanical  closure  of  the  paralyzed  glottis :  and,  when  it  occurs 
more  slowly,  to  the  congestion  and  pneumonia  produced  by 
the  diminished  supply  of  air,  by  paralysis  of  the  bloodvessels, 
and  by  the  passage  of  foreign  fluids  into  the  bronchi ;  and  ag- 
gravated by  the  diminished  frequency  of  respiration,  the  in- 
sensibility to  the  diseased  state  of  the  lungs,  the  diminished 
aperture  of  the  glottis,  and  the  loss  of  the  due  nervous  influ- 
ence upon  the  process  of  respiration. 

4.  Respecting  the  influence  of  the  pueumogastric  nerves  on 
the  movements  of  the  oesophagus  and  stomach,  the  secretion 
of  gastric  fluid,  the  sensation  of  hunger,  absorption  by  the 
stomach,  and  the  action  of  the  heart,1  former  pages  may  be 
referred  to. 

Cyon  and  Ludwig  have  discovered  that  a  remarkable  power 
appears  to  be  exercised  on  the  dilatation  of  the  bloodvessels 
by  a  small  nerve,  which  arises,  in  the  rabbit,  from  the  superior 
laryngeal  branch,  or  from  this  and  the  trunk  of  the  pneumo- 
gastric nerve,  and  after  communicating  with  filaments  of  the 
inferior  cervical  ganglion  proceeds  to  the  heart.  If  this  nerve 
be  divided,  and  its  upper  extremity  be  stimulated  by  a  weak 
interrupted  current,  an  inhibitory  influence  is  conveyed  to  the 
vaso-motor  centre  in  the  medulla  oblongata  (p.  452),  so  as  to 
cause,  by  reflex  action,  dilatation  of  the  principal  bloodvessels, 
with  diminution  of  the  force  and  frequency  of  the  heart's 
action.  From  the  remarkable  lowering  of  the  blood-pressure 
in  the  vessels,  thus  produced,  this  branch  of  the  vagus  is  called 
the  depressor  nerve ;  and  it  is  presumed,  as  an  afferent  nerve 
of  the  heart,  to  be  the  means  of  conveying  to  the  vaso-motor 

1  See  foot-note,  p.  453. 


THE    SPINAL    ACCESSORY    NERVE.  443 

centre  in  the  medulla  indications  of  such  conditions  of  the 
heart  as  require  a  lowering  of  the  blood  pressure  in  the  vessels; 
as,  for  example,  when  the  heart  cannot,  with  sufficient  ease, 
propel  blood  into  the  already  too  full  or  too  tense  arteries. 

Physiology  of  the  Spinal  Accessory  Nerve. 

In  the  preceding  pages  it  is  implied  that  all  the  motor  in- 
fluence which  the  pneumogastric  nerves  exercise,  is  conveyed 
through  filaments,  which,  from  their  origin,  belong  to  them; 
and  this  is,  perhaps,  true.  Yet  a  question,  which  has  been 
often  discussed,  may  still  be  entertained,  whether  a  part  of  the 
motor  filaments  that  appear  to  belong  to  the  pneumogastric 
nerves  are  not  given  to  them  from  the  accessory  nerves  ? 

The  principal  branch  of  the  accessory  nerve,  its  external 
branch,  supplies  the  sterno-mastoid  and  trapezius  muscles;  and 
though  pain  is  produced  by  irritating  it,  is  composed  almost 
exclusively  of  motor  fibres.  It  might  appear  very  probable, 
therefore,  that  the  internal  branch,  which  is  added  to  the 
trunk  of  the  pneumogastric  just  before  the  giving  off  of  the 
pharyngeal  branch,  is  also  motor;  and  that  through  it  the 
pneumogastric  nerve  derives  part  of  the  motor  fibres  which  it 
supplies  to  the  muscles  enumerated  above.  And  further,  since 
the  pneumogastric  nerve  has  a  ganglion  just  above  the  part  at 
which  the  internal  branch  of  the  accessory  nerve  joins  its 
trunk,  a  close  analogy  may  seem  to  exist  between  these  two 
nerves  and  the  spinal  nerves  with  their  anterior  and  posterior 
roots.  In  this  view,  Arnold  and  several  later  physiologists 
have  regarded  the  accessory  nerve  as  constituting  a  motor  root 
of  the  vagus  nerve ;  and  although  this  view  cannot  now  be 
maintained,  yet  it  is  very  probable  that  the  accessory  nerve 
gives  some  motor  filaments  to  the  pneumogastric.  For,  among 
the  experiments  made  on  this  point,  many  have  shown  that 
when  the  accessory  nerve  is  irritated  within  the  skull,  convul- 
sive movements  ensue  in  some  of  the  muscles  of  the  larynx ; 
all  of  which,  as  already  stated,  are  supplied,  apparently,  by 
branches  of  the  pneumogastric ;  and  (which  is  a  very  signifi- 
cant fact)  Vrolik  states  that  in  the  chimpanzee  the  internal 
branch  of  the  accessory  does  not  join  the  pneumogastric  at  all, 
but  goes  direct  to  the  larynx.  On  the  whole,  therefore,  al- 
though in  some  of  the  experiments  no  movements  in  the  larynx 
followed  irritation  of  the  accessory  nerve,  yet  it  may  be  con- 
cluded that  this  nerve  gives  to  the  pneumogastric  some  of  the 
motor  filaments  which  pass,  with  the  laryngeal  branches,  to 
the  muscles  of  the  larynx,  especially  to  the  crico-thyroid  (Ber- 
nard) ;  although  it  is  certain  that  the  accessory  nerve  does  not 


444  THE    NERVOUS    SYSTEM. 

supply  all  the  motor  filaments  which  the  branches  of  the  pneu- 
mogastric  contain. 

Among  the  roots  of  the  accessory  nerve,  the  lower,  arising 
from  the  spinal  cord,  appear  to  be  composed  exclusively  of 
motor  fibres,  and  to  be  destined  entirely  to  the  trapezius  and 
sterno-mastoid  muscles ;  the  upper  fibres,  arising  from  the 
medulla  oblongata,  contain  many  sensitive  as  well  as  motor 
fibres. 

Physiology  of  the  Hypoglossal  Nerve. 

The  hypoglossal  or  ninth  nerve,  or  motor  linguce,  has  a  pe- 
culiar relation  to  the  muscles  connected  with  the  hyoid  bone, 
including  those  of  the  tongue.  It  supplies  through  its  de- 
scending branch  (descendens  noni\  the  sterno-hyoid,  sterno- 
thyroid,  and  omo-hyoid ;  through  a  special  branch  the  thyro- 
hyoid,  and  through  its  lingual  branches  the  genio-hyoid, 
stylo-glossus,  hyo-glossus,  and  genio-hyoglossus  and  linguales. 
It  contributes,  also,  to  the  supply  of  the  submaxillary  gland. 

The  function  of  the  hypoglossal  is,  probably,  exclusively 
motor.  As  a  motor  nerve,  its  influence  on  all  the  muscles 
enumerated  above  is  shown  by  their  convulsions  when  it  is 
irritated,  and  by  their  loss  of  power  when  it  is  paralyzed. 
The  effects  of  the  paralysis  of  one  hypoglossal  nerve  are,  how- 
ever, not  very  striking  in  the  tongue.  Often,  in  cases  of  hemi- 
plegia  involving  the  functions  of  the  hypoglossal  nerve,  it  is 
not  possible  to  observe  any  deviation  in  the  direction  of  the 
protruded  tongue ;  probably  because  the  tongue  is  so  compact 
and  firm  that  the  muscles  on  either  side,  their  insertion  being 
nearly  parallel  to  the  median  line,  can  push  it  straight  for- 
wards or  turn  it  for  some  distance  towards  either  side. 


Physiology  of  the  Spinal  Nerves. 

Little  need  be  added  to  what  has  been  already  said  of  these 
nerves  (pp.  390  to  392).  The  anterior  roots  of  the  spinal 
nerves  are  formed  exclusively  of  motor  fibres ;  the  posterior 
roots  exclusively  of  sensitive  fibres. 

Beyond  the  ganglia  all  the  spinal  nerves  appear  to  be 
mixed  nerves,  and  to  contain  as  well  sympathetic  filaments. 

Of  the  functions  of  the  ganglia  of  the  spinal  nerves  nothing 
very  definite  is  known.  That  they  are  not  the  reflectors  of 
any  of  the  ascertained  reflex  actions  through  the  spinal 
nerves,  is  shown  by  the  reflex  movements  ceasing  when  the 
posterior  roots  are  divided  between  the  ganglia  and  the  spinal 
cord. 


THE    SYMPATHETIC    NERVE.  445 


PHYSIOLOGY   OF   THE   SYMPATHETIC    NERVE. 

The  sympathetic  nerve,  or  sympathetic  system  of  nerves, 
obtained  its  name  from  the  opinion  that  it  is  the  means 
through  which  are  effected  the  several  sympathies  in  morbid 
action  which  distant  organs  manifest.  It  has  also  been  called 
the  nervous  system  of  organic  life,  upon  the  supposition,  now 
proved  erroneous,  that  it  alone,  as  a  nervous  system,  influences 
the  organic  processes.  Both  terms  are  defective ;  but,  since 
the  title  sympathetic  nerve  has  the  advantage  of  long  and  most 
general  custom  in  its  favor,  and  is  not  more  inaccurate  than 
the  other,  it  will  be  here  employed. 

The  general  differences  between  the  fibres  of  the  cerebro- 
spinal  and  sympathetic  nerves  have  been  already  stated  (p. 
371) ;  and  it  has  been  said,  that  although  such  general  differ- 
ences exist,  and  are  sufficiently  discernible  in  selected  filaments 
of  each  system  of  nerves,  yet  they  are  neither  so  constant,  nor 
of  such  a  kind,  as  to  warrant  the  supposition,  that  the  different 
modes  of  action  of  the  two  systems  can  be  referred  to  the  dif- 
ferent structures  of  their  fibres.  Kather,  it  is  probable,  that 
the  laws  of  conduction  by  the  fibres  are  in  both  systems  the 
same,  and  that  the  differences  manifest  in  the  modes  of  action 
of  the  systems  are  due  to  the  multiplication  and  separation  of 
the  nervous  centres  of  the  sympathetic :  ganglia,  or  nerve- 
centres,  being  placed  in  connection  with  the  fibres  of  the  sym- 
pathetic in  nearly  all  parts  of  their  course. 

According  to  the  most  general  view,  the  sympathetic  system 
may  be  described  as  arranged  in  two  principal  divisions,  each 
of  which  consists  of  ganglia  and  connecting  fibres.  The  first 
division  may  include  those  ganglia  which  are  seated  on  and 
involve  the  main  trunks  or  branches  of  cerebral  and  spinal 
nerves.  This  division  will  include  the  large  Gasserian  gan- 
glion on  the  sensitive  trunk  of  the  fifth  cerebral  nerve  (Fig. 
152),  the  ganglia  on  the  glosso-pharyngeal  and  pneumogastric 
nerves,  and  the  ganglia  on  the  posterior  or  sensitive  branches 
of  the  spinal  nerves  (Fig.  141). 

To  the  second  division  belong  the  double  chain  of  praeverte- 
bral  ganglia  (24,  30,  Fig.  151)  and  their  branches,  extend- 
ing from  the  interior  and  base  of  the  skull  to  the  coccyx  ;  the 
various  sympathetic  visceral  plexuses  and  their  ganglia,  as  the 
cardiac,  the  solar,  the  renal  and  hypogastric  plexuses  ;  and  in 
the  same  division  may  be  included  the  ganglia  in  the  neigh- 
borhood of  the  head  and  neck,  namely,  the  ophthalmic  or  len- 
ticular, the  spheno-palatine,  the  otic,  and  the  submaxillary 
ganglia  (Fig.  152). 

38 


446  THE    NERVOUS    SYSTEM. 

FIG.  151. 


Distribution  of  the  eighth  pair  of  nerves  on  the  left  side  (from  Hirschfeld  and 

Leveill6). 

1,  Gasserian  ganglion  of  fifth  nerve;  2,  internal  carotid  artery;  3,  pharyngeal 
branch  of  pneumogastric ;  4,  glosso-pharyngeal  nerve ;  5,  lingual  nerve  (fifth) ;  6, 
spinal-accessory  nerve ;  7,  middle  constrictor  of  pharynx ;  8,  internal  jugular  vein 
(cut);  9,  superior  laryngeal  nerve;  10,  ganglion  of  trunk  of  pneumogastric  nerve; 
11,  hypoglossal  nerve  (cut)  on  hyoglossus ;  12,  ditto  (cut)  communicating  with  eighth 


THE    SYMPATHETIC    NERVE.  447 

The  structure  of  all  these  ganglia  appears  to  be  essentially 
similar,  all  containing — 1st,  nerve-fibres  traversing  them ; 
2dly,  nerve-fibres  originating  in  them  ;  3dly,  nerve-  or  ganglion- 
corpuscles,  giving  origin  to  these  fibres ;  and  4thly,  other  cor- 
puscles that  appear  free.  And  in  the  trunk,  and  thence  pro- 
ceeding branches  of  the  sympathetic,  there  appear  to  be  al- 
ways— 1st,  fibres  which  arise  in  its  own  ganglia ;  2dly,  fibres 
derived  from  the  ganglia  of  the  cerebral  and  spinal  nerves ; 
3dly,  fibres  derived  from  the  brain  and  spinal  cord  and  trans- 
mitted through  the  roots  of  their  nerves.  The  spinal  cord, 
indeed,  appears  to  furnish  a  large  source  of  the  fibres  of  the 
sympathetic  nerve. 

Respecting  the  course  of  the  filaments  belonging  to  the  sym- 
pathetic, the  following  appears  to  have  been  determined.  Of 
the  filaments  derived  from  the  ganglia  on  the  cerebral  nerves, 
some  may  pass  towards  the  brain ;  for,  in  the  trunks  of  the 
nerves,  between  the  ganglia  and  the  brain,  fine  filaments  like 
those  of  the  sympathetic  are  found.  But  these  may  be  pro- 
ceeding from  the  brain  to  the  ganglia ;  and,  on  the  whole,  it  is 
probable  that  nearly  all  the  filaments  originating  in  the 
ganglia  or  cerebral  nerves,  go  out  towards  the  tissues  and  or- 
gans to  be  supplied,  some  of  them  being  centrifugal,  some  cen- 
tripetal ;  so  that  each  ganglion  with  its  outgoing  filaments  may 
form  a  kind  of  special  nervous  system  appropriated  to  the 
part  in  which  its  filaments  are  placed.  Such,  for  example, 
may  be  the  ophthalmic  ganglion  with  the  ciliary  nerves,  con- 
nected with  the  brain  and  the  rest  of  the  sympathetic  system 
by  the  branches  of  the  third,  fifth,  and  sympathetic  nerves 
that  form  its  roots,  yet,  by  filaments  of  its  own,  controlling  in 
some  mode  and  degree,  the  processes  in  the  interior  of  the  eye. 

Of  the  fibres  that  arise  in  the  spinal  ganglia,  some  appear 
to  pass  into  the  posterior  branches  of  the  spinal  nerves,  and 
to  be  distributed  with  them ;  the  rest  pass  through  the  branches 
by  which  the  spinal  nerves  communicate  with  the  trunks  of 
the  sympathetic,  and  then  entering  the  sympathetic  are  disr 
tributed  with  its  branches  to  the  viscera.  With  these,  also  a 

and  first  cervical  nerve ;  13,  external  laryngeal  nerve ;  14,  Second  cervical  nerve  loop- 
ing with  first;  15,  pharyngeal  plexus  on  inferior  constrictor;  16,  superior  cervical 
ganglion  of  sympathetic ;  17,  superior  cardiac  nerve  of  pneumogastric ;  18,  third  cer- 
vical nerve  ;  19,  thyroid  body;  20,  fourth  cervical  nerve ;  21,  21,  left  recurrent  laryn- 
geal nerve;  22,  spinal-accessory,  communicating  with  cervical  nerves;  23,  trachea; 
24,  middle  cervical  ganglion  of  sympathetic ;  25,  middle  cardiac  nerve  of  pneumo- 
gastric ;  26,  phrenic  nerve  (cut) ;  27,  left  carotid  artery  (cut) ;  28,  brachial  plexus ;  29, 
phrenic  nerve  (cut);  30,  inferior  cervical  ganglion  of  sympathetic;  31,  pulmonary 
plexus  of  pneuraogastric ;  32,  arch  of  the  thoracic  aorta ;  33,  cesophageal  plexus ;  34, 
vena  azygos  superior;  35,  vena  azygos  minor;  36,  gangliated  cord  of  sympathetic. 


448 


THE    NERVOUS    SYSTEM. 


certain  number  of  the  large  ordinary  cerebro-spinal  nerve- 
fibres,  after  traversing  the  ganglia,  pass  into  the  sympathetic. 


FIG.  152. 


General  plan  of  the  branches  of  the  fifth  pair  (after  a  sketch  by  Charles  Bell).  yz. 
1,  lesser  root  of  the  fifth  pair ;  2,  greater  root  passing  forwards  into  the  Gasserian 
ganglion  ;  3,  placed  on  the  bone  above  the  ophthalmic  nerve,  which  is  seen  dividing 
into  the  supra-orbital,  lachrymal,  and  nasal  branches,  the  latter  connected  with  the 
ophthalmic  ganglion ;  4,  placed  on  the  bone  close  to  the  foramen  rotundum,  marks 
the  superior  maxillary  division,  which  is  connected  below  with  the  spheno-palatine 
ganglion,  and  passes  forwards  to  the  infra-orbital  foramen ;  5,  placed  on  the  bone 
over  the  foramen  ovale,  marks  the  submaxillary  nerve,  giving  off  the  anterior  au- 
ricular and  muscular  branches,  and  continued  by  the  inferior  dental  to  the  lower 
jaw,  and  by  the  gustatory  to  the  tongue  ;  a,  the  submaxillary  gland,  the  submaxillary 
ganglion  placed  above  it  in  connection  with  the  gustatory  nerve ;  6,  the  chorda 
tympani ;  7,  the  facial  nerve  issuing  from  the  stylo-mastoid  foramen. 

Of  the  fibres  derived  from  the  ganglia  of  the  sympathetic 
itself,  some  go  straightway  towards  the  viscera,  the  rest  pass 
through  the  branches  of  communication  between  the  sympa- 
thetic and  the  branches  of  the  spinal  nerves,  and  joining  these 
spinal  nerves,  proceed  with  them  to  their  respective  seats  of 
distribution,  especially  to  the  more  sensitive  parts. 


THE    SYMPATHETIC    NERVE.  449 

Thus,  through  these  communicating  branches,  which  have 
been  generally  called  roots  or  origins  of  the  'sympathetic  nerve, 
an  interchange  is  effected  between  all  the  spinal  nerves  and 
the  sympathetic  trunks ;  all  the  ganglia,  also,  which  are  seated 
on  the  cerebral  nerves,  have  roots  (as  they  are  called)  through 
which  filaments  of  the  cerebral  nerves  are  added  to  their  own. 
So  that,  probably,  all  sympathetic  nerves  contain  some  inter- 
mingled cerebral  or  spinal  nerve-fibres ;  and  all  cerebral  and 
spinal  nerves  some  filaments  derived  from  the  sympathetic 
system  or  from  ganglia.  But  the  proportions  in  which  these 
filaments  are  mingled  are  not  uniform.  The  nerves  which 
arise  from  the  brain  and  spinal  cord  retain  throughout  their 
course  and  distribution  a  preponderance  of  cerebro-spinal  fibres, 
while  the  nerves  immediately  arising  from  the  so-called  sym- 
pathetic ganglia  probably  contain  a  majority  of  sympathetic 
fibres.  But  inasmuch  as  there  is  no  certainty  that  in  struc- 
ture the  branches  of  cerebral  or  spinal  nerves  differ  always 
from  those  of  the  sympathetic  system,  it  is  impossible  in  the 
present  state  of  our  knowledge  to  be  sure  of  the  source  of 
fibres  which  from  their  structure  might  lead  the  observer  to 
believe  that  they  arose  from  the  brain  or  spinal  cord  on  the 
one  hand,  or  from  the  sympathetic  ganglia  on  the  other.  In 
other  words,  although  the  large  white  tubular  fibres  are  espe- 
cially characteristic  of  cerebro-spinal  nerves,  and  the  pale  or 
gelatinous  fibres  of  a  sympathetic  nerve,  in  which  they  largely 
preponderate,  there  is  no  certainty  to  be  obtained  in  a  doubt- 
ful case,  of  whether  the  nerve-fibre  is  derived  from  one  or  the 
other,  from  mere  examination  of  its  structure.  It  may  be  de- 
rived from  either  source. 

With  respect  to  the  functions  of  the  sympathetic  nervous 
system,  it  may  be  stated  generally  that  the  sympathetic  nerve- 
fibres  are  simple  conductors  of  impressions,  as  those  of  the 
cerebro-spinal  system  are,  and  that  the  ganglionic  centres  have 
(each  in  its  appropriate  sphere)  the  like  powers  both  of  con- 
ducting and  of  communicating  impressions.  Their  power  of 
conducting  impressions  is  sufficiently  proved  in  ordinary  dis- 
eases, as  when  any  of  the  viscera,  usually  unfelt,  give  rise  to 
sensations  of  pain,  or  when  a  part  not  commonly  subject  to 
mental  influence  is  excited  or  retarded  in  its  actions  by  the 
various  conditions  of  the  mind ;  for  in  all  these  cases  impres- 
sions must  be  conducted  to  and  fro  through  the  whole  distance 
between  the  part  and  the  spinal  cord  and  brain.  So,  also,  in 
experiments,  now  more  than  sufficiently  numerous,  irritations 
of  the  semiluuar  ganglia,  the  splanchnic  nerves,  the  thoracic, 
hepatic,  and  other  ganglia  and  nerves,  have  elicited  expres- 


450  THE    NERVOUS    SYSTEM. 

sions  of  pain,  and  have  excited  movements  in  the  muscular 
organs  supplied  from  the  irritated  part. 

In  the  case  of  pain  excited,  or  movements  affected  by  the 
mind,  it  may  be  supposed  that  the  conduction  of  impressions 
is  effected  through  the  cerebro-spinal  fibres  which  are  mingled 
in  all,  or  nearly  all,  parts  of  the  sympathetic  nerves.  There 
are  no  means  of  deciding  this ;  but  if  it  be  admitted  that  the 
conduction  is  effected  through  the  cerebro-spinal  nerve-fibres, 
then,  whether  or  not  they  pass  uninterruptedly  between  the 
brain  or  spinal  cord  and  the  part  affected,  it  must  be  assumed 
that  their  mode  of  conduction  is  modified  by  the  ganglia.  For, 
if  such  cerebro-spinal  fibres  are  conducted  in  the  ordinary 
manner,  the  parts  should  be  always  sensible  and  liable  to  the 
influence  of  the  will,  and  impressions  should  be  conveyed  to 
and  fro  instantaneously.  But  this  is  not  the  case  ;  on  the  con- 
trary, through  the  branches  of  the  sympathetic  nerve  and  its 
ganglia,  none  but  intense  impressions,  or  impressions  exagger- 
ated by  the  morbid  excitability  of  the  nerves  or  ganglia,  can 
be  conveyed. 

Respecting  the  general  action  of  the  ganglia  of  the  sympa- 
thetic nerve,  little  need  be  said  here,  since  they  may  be  taken 
as  examples  by  which  to  illustrate  the  common  modes  of  action 
of  all  nerve-centres  (see  p.  382).  Indeed,  complex  as  the  sym- 
pathetic system,  taken  as  a  whole,  is,  it  presents  in  each  of  its 
parts  a  simplicity  not  to  be  found  in  the  cerebro-spinal  system  : 
for  each  ganglion  with  afferent  and  efferent  nerves  forms  a 
simple  nervous  system,  and  might  serve  for  the  illustration  of 
all  the  nervous  actions  with  which  the  mind  is  unconnected. 
But  it  will  be  more  convenient  to  consider  the  ganglia  now  in 
connection  with  the  functions  that  they  may  be  supposed  to 
control,  in  the  several  organs  supplied  by  the  sympathetic  sys- 
tem alone,  or  in  conjunction  with  the  cerebro-spinal. 

The  general  processes  which  the  sympathetic  appears  to  in- 
fluence, are  those  of  involuntary  motion,  secretion,  and  nutri- 
tion. 

Many  movements  take  place  involuntarily  in  parts  supplied 
with  cerebro-spinal  nerves,  as  the  respiratory  and  other  spinal 
reflex  motions ;  but  the  parts  principally  supplied  with  sym- 
pathetic nerves  are  usually  capable  of  none  but  involuntary 
movements,  and  when  the  mind  acts  on  them  at  all,  it  is  only 
through  the  strong  excitement  or  depressing  influence  of  some 
passion,  or  through  some  voluntary  movement  with  which  the 
actions  of  the  involuntary  part  are  commonly  associated.  The 
heart,  stomach,  and  intestines  are  examples  of  these  state- 
ments ;  for  the  heart  and  stomach,  though  supplied  in  large 


THE     SYMPATHETIC     XERVE.  451 

measure  from  the  pneumogastric  nerves,  yet  probably  derive 
through  them  few  filaments  except  such  as  have  arisen  from 
their  ganglia,  and  are  therefore  of  the  nature  of  sympathetic 
fibres. 

The  parts  which  are  supplied  with  motor  power  by  the  sym- 
pathetic nerve  continue  to  move,  though  more  feebly  than  be- 
fore, when  they  are  separated  from  their  natural  connections 
with  the  rest  of  the  sympathetic  system,  and  wholly  removed 
from  the  body.  Thus,  the  heart,  after  it  is  taken  from  the 
body,  continues  to  beat  in  Mammalia  for  one  or  two  minutes, 
in  reptiles  and  Amphibia  for  hours ;  and  the  peristaltic  motions 
of  the  intestine  continue  under  the  same  circumstances.  Hence 
the  motion  of  the  parts  supplied  with  nerves  from  the  sympa- 
thetic are  shown  to  be,  in  a  measure,  independent  of  the  brain 
and  spinal  cord. 

It  seems  to  be  a  general  rule,  at  least  in  animals  that  have 
both  cerebro-spinal  and  sympathetic  nerves  much  developed, 
that  the  involuntary  movements  excited  by  stimuli  conveyed 
through  ganglia  are  orderly  and  like  natural  movements,  while 
those  excited  through  nerves  without  ganglia  are  convulsive 
and  disorderly ;  and  the  probability  is  that,  in  the  natural 
state,  it  is  through  the  same  ganglia  that  natural  stimuli,  im- 
pressing centripetal  nerves,  are  reflected  through  centrifugal 
nerves  to  the  involuntary  muscles.  As  the  muscles  of  respira- 
tion are  maintained  in  uniform  rhythmic  action  chiefly  by  the 
reflecting  and  combining  power  of  the  medulla  oblongata,  so, 
probably,  are  those  of  the  heart,  stomach,  and  intestines,  by 
their  several  ganglia.  And  as  with  the  ganglia  of  the  sympa- 
thetic and  their  nerves,  so  with  the  medulla  oblongata  and  its 
nerves  distributed  to  respiratory  muscles, — if  these  nerves  or 
the  medulla  oblougata  itself  be  directly  stimulated,  the  move- 
ments that  follow  are  convulsive  and  disorderly ;  but  if  the 
medulla  be  stimulated  through  a  centripetal  nerve,  as  when 
cold  is  applied  to  the  skin,  then  the  impressions  are  reflected 
so  as  to  produce  movements  which,  though  they  may  be  very 
quick  and  almost  convulsive,  are  yet  combined  in  the  plan  of 
the  proper  respiratory  acts. 

Among  the  ganglia  of  the  sympathetic  nerves  to  which  this 
co-ordination  of  movements  is  to  be  ascribed,  must  be  reckoned, 
not  those  alone  which  are  on  the  principal  trunks  and  branches 
of  the  sympathetic  external  to  any  organ,  but  those  also  which 
lie  in  the  very  substance  of  the  organs ;  such  as  those  dis- 
covered in  the  heart  by  Remak.  Those  also  may  be  included 
which  have  been  found  in  the  mesentery  close  by  the  intestines, 
as  well  as  in  the  submucous  tissue  of  the  stomach  and  intestinal 
canal  (Meissner),  and  in  other  parts.  The  extension  of  dis- 


452  THE     NERVOUS    SYSTEM. 

coveries  of  such  ganglia  will  probably  diminish  yet  further 
the  number  of  instances  in  which  the  involuntary  movements 
appear  to  be  effected  independently  of  central  nervous  in- 
fluence. 

Respecting  the  influence  of  the  sympathetic  nerve  in  nutri- 
tion and  secretion,  we  may  refer  to  the  chapters  on  those  pro- 
cesses. 

The  influence  of  the  sympathetic  nerves  on  the  bloodvessels 
has  been  already  referred  to  in  the  section  on  the  Arteries.  It 
was  stated  that  the  muscular  tissue  of  the  bloodvessels  was 
supplied  by  sympathetic  nerve-branches,  called  from  their  dis- 
tribution and  function  vaso-motor  nerves  ;  and  that  by  these  the 
condition  of  the  vessels  with  respect  to  contraction  or  relax- 
ation, and  therefore  to  the  stream  of  blood  which  flowed  through 
them  in  a  given  time,  is  governed.  When  these  vaso-motor 
nerves  are  intact,  the  muscular  tissue  of  the  arteries  is  always 
in  a  state  of  tonic  contraction,  which  varies  in  degree  at  dif- 
ferent times.  When  they  are  divided,  the  muscular  fibres  in 
which  they  are  distributed  are  paralyzed,  and  the  bloodvessels 
become  dilated.  The  most  usual  experiment  in  illustration  of 
these  facts  is  performed  by  exposing  in  a  rabbit  the  cervical 
sympathetic,  from  which  vaso-motor  branches  are  given  to  the 
bloodvessels  of  the  head  and  neck.  On  dividing  the  nerve,  the 
bloodvessels  of  the  same  side  are  paralyzed,  and  the  stream  of 
blood,  now  uncontrolled,  dilates  them.  The  effect  is  best  seen 
in  the  ear,  the  bloodvessels  of  which  become  manifestly  larger 
than  those  of  the  opposite  side ;  while  the  part  becomes  redder 
and  warmer  from  the  increased  quantity  of  blood  circulating 
through  it.  On  galvanizing  the  upper  divided  extremity  of 
the  nerve,  the  muscular  fibres  of  the  bloodvessels  respond  to 
the  stimulus  by  again  contracting,  and  the  parts  become  paler, 
colder,  and  less  sensitive  than  natural. 

The  vaso-motor  nerves  arise  directly  from  the  sympathetic. 
Thus  the  bloodvessels  of  the  head  and  neck  are  supplied  by 
branches  from  the  superior  cervical  ganglion,  those  of  the 
thorax  from  the  cervical  and  upper  dorsal  ganglia,  those  of 
the  abdomen  chiefly  by  the  splanchnic  nerves,  and  so  forth. 
But  it  is  now  generally  agreed,  from  the  results  of  experi- 
ments by  Ludwig  and  others,  that  the  principal  vaso-motor 
nerve-centre,  with  which  all  these  nerves  communicate,  and  by 
which  their  action  is  regulated,  is  situate  in  the  medulla  ob- 
longata — or,  in  other  words,  that  the  vaso-motor  fibres,  aris- 
ing from  this  nerve-centre,  pass  down  the  spinal  cord,  and 
issuing  by  the  anterior  roots  of  the  spinal  nerves,  enter  the 
various  ganglia  on  the  prsevertebral  cord  of  the  sympathetic, 
and  thence  reach  their  destination,  probably  taking  with  them 


THE    SYMPATHETIC    NERVE.  453 

fibres  which  arise  in  the  ganglia  through  which  they  pass. 
The  vaso-motor  centre  in  the  medulla  appears  to  have  a  regu- 
lating power  over  the  whole  of  the  vaso-motor  nerves  ;  but  it 
seems  likely  that  other  secondary  vaso-motor  centres  may 
exist  in  ganglia  in  different  parts  of  the  body,  and  may  be  the 
centres  by  which,  under  ordinary  circumstances,  vaso-motor 
changes  are  regulated  in  the  territory  in  which  they  are  placed. 

The  vaso-motor  nerve-centres  are  not  only  centres  from  which 
influences  are  directly  transmitted  to  the  bloodvessels,  but,  like 
other  nerve-centres,  may  be  the  means  by  which  impulses  are 
reflected  (p.  385).  And  reflex  actions  occur  in  connection  with 
the  muscular  fibres  of  bloodvessels,  as  with  those  of  the  vol- 
untary muscles.  Such  reflected  impressions  may  lead  either 
to  contraction  or  to  dilatation  of  bloodvessels ;  or,  in  other 
words,  the  action  may  be  excito-vaso-motor,  or  vaso-inhibitory. 
The  most  remarkable  instance  at  present  known  of  a  nerve, 
the  stimulation  of  which  leads  by  reflex  action  through  the 
vaso-motor  centre  in  the  medulla  oblongata,  to  dilatation  of 
bloodvessels,  is  the  depressor  branch  of  the  vagus  (p.  442) ; 
but  similar  effects  have  been  observed  in  a  less  degree,  on  stimu- 
lating other  afferent  spinal  nerves.1 

It  is,  of  course,  very  difficult  to  determine  the  relative  share 
exercised  by  the  true  sympathetic  and  the  ordinary  cerebro- 
spinal  fibres  in  the  contraction  of  bloodvessels,  and  in  the 
general  processes  of  nutrition  and  secretion,  since  both  kinds 
of  fibres  appear  to  be  distributed  to  most  parts,  and  there  seems 
to  be  no  possibility  of  isolating  them.  Probably  the  safest 
view  of  the  question  at  present  is,  still  to  regard  all  the  pro- 
cesses of  organic  life,  in  man,  as  liable  to  the  combined  influ- 
ences of  the  cerebro-spinal  and  the  sympathetic  systems ;  to 
consider  that  those  influences  may  be  so  combined  as  that  the 
sympathetic  nerves  and  ganglia  may  be  in  man,  as  in  the  lower 
animals,  the  parts  through  which  the  ordinary  and  constant 
influence  of  nervous  force  is  exercised  on  the  organic  processes ; 
while  the  cerebro-spinal  nervous  centres  and  their  ganglia  are 
so  closely  connected  with  the  proper  sympathetic  ganglia,  that 
neither  of  them  can  be  said  to  be  independent  of  the  other ; 
each,  as  a  rule,  and  under  ordinary  circumstances,  governing 
its  own  domain,  but  always  liable  to  be  influenced  by  the  other. 
_, » 

1  For  an  admirable  summary  of  what  is  at  present  known  regard- 
ing the  Innervation  of  the  Heart  and  Bloodvessels,  see  Lectures  by  Dr. 
Eutherford,  in  the  "  Lancet,"  December  16th,  1871,  and  January  20th, 
1872. 


454  MOTION. 


CHAPTER  XVII. 

CAUSES   AND   PHENOMENA    OF   MOTION. 

THE  most  evident  vital  motions  observable  in  the  bodies  of 
animals,  are  performed  in  one  or  other  of  the  following  ways : 
first,  by  means  of  the  oscillatory  motion  or  vibration  of  micro- 
scopic cilia,  with  which  the  surfaces  of  certain  membranes  are 
beset ;  and  secondly,  by  the  contraction  of  fibres  which  either 
have  a  longitudinal  direction  and  are  fixed  at  both  extremities, 
or  form  circular  bands ;  the  contraction  or  shortening  of  the 
fibres  bringing  the  parts  to  which  they  are  fixed  nearer  to  each 
other.  There  are,  besides,  various  molecular  movements  allied 
to  those  which  need  not  here  be  considered. 


CILIARY   MOTION. 

Ciliary  motion  consists  in  the  incessant  vibration  of  fine, 
pellucid,  blunt  processes,  about  ^^^  of  an  inch  long,  termed 
cilia  (Figs.  153,  154),  situated  on  the  free  extremities  of  the 
cells  of  epithelium  covering  certain  surfaces  of  the  body. 

The  distribution  and  structure  of  ciliary  epithelium  and  the 
microscopic  appearances  of  cilia  in  motion  have  been  already 
described  (p.  37). 

Ciliary  motion  seems  to  be  alike  independent  of  the  will,  of 
the  direct  influence  of  the  nervous  system,  and  of  muscular 
contraction,  for  it  is  involuntary ;  there  is  no  nervous  or  mus- 
cular tissue  in  the  immediate  neighborhood  of  the  cilia,  and 
it  continues  for  several  hours  after  death  or  removal  from  the 
body,  provided  the  portion  of  tissue  under  examination  be 
kept  moist.  Its  independence  of  the  nervous  system  is  shown 
also  in  its  occurrence  in  the  lowest  invertebrate  animals  appar- 
ently unprovided  with  anything  analogous  to  a  nervous  sys- 
tem, in  its  persistence  in  animals  killed  by  prussic  acid,  by 
narcotic  or  other  poisons,  and  after  the  direct  application  of 
narcotics  to  the  ciliary  surface,  or  the  discharge  of  a  Leyden 
jar,  or  of  a  galvanic  shock  through  it.  The  vapor  of  chloro- 
form arrests  the  motion ;  but  it  is  renewed  on  the  discontinu- 
ance of  the  application  (Lister).  According  to  Kuhne,  the 
movement  ceases  in  an  atmosphere  deprived  of  oxygen,  but  is 
revived  on  the  admission  of  this  gas.  Carbonic  acid  stops  the 


CILIARY     MOTION. 


455 


movement.  The  contact  of  various  substances  will  stop  the 
motion  altogether ;  but  this  seems  to  depend  chiefly  on  destruc- 
tion of  the  delicate  substance  of  which  the  cilia  are  composed. 


FIG.  153. 


FIG.  154. 


FIG.  153.— Spheroidal  ciliated  cells  from  the  mouth  of  the  frog;  magnified  300 
diameters  (Sharpey). 

FIG.  154.— Columnar  ciliated  epithelium  cells  from  the  human  nasal  membrane ; 
magnified  300  diameters  (Sharpey). 

Little  or  nothing  is  known  with  certainty  regarding  the  na- 
ture of  ciliary  action.  As  Dr.  Sharpey  observes,  however,  it 
is  a  special  manifestation  of  a  similar  property  to  that  by 
which  the  other  motions  of  animals  are  effected,  namely,  by 
what  we  term  vital  contractility.  The  fact  of  the  more  evident 
movements  of  the  larger  animals  being  effected  by  a  structure 
apparently  different  from  that  of  cilia,  is  no  argument  against 
such  a  supposition.  For,  if  we  consider  the  matter,  it  will  be 
plain  that  our  prejudices  against  admitting  a  relationship  to 
exist  between  the  two  structures,  muscles  and  cilia,  rests  on  no 
definite  ground  ;  and  for  the  simple  reason,  that  we  know  so 
little  of  the  manner  of  production  of  movement  in  either  case. 
The  mere  difference  of  structure  is  not  an  argument  in  point ; 
neither  is  the  presence  or  absence  of  nerves.  The  movements 
of  both  muscles  and  cilia  are  manifestations  of  force,  by  cer- 
tain special  structures,  which  we  call  respectively  muscles  and 
cilia.  We  know  nothing  more  about  the  means  by  which  the 
manifestation  is  effected  by  one  of  these  structures  than  by  the 
other ;  and  the  mere  fact  that  one  has  nerves  and  the  other 
has  not,  is  no  more  argument  against  cilia  having  what  we  call 
a  vital  power  of  contraction,  than  the  presence  or  absence  of 
stripes  from  voluntary  or  involuntary  muscles  respectively,  is 
an  argument  for  or  against  the  contraction  of  one  of  them 
being  vital  and  the  other  not  so.  Inasmuch  then  as  cilia  are 
found  in  living  structures  only,  and  inasmuch  as  they  are  a 
means  whereby  force  is  transformed  (see  Chap.  II),  their  pe- 
culiar properties  have  as  much  right  to  be  invested  with  the 
term  vital  as  have  those  of  muscular  fibres.  The  term  may  be 


456 


MOTION. 


in  both  instances  a  bad  one, — it  certainly  is  an  unsatisfactory 
one, — but  it  is  as  good  for  one  case  as  the  other. 


MUSCULAR    MOTION. 

There  are  two  chief  kinds  of  muscular  tissue,  the  striped, 
and  the  plain  or  unstriped,  and  they  are  distinguished  by  struc- 
tural peculiarities  and  mode  of  action.  The  striped  form  of 
muscular  fibre  is  sometimes  called  voluntary  muscle,  because 
all  muscles  under  the  control  of  the  will  are  constructed  of  it. 
The  plain  or  unstriped  variety  is  often  termed  involuntary,  be- 
cause it  alone  is  found  in  the  greater  number  of  the  muscles 
over  which  the  will  has  no  power. 

The  involuntary  or  unstriped  muscles  are  made  up,  accord- 
ing to  Kolliker,  of  elongated,  spindle-shaped,  nucleated  fibre- 
cells  (Fig.  155),  which  in  their  most  perfect  form  are  flat,  from 
about  ^^  to  -3-3^0  of  an  inch  broad,  and  about  g^0  to  8-Jn  of 
an  inch  in  length — very  clear,  granular,  and  brittle,  so  that 


FIG.  155. 


FIG. 156. 


FIG.  155.— Muscular  fibre-cells  from  human  arteries,  magnified  350  diameters 
(Kolliker).  a,  natural  state;  b,  treated  with  acetic  acid. 

FIG.  156.— Plain  muscular  fibres  from  the  human  bladder,  magnified  250  diameters, 
a,  in  their  natural  state  ;  6,  treated  with  acetic  acid  to  show  the  nuclei. 

when  they  break,  they  often  have  abruptly  rounded  or  square 
extremities.  Each  fibre-cell  possesses  an  elongated  nucleus, 
and  many  are  marked  along  the  middle,  or,  more  rarely,  along 


MUSCULAR    MOTION.  457 

one  of  the  edges,  either  by  a  fine  continuous  dark  streak,  or 
by  short  isolated  dark  lines,  or  by  dark  points  arranged  in  a 
row,  or  scattered.  These  fibre-cells,  by  their  union,  form  fibres 
and  bundles  of  fibres  (Fig.  156).  The  fibres  have  no  distinct 
sheath. 

The  fibres  of  involuntary  muscle,  such  as  are  here  described, 
form  the  proper  muscular  coats  of  the  digestive  canal  from 
the  middle  of  the  O3sophagus  to  the  internal  sphincter  ani,  of 
the  ureters  and  urinary  bladder,  the  trachea  and  bronchi,  the 
ducts  of  glands,  the  gall-bladder,  the  vesiculaB  seminales,  the 
pregnant  uterus,  of  bloodvessels  and  lymphatics,  the  iris,  and 
some  other  parts. 

This  form  of  tissue  also  enters  largely  into  the  composition 
of  the  tunica  dartos,  and  is  the  principal  cause  of  the  wrin- 
kling and  contraction  of  the  scrotum  on  exposure  to  cold.  The 
fibres  of  the  cremaster  assist  in  some  measure  in  producing 
this  effect,  but  they  are  chiefly  concerned  in  drawing  up  the 

FIG.  157. 


Perpendicular  section  through  the  scalp,  with  two  hair-sacs;  a,  epidermis;  6, 
cutis ;  c,  muscles  of  the  hair-follicles  (after  Kolliker). 

testis  and  its  coverings  towards  the  inguinal  opening.  Un- 
striped  muscular  tissue  occurs  largely  also  in  the  cutis  (p.  334), 
being  especially  abundant  at  the  interspaces  between  the  bases 
of  the  papillae.  Hence,  when  it  contracts  under  the  influence 
of  cold,  fear,  electricity,  or  any  other  stimulus,  the  papillae  are 
made  unusually  prominent,  and  give  rise  to  the  peculiar 
roughness  of  the  skin  termed  cutis  anserina,  or  goose-skin.  It 
occurs  also  in  the  superficial  portion  of  the  cutis,  in  all  parts 
where  hairs  occur,  in  the  form  of  flattened  roundish  bundles, 
which  lie  alongside  the  hair-follicles  and  sebaceous  glands. 
They  pass  obliquely  from  without  inwards,  embrace  the  seba- 
ceous glands,  and  are  attached  to  the  hair-follicles  near  their 
base  (Fig.  157). 


458  MOTION. 

To  this  kind  of  muscular  fibre  the  term  organic  is  often  ap- 
plied, from  the  fact  that  it  enters  especially  into  the  construc- 
tion of  such  parts  as  are  concerned  in  what  has  been  called 
organic  life  (see  note,  p.  368). 

The  muscles  of  animal  life,  or  striped  muscles,  include  the 
whole  class  of  voluntary  muscles,  the  heart,  and  those  muscles 

neither    completely    volun- 
FlG- 158-  tary  nor  involuntary,  which 

form  part  of  the  walls  of  the 
pharynx,  and  exist  in  many 
other  parts  of  the  body,  as 
the  internal  ear,  urethra, 
&c.  All  these  muscles  are 
composed  of  fleshy  bundles 
called  fasciculi,  inclosed  in 
coverings  of  fibro-cellular 
tissue,  by  which  each  is  at 
once  connected  with,  and 

A  small  portion  of  muscle   natural  sue,  igolated  from    thoge  adjacent 
consisting  of  larger  and  smaller  fasciculi,  /-n.          -txo\          17      r, 

seen  in  a  transverse  section,  and  the  same  to     lt     V*1*''.         .''.  .C 

magnified  5  diameters  (after  Sharpey).  bundle  is  again  divided  into 

smaller  ones,  similarly  en- 
sheathed  and  similarly  divisible ;  and  so  on,  through  an  un- 
certain number  of  gradations,  till  one  arrives  at  the  primitive 
fasciculi,  or  the  muscular  fibres  peculiarly  so  called. 

Muscular  fibres  consist,  each  of  them,  of  a  tube  or  sheath 
of  delicate,  structureless  membrane,  called  the  sarcolemma, 
inclosing  a  number  of  filaments  or  fibrils.  They  are  cylindri- 
form  or  prismatic,  with  five  or  more  sides,  according  to  the 
manner  in  which  they  are  compressed  by  adjacent  fibres. 
Their  average  diameter  is  about  -5^  of  an  inch,  and  their 
length  never  exceeds  an  inch  and  a  half. 

Each  muscular  fibre  is  thus  constructed :  Externally  is  a 
fine,  transparent,  structureless  membrane,  called  the  sarco- 
lemma, which  in  the  form  of  a  tubular  investing  sheath  forms 
the  outer  wall  of  the  fibre,  and  is  filled  by  the  contractile 
material  of  which  the  fibre  is  chiefly  made  up.  Sometimes, 
from  its  comparative  toughness,  the  sarcolemma  will  remain 
untorn,  when  by  extension  the  contained  part  can  be  broken 
(Fig.  159),  and  its  presence  is  in  this  way  best  demonstrated. 
The  fibres,  which  are  cylindriform  or  prismatic,  with  an  aver- 
age diameter  of  about  ^Q  of  an  inch,  are  of  a  pale  yellow 
color,  and  apparently  marked  by  fine  striae,  which  pass  trans- 
versely round  them,  in  slightly  curved  or  wholly  parallel 
lines.  Other,  but  generally  more  obscure  striae,  also  pass  lon- 
gitudinally over  the  tubes,  and  indicate  the  direction  of  the 


STRUCTURE    OF    STRIPED    MUSCLE.  459 

filaments  or  primitive  fibrils  of  which  the  substance  of  each 
fibre  is  composed  (Fig.  160). 

The  whole  substance  of  the  fibre  contained  within  the  sarco- 
lemma  may  be  thus  supposed  to  be  constructed  of  longitudinal 

FIG.  159.  FIG.  160. 


FIG.  159. — Muscular  fibre  torn  across ;  the  sarcolemma  still  connecting  the  two 
parts  of  the  fibre  (after  Todd  and  Bowman). 

FIG.  160.— A  few  muscular  fibres,  being  part  of  a  small  fasciculus,  highly  magni- 
fied, showing  the  transverse  striae,  a,  end  view  of  b,  b,  fibres ;  c,  a  fibre  split  into 
its  fibrils  (after  Sharpey). 

fibrils — a- bundle  of  fibrils  surrounded  by  the  sarcolemma  con- 
stituting a  fibre. 

There  is  still  some  doubt  regarding  the  nature  of  the  fibrils. 
Each  of  them  appears  to  be  composed  of  a  single  row  of  minute 
dark  quadrangular  particles  called  sarcous  elements,  which  are 
separated  from  each  other  by  a  bright  space  formed  of  a  pel- 
lucid substance  continuous  with  them.  A  fine  streak  can  be 
sometimes  discerned  passing  across  the  bright  interval  between 
the  sarcous  elements.  Dr.  Sharpey  believes  that,  even  in  a 
fibril  so  constituted,  the  ultimate  anatomical  element  of  the 
fibre  has  not  been  isolated.  He  believes  that  each  fibril  with 
quadrangular  sarcous  elements  is  composed  of  a  number  of 
other  fibrils  still  finer,  so  that  the  sarcous  element  of  an  ulti- 
mate fibril  would  be  not  quadrangular  but  as  a  streak,  and  the 
dark  transverse  streak  on  the  bright  space  but  a  row  of  dots. 
In  either  case  the  appearance  of  striation  in  the  whole  fibre 
would  be  produced  by  the  arrangement,  side  by  side,  of  the 
dark  and  light  portions  respectively  of  the  fibrils  (Fig.  161). 


460 


FIG.  162. 


A.  Portion  of  a  medium-sized  human  muscular  fibre,  magnified  nearly  800  diam- 
eters. B.  Separated  bundles  offilsrils  equally  magnified ;  a,  a,  larger,  and  6,  6,  smaller 
collections ;  c,  still  smaller ;  d,  d,  the  smallest  which  could  be  detached,  possibly  rep- 
resenting a  single  series  of  sarcous  elements  (after  Sharpey). 

Although  each  muscular  fibre  may  be  considered  to  be  formed 
of  a  number  of  longitudinal  fibrils,  ar- 
ranged side  by  side,  it  is  also  true  that  they 
are  not  naturally  separate  from  each  other, 
there  being  lateral  cohesion,  if  not  fusion, 
of  each  sarcous  element  with  those  around 
and  in  contact  with  it ;  so  that  it  happens 
that  there  is  a  tendency  for  a  fibre  to  split, 
not  only  into  separate  fibrils,  but  also  occa- 
sionally into  plates  or  disks,  each  of  which 
is  composed  of  sarcous  elements  laterally 
adherent  one  to  another. 

The   muscular  fibres   of  the   heart,  al- 
though   striped    and    resembling    closely 
those  of  the  voluntary  muscles   in   their 
Muscular  fibres  from     general  structure,  present  these  distinctions : 

the    heart    magnified,      rp,  fi  d  f  j    ^      striated 

showing    their    cross-  ',  J       .,, 

stria;,  divisions,  and  tne7  branch  and  anastomose  one  with  an- 
junctions  (from  KoiH-  other,  and  no  sarcolemma  can  be  usually 
ker).  discerned  (Fig.  162). 


PROPERTIES    OF     MUSCULAR    TISSUE.        461 

The  voluntary  muscles  are  freely  supplied  with  bloodves- 
sels ;  the  capillaries  form  a  network  with  oblong  meshes  around 
the  fibres  on  the  outside  of  the  sarcolemma.  No  vessels  pene- 
trate the  sarcolemma  to  enter  the  interior  of  the  fibre. 

Nerves  also  are  supplied  freely  to  muscles;  the  voluntary 
muscles  receiving  chiefly  nerves  from  the  cerebro-spinal  system, 
and  the  unstriped  muscles  from  the  sympathetic  or  ganglionic 
system. 

Properties  of  Muscular  Tissue. 

The  property  of  muscular  tissue,  by  which  its  peculiar 
functions  are  exercised,  is  its  contractility,  which,  in  the  con- 
traction or  shortening  of  muscle,  is  excited  by  all  kinds  of 
stimuli,  applied  either  directly  to  the  muscles,  or  indirectly  to 
them  through  the  medium  of  their  motor  nerves.  This  prop- 
erty, although  commonly  brought  into  action  through  the 
nervous  system,  is  inherent  in  the  muscular  tissue.  For — 1st, 
it  may  be  manifested  in  a  muscle  which  is  isolated  from  the 
influence  of  the  nervous  system  by  division  of  the  nerves  sup- 
plying it,  so  long  as  the  natural  tissue  of  the  muscle  is  duly 
nourished;  and  2dly,  it  is  manifest  in  a  portion  of  muscular 
fibre,  in  which,  under  the  microscope,  no  nerve-fibre  can  be 
traced. 

If  the  removal  of  nervous  influence  be  long  continued,  as 
by  division  of  the  nerve  supplying  a  muscle,  or  in  cases  of  paral- 
ysis of  long  standing,  the  irritability,  i.  e.,  the  power  of  both 
perceiving  and  responding  to  a  stimulus,  may  be  lost ;  but 
probably  this  is  chiefly  due  to  the  impaired  nutrition  of  the 
muscular  tissue,  which  ensues  through  its  inaction  (J.  Reid). 
The  irritability  of  muscles  is  also  of  course  soon  lost,  unless  a 
supply  of  arterial  blood  to  them  is  kept  up.  Thus,  after  liga- 
ture of  the  main  arterial  trunk  of  a  limb,  the  power  of  moving 
the  muscles  is  partially  or  wholly  lost,  until  the  collateral  cir- 
culation is  established;  and  when,  in  animals,  the  abdominal 
aorta  is  tied,  the  hind  legs  are  rendered  almost  powerless  (Se- 
galas).  So,  also,  it  is  to  the  imperfect  supply  of  arterial  blood 
to  tile  muscular  tissue  of  the  heart,  that  the  cessation  of  the 
action  of  this  organ  in  asphyxia  is  in  some  measure  due  (p. 
189).  ( 

Besides  the  property  of  contractility,  the  muscles,  especially 
the  striated  or  those  of  animal  life,  possess  sensibility  by  means 
of  the  sensitive  nerve-fibres  distributed  to  them.  The  amount 
of  common  sensibility  in  muscles  is  not  great;  for  they  may  be 
cut  or  pricked  without  giving  rise  to  severe  pain,  at  least  in 
their  healthy  condition.  But  they  have  a  peculiar  sensibility, 
or  at  least  a  peculiar  modification  of  common  sensibility,  which 

39 


462  MOTION. 

is  shown  in  that  their  nerves  can  communicate  to  the  mind  an 
accurate  knowledge  of  their  states  and  positions  when  in  action. 
By  this  sensibility,  we  are  not  only  made  conscious  of  the  mor- 
bid sensations  of  fatigue  and  cramp  in  muscles,  but  acquire, 
through  muscular  action,  a  knowledge  of  the  distance  of  bodies 
and  their  relation  to  each  other,  and  are  enabled  to  estimate 
and  compare  their  weight  and  resistance  by  the  effort  of  which 
we  are  conscious  in  measuring,  moving,  or  raising  them.  Ex- 
cept with  such  knowledge  of  the  position  and  state  of  each 
muscle,  we  could  not  tell  how  or  when  to  move  it  for  any  re- 
quired action ;  nor  without  such  a  sensation  of  effort  could  we 
maintain  the  muscles  in  contraction  for  any  prolonged  exer- 
tion. 

The  mode  of  contraction  in  the  transversely  striated  muscular 
tissue,  has  been  much  disputed.  The  most  probable  account, 
which  has  been  especially  illustrated  by  Mr.  Bowman,  is  that 
the  contraction  is  effected  by  an  approximation  of  the  constitu- 
ent parts  of  the  fibrils,  which,  at  the  instant  of  contraction, 
without  any  alteration  in  their  general  direction,  become  closer, 
flatter,  and  wider ;  a  condition  which  is  rendered  evident  by  the 
approximation  of  the  transverse  striae  seen  on  the  surface  of  the 
fasciculus,  and  by  its  increased  breadth  and  thickness.  The 
appearance  of  the  zigzag  lines  into  which  it  was  supposed  the 
fibres  are  thrown  in  contraction,  is  due  to  the  relaxation  of  a 
fibre  which  has  been  recently  contracted,  and  is  not  at  once 
stretched  again  by  some  antagonist  fibre,  or  whose  extremities 
are  kept  close  together  by  the  contractions  of  other  fibres. 
The  contraction  is  therefore  a  simple,  and  according  to  Ed. 
Weber,  a  uniform,  simultaneous,  and  steady  shortening  of 
each  fibre  and  its  contents.  What  each  fibril  or  fibre  loses  in 
length,  it  gains  in  thickness:  the  contraction  is  a  change  of 
form,  not  of  size ;  it  is,  therefore,  not  attended  with  any  dimi- 
nution in  bulk,  from  condensation  of  the  tissue.  This  has  been 
proved  for  entire  muscles,  by  making  a  mass  of  muscle,  or 
many  fibres  together,  contract  in  a  vessel  full  of  water,  with 
which  a  fine,  perpendicular,  graduated  tube  communicates. 
Any  diminution  of  the  bulk  of  the  contracting  muscle  would 
be  attended  by  a  fall  of  fluid  in  the  tube ;  but  when  the  ex- 
periment is  carefully  performed,  the  level  of  the  water  in  the 
tube  remains  the  same,  whether  the  muscle  be  contracted  or 
not.1 

In  thus  shortening,  muscles  appear  to  swell  up,  becoming 

1  Edward  Weber,  however,  states  that  a  very  slight  diminution 
does  take  place  in  the  bulk  of  a  contracting  muscle  ;  but  it  is  so  slight 
as  to  be  practical^  of  no  moment. 


SOUND    OF    MUSCULAR    CONTRACTION.      46& 

rounder,  more  prominent,  harder,  and  apparently  tougher. 
But  this  hardness  of  muscle  in  the  state  of  contraction,  is  not 
due  to  increased  firmness  or  condensation  of  the  muscular 
tissue,  but  to  the  increased  tension  to  which  the  fibres,  as  well 
as  their  tendons  and  other  tissues,  are  subjected  from  the  re- 
sistance ordinarily  opposed  to  their  contraction.  When  no 
resistance  is  offered,  as  when  a  muscle  is  cut  off  from  its  ten- 
don, not  only  is  no  hardness  perceived  during  contraction,  but 
the  muscular  tissue  is  even  softer,  more  extensile,  and  less 
elastic  than  in  its  ordinary  uncontracted  state  (Ed.  Weber). 

Heat  is  developed  in  the  contraction  of  muscles.  Becquerel 
and  Breschet  found,  with  the  thermo-multiplier,  about  1°  of 
heat  produced  by  each  forcible  contraction  of  a  man's  biceps ; 
and  when  the  actions  were  long  continued,  the  temperature  of 
the  muscle  increased  2°.  It  is  not  known  whether  this  devel- 
opment of  heat  is  due  to  chemical  changes  ensuing  in  the 
muscle,  or  to  the  friction  of  its  fibres  vigorously  acting :  in 
either  case,  we  may  refer  to  it  a  part  of  the  heat  developed  in 
active  exercise  (p.  190).  And  Nasse  suspects  that  to  it  is  due 
the  higher  temperature  of  the  blood  in  the  left  ventricle ;  for 
he  says  that  this  fluid  is  always  warmer  in  the  left  ventricle 
than  in  the  left  auricle,  and  that  the  blood  in  the  latter  is  but 
little  warmer  than  that  on  the  right  side  of  the  heart.  But 
these  experiments  need  confirmation. 

Sound  is  said  to  be  produced  when  muscles  contract  forcibly. 
Dr.  Wollaston  showed  that  this  sound  might  be  easily  heard 
by  placing  the  tip  of  the  little  finger  in  the  ear,  and  then 
making  some  muscles  contract,  as  those  of  the  ball  of  the 
thumb,  whose  sound  may  be  conducted  to  the  ear  through  the 
substance  of  the  hand  and  finger.  A  low  shaking  or  rum- 
bling sound  is  heard,  the  height  and  loudness  of  the  note  being 
in  direct  proportion  to  the  force  and  quickness  of  the  muscular 
action,  and  to  the  number  of  fibres  that  act  together,  or,  as  it 
were,  in  time. 

The  two  kinds  of  fibres,  the  striped  and  unstriped,  have 
characteristic  differences  in  the  mode  in  which  they  act  on  the 
application  of  the  same  stimulus ;  differences  which  may  be 
ascribed  in  great  part  to  their  respective  differences  of  struc- 
ture, but  to  some  degree  possibly,  to  their  respective  modes  of 
connection  with  the  nervous  system.  When  irritation  is  ap- 
plied directly  to  a  muscle  with  striated  fibres,  or  to  the  motor 
nerve  supplying  it,  contraction  of  the  part  irritated,  and  of 
that  only,  ensues ;  and  this  contraction  is  instantaneous,  and 
ceases  on  the  instant  of  withdrawing  the  irritation.  But 
when  any  part  with  unstriped  muscular  fibres,  e.  g.,  the  intes- 
tines or  bladder,  is  irritated,  the  subsequent  contraction  ensues 


464  MOTION. 

more  slowly,  extends  beyond  the  part  irritated,  and  with  alter- 
nating relaxation,  continues  for  some  time  after  the  withdrawal 
of  the  irritation.  Ed.  Weber  particularly  illustrated  the  dif- 
ference in  the  modes  of  contraction  of  the  two  kinds  of  mus- 
cular fibres  by  the  effects  of  the  electro-magnetic  stimulus. 
The  rapidly  succeeding  shocks  given  by  this  means  to  the 
nerves  of  muscles  excite  in  all  the  transversely-striated  muscles 
a  fixed  state  of  tetanic  contraction,  which  lasts  as  long  as  the 
stimulus  is  continued,  and  on  its  withdrawal  instantly  ceases : 
but  in  the  muscles  with  smooth  fibres  they  excite,  if  any  move- 
ment, only  one  that  ensues  slowly,  is  comparatively  slight, 
alternates  with  rest,  and  continues  for  a  time  after  the  stim- 
ulus is  withdrawn. 

In  their  mode  of  responding  to  these  stimuli,  all  the  volun- 
tary muscles,  or  those  with  transverse  striae,  are  alike;  but 
among  those  with  plain  or  unstriped  fibres  there  are  many  dif- 
ferences— a  fact  which  tends  to  confirm  the  opinion  that  their 
peculiarity  depends  as  well  on  their  connection  with  nerves 
and  ganglia  as  on  their  own  properties.  According  to  Weber, 
the  ureters  and  gall-bladder  are  the  parts  least  excited  by 
stimuli ;  they  do  not  act  at  all  till  the  stimulus  has  been  long 
applied,  aud  then  contract  feebly,  and  to  a  small  extent.  The 
contractions  of  the  caecum  and  stomach  are  quicker  and  wider- 
spread  ;  still  quicker  those  of  the  iris,  and  of  the  urinary 
bladder,  if  it  be  not  too  full.  The  actions  of  the  small  and 
large  intestines,  of  the  vas  deferens,  and  pregnant  uterus,  are 
yet  more  vivid,  more  regular,  and  more  sustained ;  and  they 
require  no  more  stimulus  than  that  of  the  air  to  excite  them. 
The  heart  is  the  quickest  and  most  vigorous  of  all  the  muscles 
of  organic  life  in  contracting  upon  irritation,  and  appears  in 
this  as  in  nearly  all  other  respects,  to  be  the  connecting  mem- 
ber of  the  two  classes  of  muscles. 

All  the  muscles  retain  their  property  of  contracting  under 
the  influence  of  stimuli  applied  to  them  or  to  their  nerves  for 
some  time  after  death,  the  period  being  longer  in  cold-blooded 
than  in  warm-blooded  Vertebrata,  and  shorter  in  birds  than 
in  Mammalia.  It  would  seem  as  if  the  more  active  the  respi- 
ratory process  in  the  living  animal,  the  shorter  is  the  time  of 
duration  of  the  irritability  in  the  muscles  after  death ;  and 
this  is  confirmed  by  the  comparison  of  different  species  in  the 
same  order  of  Vertebrata.  But  the  period  during  which  this 
irritability  lasts,  is  not  the  same  in  all  persons,  nor  in  all  the 
muscles  of  the  same  persons.  In  a  man  it  ceases,  according 
to  Nysten,  in  the  following  order :  First  in  the  left  ventricle, 
then  in  the  intestines  and  stomach,  the  urinary  bladder,  right 
ventricle,  oesophagus,  iris ;  then  in  the  voluntary  muscles  of  the 


EIGOR    MORTIS.  465 

trunk,  lower  and  upper  extremities  ;  lastly  in  the  right  and 
left  auricle  of  the  heart. 

After  the  muscles  of  the  dead  body  have  lost  their  irrita- 
bility or  capability  of  being  excited  to  contraction  by  the  ap- 
plication of  a  stimulus,  they  spontaneously  pass  into  a  state  of 
contraction,  apparently  identical  with  that  which  ensues  during 
life.1  It  affects  all  the  muscles  of  the  body  ;  and,  where  ex- 
ternal circumstances  do  not  prevent  it,  commonly  fixes  the 
limbs  in  that  which  is  their  natural  posture  of  equilibrium  or 
rest.  Hence,  and  from  the  simultaneous  contraction  of  all  the 
muscles  of  the  trunk,  is  produced  a  general  stiffening  of  the 
body,  constituting  the  rigor  mortis  or  post-mortem  rigidity} 

The  muscles  are  not  affected  exactly  simultaneously  by  the 
post-mortem  contraction,  but  rather  in  succession.  It  affects 
the  neck  and  lower  jaw  first ;  next,  the  upper  extremities,  ex- 
tending from  above  downwards  ;  and  lastly,  reaches  the  lower 
limbs  ;  in  some  rare  instances  only,  it  affects  the  lower  ex- 
tremities before,  or  simultaneously  with,  the  upper  extremities. 
It  usually  ceases  in  the  order  in  which  it  began ;  first  at  the 
head,  then  in  the  upper  extremities,  and  lastly  in  the  lower 
extremities.  According  to  Sommer,  it  never  commences 
earlier  than  ten  minutes,  and  never  later  than  seven  hours, 
after  death  ;  and  its  duration  is  greater  in  proportion  to  the 
lateness  of  its  accession.  According  to  Schiffer,  and  others 
have  confirmed  the  truth  of  his  observation,  heat  is  developed 
during  the  passage  of  a  muscular  fibre  into  the  condition  of 
rigor  mortis. 

Since  rigidity  does  not  ensue  until  muscles  have  lost  the  ca- 
pacity of  being  excited  by  external  stimuli,  it  follows  that  all 
circumstances  which  cause  a  speedy  exhaustion  of  muscular 
irritability,  induce  an  early  occurrence  of  the  rigidity,  while 
conditions  by  which  the  disappearance  of  the  irritability  is 
delayed,  are  succeeded  by  a  tardy  onset  of  this  rigidity. 
Hence  its  speedy  occurrence,  and  equally  speedy  departure  in 

1  If,   however,   arterial   blood  be  made  to  circulate  through   the 
body  or  through  a  limb,  the  post-mortem  contraction  of  the  muscles 
thus  supplied  with  blood,  may,  as  Dr.  Brown-Sequard  has  shown,  be 
suspended,  and  the  muscles  again  admit  of  contracting  on  the  appli- 
cation of  a  stimulus. 

2  It  should  be  stated  here,  however,  that  the  generally  accepted  ex- 
planation  of  the  state  of  the  muscles  during  rigor  mortis,  namely, 
that  it  is  due  to  contraction  of  the  fibres,  as  in  strong  action  during 
life,  is  denied  by  some  physiologists,  who  maintain  that  the  condition 
of  the  muscles  is  not  due  to  contraction  at  all,  but  is  caused  by  a  kind 
of  coagulation   of   the  interfibrillar  juices      This  idea   has  been  of 
late  especially  supported  by  Dr.  Norris  (see  Camb.  Journal  of  Anat- 
omy and  Physiology,  Part  I). 


466  MOTION. 

the  bodies  of  persons  exhausted  by  chronic  diseases ;  and  its 
tardy  onset  and  long  continuance  after  sudden  death  from 
acute  diseases.  In  some  cases  of  sudden  death  from  lightning, 
violent  injuries,  or  paroxysms  of  passion,  rigor  mortis  has  been 
said  not  to  occur  at  all ;  but  this  is  not  always  the  case.  It 
may,  indeed,  be  doubted  whether  there  is  really  a  complete 
absence  of  the  post-mortem  rigidity  in  any  such  cases ;  for  the 
experiments  of  M.  Brown-Sequard  with  electro-magnetism 
make  it  probable  that  the  rigidity  may  supervene  immediately 
after  death,  and  then  pass  away  with  such  rapidity  as  to  be 
scarcely  observable.  Thus,  he  took  five  rabbits,  and  killed 
them  by  removing  their  hearts.  In  the  first,  rigidity  came  on 
in  ten  hours,  and  lasted  192  hours ;  in  the  second,  which  was 
feebly  electrified,  it  commenced  in  seven  hours,  and  lasted  144; 
in  the  third,  which  was  more  strongly  electrified,  it  came  on 
in  two,  and  lasted  72  hours ;  in  the  fourth,  which  was  still 
more  strongly  electrified,  it  came  on  in  one  hour,  and  lasted  20 ; 
while,  in  the  last  rabbit,  which  was  submitted  to  a  powerful 
electro-galvanic  current,  the  rigidity  ensued  in  seven  minutes 
after  death,  and  passed  away  in  25  minutes.  From  this  it 
appears  that  the  more  powerful  the  electric  current,  the  sooner 
does  the  rigidity  ensue,  and  the  shorter  is  its  duration ;  and  as 
the  lightning  shock  is  so  much  more  powerful  than  any  ordi- 
nary electric  discharge,  the  rigidity  may  ensue  so  early  after 
death  and  pass  away  so  rapidly  as  to  escape  detection.  The 
influence  exercised  upon  the  onset  and  duration  of  post-mortem 
rigidity  by  causes  which  exhaust  the  irritability  of  the  mus- 
cles, was  well  illustrated  in  further  experiments  by  the  same 
physiologist,  in  which  he  found  that  the  rigor  mortis  ensued 
far  more  rapidly  and  lasted  for  a  shorter  period  in  those  mus- 
cles which  had  been  powerfully  electrified  just  before  death 
than  in  those  which  had  not  been  thus  acted  upon. 

The  occurrence  of  rigor  mortis  is  not  prevented  by  the  pre- 
vious existence  of  paralysis  in  a  part,  provided  the  paralysis 
has  not  been  attended  with  very  imperfect  nutrition  of  the 
muscular  tissue. 

The  rigidity  affects  the  involuntary  as  well  as  the  voluntary 
muscles,  whether  they  be  constructed  of  striped  or  unstriped 
fibres.  The  rigidity  of  involuntary  muscles  with  striped  fibres 
is  shown  in  the  contraction  of  the  heart  after  death.  The  con- 
traction of  the  muscles  with  unstriped  fibres  is  shown  by  an 
experiment  of  Valentin,  who  found  that  if  a  graduated  tube 
connected  with  a  portion  of  intestine  taken  from  a  recently- 
slain  animal,  be  filled  with  water,  and  tied  at  the  opposite 
end,  the  water  will  in  a  few  hours  rise  to  a  considerable  height 
in  the  tube,  owing  to  the  contraction  of  the  intestinal  walls. 


ACTIONS    OF    VOLUNTAEY     MUSCLES.        467 

It  is  still  better  shown  in  the  arteries,  of  which  all  that  have 
muscular  coats  contract  after  death,  and  thus  present  the 
roundness  and  cord-like  feel  of  the  arteries  of  a  limb  lately  re- 
moved, or  those  of  a  body  recently  dead.  Subsequently  they 
relax,  as  do  all  the  other  muscles,  and  feel  lax  and  flabby,  and 
lie  as  if  flattened,  and  with  their  walls  nearly  in  contact.1 


Actions  of  the  Voluntary  Muscles. 

The  greater  part  of  the  voluntary  muscles  of  the  body  act 
as  sources  of  power  for  moving  levers, — the  latter  consisting 
of  the  various  bones  to  which  the  muscles  are  attached. 

All  levers  have  been  divided  into  three  kinds,  according  to 
the  relative  position  of  the  power,  the  weight  to  be  moved,  and 
the  axis  of  motion  or  fulcrum.  In  a  lever  of  the  first  kind  the 
power  is  at  one  extremity  of  the  lever,  the  weight  at  the  other, 
and  the  fulcrum  between  the  two.  If  the  initial  letters  only 
of  the  power,  weight,  and  fulcrum  be  used,  the  arrangement 
will  stand  thus:  P.F.W.  A  poker,  as  ordinarily  used,  or 
the  bar  in  Fig.  164,  may  be  cited  as  an  example  of  this  variety 
of  lever ;  while  as  an  instance  in  which  the  bones  of  the  human 
skeleton  are  used  as  a  lever  of  the  same  kind,  may  be  men- 
tioned the  act  of  raising  the  body  from  the  stooping  posture 
by  means  of  the  hamstring  muscles  attached  to  the  tuberosity 
of  the  ischium  (Fig.  163). 

In  a  lever  of  the  second  kind,  the  arrangement  is  thus : 
P.W.F. ;  and  this  leverage  is  employed  in  the  act  of  raising 
the  handles  of  a  wheelbarrow,  or  in  stretching  an  elastic  band, 
as  in  Fig.  164.  In  the  human  body  the  act  of  opening  the 

1  Although  the  preceding  remarks  represent  the  views  generally 
entertained  in  regard  to  muscular  action,  yet  it  must  be  observed 
that  a  new  and  very  different  theory  on  the  subject  has  been  lately 
advanced  by  several  writers,  and  especially  developed  by  Dr.  Rad- 
cliffe,  who  has  also  made  it  the  basis  of  new  views  on  the  pathology  of 
various  convulsive  affections.  According  to  this  doctrine,  the  ordi- 
nary relaxed  or  elongated  state  of  a  muscle  is  due  to  a  certain  "  state 
of  polarity"  in  which  the  muscle  is  maintained,  and  contraction  is 
brought  about  by  anything  (such  as  an  effort  of  the  will)  which  lib- 
erates the  muscle  from  this  influence,  and  thus  leaves  it  to  the  opera- 
tion of  the  attractive  force  inherent  in  the  muscular  molecules.  Ac- 
cording to  this  doctrine,  also,  the  stage  of  rigor  mortis  is  readily 
explicable :  death  depriving  the  muscles  of  the  "  state  of  polarity'" 
whereby  they  had  hitherto  been  kept  relaxed,  and  thus  allowing  the 
attractive  force  of  the  muscular  particles  to  come  into  play.  For 
facts  and  arguments  in  support  of  this  view,  and  for  references  and 
confirmatory  opinions,  Dr.  Radcliffe's  work  on  epileptic  and  other 
convulsive  affections  may  be  consulted. 


468 


M  O  T I O  N. 


mouth  by  depressing  the  lower  jaw,  is  an  example  of  the  same 
kind, — the  tension  of  the  muscles  which  close  the  jaw  repre- 
senting the  weight  (Fig.  164). 


In  a  lever  of  the  third  kind  the  arrangement  is — F.P.W., 
and  the  act  of  raising  a  pole,  as  in  Fig.  165,  is  an  example. 
In  the  human  body  there  are  numerous  examples  of  the  em- 


ployment of  this  kind  of  leverage.     The  act  of  bending  the 
forearm  may  be  mentioned  as  an  instance  (Fig.  165). 

In  the  human  body,  levers  are  most  frequently  used  at  a 
disadvantage  as  regards  power,  the  latter  being  sacrificed  for 
the  sake  of  a  greater  range  of  motion.  Thus  in  the  diagrams 
of  the  first  and  third  kinds  it  is  evident  that  the  power  is  so 
close  to  the  fulcrum,  that  great  force  must  be  exercised  in  order 


VARIETIES    OF    LEVERS. 


469 


to  produce  motion.  It  is  also  evident,  however,  from  the  same 
diagrams,  that  by  the  closeness  of  the  power  to  the  fulcrum  a 
great  range  of  movement  can  be  obtained  by  means  of  a  com- 
paratively slight  shortening  of  the  muscular  fibres. 


FIG. 165. 


The  greater  number  of  the  more  important  muscular  actions 
of  the  human  body — those,  namely,  which  are  arranged  har- 
moniously so  as  to  subserve  some  definite  purpose  or  other  in 
the  animal  economy — are  described  in  various  parts  of  this 
work,  in  the  sections  which  treat  of  the  physiology  of  the  pro- 
cesses by  which  these  muscular  actions  are  resisted  or  carried 
out.  The  combined  action  of  the  respiratory  muscles,  for  in- 
stance, will  be  found  described  in  the  chapter  on  "  Respira- 
tion ;"  the  action  of  the  heart  and  bloodvessels,  under  the 
head  of  "  Circulation  ;"  while  the  movements  of  the  stomach 
and  intestines  are  too  intimately  associated  with  the  function 
of  "  Digestion,"  to  be  described  apart  from  it.  There  are, 
however,  one  or  two  very  important  and  somewhat  complicated 
muscular  acts  which  may  be  best  described  in  this  place. 

Walking. — In  the  act  of  walking,  almost  every  voluntary 
muscle  in  the  body  is  brought  into  play,  either  directly  for 
purposes  of  progression,  or  indirectly  for  the  proper  balancing 
of  the  head  and  trunk.  The  muscles  of  the  arms  are  least 
concerned ;  but  even  these  are  for  the  most  part  instinctively 
in  action  also  to  some  extent. 

Among  the  chief  muscles  engaged  directly  in  the  act  of 
walking  are  those  of  the  calf,  which,  by  pulling  up  the  heel, 
pull  up  also  the  astragalus,  and  with  it,  of  course,  the  whole 
body,  the  weight  of  which  is  transmitted  through  the  tibia  to 
this  bone  (Fig.  166).  When  starting  to  walk,  say  with  the 
left  leg,  this  raising  of  the  body  is  not  left  entirely  to  the 
muscles  of  the  left  calf,  but  the  trunk  is  thrown  forward  in 

40 


470  MOTION. 

such  a  way  that  it  would  fall  prostrate  were  it  Dot  that  the 
right  foot  is  brought  forward  and  planted  on  the  ground  to 
support  it.  Thus  the  muscles  of  the  left  calf  are  assisted  in 
their  action  by  those  muscles  on  the  front  of  the  trunk  and 
legs  which,  by  their  contraction,  pull  the  body  forwards ;  and 
of  course,  if  the  trunk  form  a  slanting  line,  with  the  inclina- 

FlG.  166. 


tion  forwards,  it  is  plain  that  when  the  heel  is  raised  by  the 
calf-muscles,  the  whole  body  will  be  raised,  and  pushed  ob- 
liquely forwards  and  upwards.  The  successive  acts  in  taking 
the  first  step  in  walking  are  represented  in  Fig.  166,  1,  2,  3. 

Now  it  is  evident  that  by  the  time  the  body  has  assumed 
the  position  No.  3,  it  is  time  that  the  right  leg  should  be 
brought  forward  to  support  it  and  prevent  it  from  falling  pros- 
trate. This  advance  of  the  other  leg  (in  this  case  the  righfy 
is  effected  partly  by  its  mechanically  swinging  forwards,  pen- 
dulum-wise, and  partly  by  muscular  action ;  the  muscles  used 
being, — 1st,  those  on  the  front  of  the  thigh,  which  bend  the 
thigh  forwards  on  the  pelvis,  especially  the  rectus  femoris,  with 
the  psoas  and  the  iliacus ;  2dly,  the  hamstring  muscles,  which 
slightly  bend  the  leg  on  the  thigh  ;  and  3dly,  the  muscles  on 
the  front  of  the  leg,  which  raise  the  front  of  the  foot  and  toes, 
and  so  prevent  the  latter  in  swinging  forwards  from  hitching 
in  the  ground.  Anybody  who  has  attentively  watched  the 
helpless  flapping  action  of  the  foot  and  leg  in  cases  of  partial 
paralysis  affecting  the  muscles  of  the  leg,  or  who  will,  in  his 
own  case,  note  the  act  of  bringing  the  leg  forward  in  walking, 
will  be  convinced  of  the  large  share  which  the  muscles  take 
in  the  act  in  question  ;  although,  of  course,  their  work  is  ren- 
dered much  easier  by  the  pendulum-like  swinging  forward  of 
the  leg  by  its  own  weight. 

The  second  part  of  the  act  of  walking,  which  has  been  just 
described,  is  shown  in  the  diagram  (4,  Fig.  166). 

When  the  right  foot  has  reached  the  ground  the  action  of 


WALKING.  471 

the  left  leg  has  not  ceased.  The  calf-muscles  of  the  latter  con- 
tinue to  act,  and  by  pulling  up  the  heel,  throw  the  body  still 
more  forwards  over  the  right  leg,  now  bearing  nearly  the  whole 
weight,  until  it  is  time  that  in  its  turn  the  left  leg  should  swing 
forwards,  and  the  left  foot  be  planted  on  the  ground  to  prevent 
the  body  from  falling  prostrate.  As  at  first,  while  the  calf- 
muscles  of  one  leg  and  foot  are  preparing,  so  to  speak,  to  push 
the  body  forward  and  upward  from  behind  by  raising  the  heel, 
the  muscles  on  the/r0?^of  the  trunk  and  of  the  same  leg  (and 
of  the  other  leg,  except  when  it  is  swinging  forwards)  are 
helping  the  act  by  pulling  the  legs  and  trunk,  so  as  to  make 
them  incline  forward,  the  rotation  in  the  inclining  forwards 
being  effected  mainly  at  the  ankle-joint.  Two  main  kinds  of 
leverage  are,  therefore,  employed  in  the  act  of  walking,  and  if 
this  idea  be  firmly  grasped,  the  detail  will  be  understood  with 
comparative  ease.  One  kind  of  leverage  employed  in  walking 
is  essentially  the  same  with  that  employed  in  pulling  forward 
the  pole,  as"  in  Fig.  165.  And  the  other,  less  exactly,  is  that 
employed  in  raising  the  handles  of  a  wheelbarrow.  Now,  sup- 
posing the  lower  end  of  the  pole  to  be  placed  in  the  barrow, 
we  should  have  a  very  rough  and  inelegant,  but  not  altogether 
bad  representation  of  the  two  main  levers  employed  in  the  act 
of  walking.  The  body  is  pulled  forward  by  the  muscles  in 
front,  much  in  the  same  way  that  the  pole  might  be  by  the 
force  applied  at  P,  Fig.  165,  while  the  raising  of  the  heel  and 
pushing  forwards  of  the  trunk  by  the  calf-muscles  is  roughly 
represented  on  raising  the  handles  of  the  barrow.  The  man- 
ner in  which  these  actions  are  performed  alternately  by  each 
leg,  so  that  one  after  the  other  is  swung  forwards  to  support 
the  trunk,  which  is  at  the  same  time  pushed  and  pulled  for- 
wards by  the  muscles  of  the  other,  may  be  gathered  from  the 
previous  description. 

There  is  one  more  thing  to  be  noticed  especially  in  the  act 
of  walking.  Inasmuch  as  the  body  is  being  constantly  sup- 
ported and  balanced  on  each  leg  alternately,  and  therefore  on 
only  one  at  the  same  moment,  it  is  evident  that  there  must  be 
some  provision  made  for  throwing  the  centre  of  gravity  over 
the  line  of  support  formed  by  the  bones  of  each  leg,  as,  in  its 
turn,  it  supports  the  weight  of  the  body.  This  may  be  done 
in  various  ways,  and  the  manner  in  which  it  is  effected  is  one 
element  in  the  differences  which  exist  in  the  walking  of  differ- 
ent people.  Thus  it  may  be  done  by  an  instinctive  slight  ro- 
tation of  the  pelvis  on  the  head  of  each  femur  in  turn,  in  such 
a  manner  that  the  centre  of  gravity  of  the  body  shall  fall  over 
the  foot  of  this  side.  Thus  when  the  body  is  pushed  onwards 
and  upwards  by  the  raising,  say,  of  the  right  heel,  as  in  Fig. 


472  MOTION. 

166,  3,  the  pelvis  is  instinctively,  by  various  muscles,  made  to 
rotate  on  the  head  of  the  left  fernur  at  the  acetabulum,  to  the 
left  side,  so  that  the  weight  may  fall  over  the  line  of  support 
formed  by  the  left  leg  at  the  time  that  the  right  leg  is  swing- 
ing forwards,  and  leaving  all  the  work  of  support  to  fall  on 
its  fellow.  Such  a  "  rocking "  movement  of  the  trunk  and 
pelvis,  however,  is  but  an  awkward  manner  of  doing  what  can 
be  done  more  gracefully  by  combining  a  slight  "  rocking"  with 
a  movement  of  the  whole  trunk  and  leg  over  the  foot  which 
is  being  planted  on  the  ground  (Fig.  167);  the  action  being 

FIG.  167. 


accompanied  with  a  compensatory  outward  movement  at  the 
hip,  more  easily  appreciated  by  looking  at  the  figure  (167) 
than  described. 

Thus  the  body  in  walking  is  continually  rising  and  swaying 
alternately  from  one  side  to  the  other,  as  its  centre  of  gravity 
has  to  be  brought  alternately  over  one  or  other  leg ;  and  the 
curvatures  of  the  spine  are  altered  in  correspondence  with  the 
varying  position  of  the  weight  which  it  has  to  support.  The 
extent  to  which  the  body  is  raised  or  swayed  differs  much  in 
different  people. 

In  walking,  one  foot  or  the  other  is  always  on  the  ground. 
The  act  of  leaping,  or  jumping,  consists  in  so  sudden  a  raising 
of  the  heels  by  the  sharp  and  strong  contraction  of  the  calf- 


SOURCE    OF    MUSCULAR    ACTION.  473 

muscles,  that  the  body  is  jerked  off  the  ground.  At  the  same 
time  the  effect  is  much  increased  by  first  bending  the  thighs 
on  the  pelvis,  and  the  legs  on  the  thighs,  and  then  suddenly 
straightening  out  the  angles  thus  formed.  The  share  which 
this  action  has  in  producing  the  effect  may  be  easily  known  by 
attempting  to  leap  in  the  upright  posture,  with  the  legs  quite 
straight. 

Running  is  performed  by  a  series  of  rapid  low  jumps  with 
each  leg  alternately ;  so  that,  during  each  complete  muscular 
act  concerned,  there  is  a  moment  when  both  feet  are  off  the 
ground. 

In  all  these  cases,  however,  the  description  of  the  manner 
in  which  any  given  effect  is  produced,  can  give  but  a  very  im- 
perfect idea  of  the  infinite  number  of  combined  and  harmoni- 
ously arranged  muscular  contractions  which  are  necessary  for 
even  the  simplest  acts  of  locomotion. 

Actions  of  the  Involuntary  Muscles. — The  involuntary  mus- 
cles are  for  the  most  part  not  attached  to  bones  arranged  to 
act  as  levers,  but  enter  into  the  formation  of  such  hollow  parts 
as  require  a  diminution  of  their  calibre  by  muscular  action, 
under  particular  circumstances.  Examples  of  this  action  are 
to  be  found  in  the  intestines,  urinary  bladder,  heart  and  blood- 
vessels, gall-bladder,  gland-ducts,  &c. 

The  difference  in  the  manner  of  contraction  of  the  striated 
and  non-striated  fibres  has  been  already  referred  to  (p.  463) ; 
and  the  peculiar  vermicular  or  peristaltic  action  of  the  latter 
fibres  in  some  regions  of  the  body  has  been  described  at  p.  276. 

Source  of  Muscular  Action. 

It  was  formerly  supposed  that  each  act  of  contraction  on 
the  part  of  a  muscle  was  accompanied  by  a  correlative  waste 
or  destruction  of  its  own  substance ;  and  that  the  quantity  of 
the  nitrogenous  excreta,  especially  of  urea,  presumably  the  ex- 
pression of  this  waste,  was  in  exact  proportion  to  the  amount 
of  muscular  work  performed.  It  has  been  found,  however, 
both  that  the  theory  itself  is  erroneous,  and  that  the  supposed 
facts  on  which  it  was  founded  do  not  exist. 

It  is  true  that  in  the  action  of  muscles,  as  of  all  other  parts, 
there  is  a  certain  destruction  of  tissue  or,  in  other  words,  a 
certain  "wear  and  tear,"  which  may  be  represented  by  a  slight 
increase  in  the  quantity  of  urea  excreted :  but  it  is  not  the 
cor  relative  expression  or  only  source  of  the  power  manifested. 
The  increase  in  the  amount  of  urea  which  is  excreted  after 
muscular  exertion  is  by  no  means  so  great  as  was  formerly 
supposed  ;  indeed,  it  is  very  slight.  And  as  there  is  no  reason 


474  VOICE    AND    SPEECH. 

to  believe  that  the  waste  of  muscle-substance  can  be  expressed, 
with  unimportant  exceptions,  in  any  other  way  than  by  an 
increased  excretion  of  urea,  it  is  evident  that  we  must  look 
elsewhere  than  in  destruction  of  muscle,  for  the  source  of 
muscular  action.  For,  it  need  scarcely  be  said,  all  force 
manifested  in  the  living  body  must  be  the  correlative  expres- 
sion of  force  previously  latent  in  the  food  eaten  or  the  tissue 
formed ;  and  evidences  of  force  expended  in  the  body  must  be 
found  in  the  excreta.  If,  therefore,  the  nitrogenous  excreta, 
represented  chiefly  by  urea,  are  not  in  sufficient  quantity  to 
account  for  the  work  done,  we  must  look  to  the  non-nitrogenous 
excreta  as  carbonic  acid  and  water,  which  presumably,  cannot 
be  the  expression  of  wasted  muscle-substance. 

The  quantity  of  these  non-nitrogenous  excreta  is  undoubtedly 
increased  by  active  muscular  efforts,  and  to  a  considerable 
extent ;  and  whatever  may  be  the  source  of  the  water,  the  car- 
bonic acid,  at  least,  is  the  result  of  chemical  action  in  the 
system,  and  especially  of  the  combustion  of  non-nitrogenous 
food,  although,  doubtless,  of  nitrogenous  food  also.  We  are, 
therefore,  driven  to  the  conclusion, — that  the  substance  of 
muscles  is  not  wasted  in  proportion  to  the  work  they  perform  ; 
and  that  the  non-nitrogenous  as  well  as  the  nitrogenous  foods 
may,  in  their  combustion,  afford  the  requisite  conditions  for 
muscular  action.  The  urgent  necessity  for  nitrogenous  food, 
especially  after  exercise,  is  probably  due  more  to  the  need  of 
nutrition  by  the  exhausted  muscles  and  other  tissues  for  which, 
of  course,  nitrogen  is  essential,  than  to  such  food  being  superior 
to  non-nitrogenous  substances  as  a  source  of  muscular  power. 


CHAPTER  XVIII. 

OF   VOICE    AND   SPEECH. 

IN  nearly  all  air-breathing  vertebrate  animals  there  are 
arrangements  for  the  production  of  sound,  or  voice,  in  some 
part  of  the  respiratory  apparatus.  In  many  animals  the  sound 
admits  of  being  variously  modified  and  altered  during  and 
after  its .  production ;  and,  in  man,  one  of  the  results  of  such 
modification  is  speech. 

Mode  of  Production  of  the  Human  Voice. 
It  has  been  proved  by  observations  on  living  subjects,  by 


VOICE     AND    SPEECH. 


475 


means  of  the  laryngoscope,  as  well  as  by  experiments  on  the 
larynx  taken  from  the  dead  body,  that  the  sound  of  the  human 
voice  is  the  result  of  the  inferior  laryngeal  ligaments,  or  true 
vocal  cords  (A,  cv,  Fig.  172)  which  bound  the  glottis,  being 


FIG.  168. 


Outline  showing  the  general  form  of  the  larynx,  trachea,  and  bronchi,  as  seen 
from  before.  %. — h,  the  great  cornu  of  the  hyoid  bone ;  e,  epiglottis  ;  t,  superior,  and 
/',  inferior  cornu  of  the  thyroid  cartilage  ;  c,  middle  of  the  cricoid  cartilage  ;  tr,  the 
trachea,  showing  sixteen  cartilaginous  rings  ;  ft,  the  right,  and  b',  the  left  bronchus. 

thrown  into  vibration  by  currents  of  expired  air  impelled  over 
their  edges.     Thus,  if  a  free  opening  exists  in  the  trachea,  the 


476  VOICE    AND    SPEECH. 

sound  of  the  voice  ceases,  but  returns  on  the  opening  being 
closed.  An  opening  into  the  air-passages  above  the  glottis,  on 
the  contrary,  does  not  prevent  the  voice  being  formed.  Injury 
of  the  laryngeal  nerves  supplying  the  muscles  which  move  the 
vocal  cords  puts  an  end  to  the  formation  of  vocal  sounds ;  and 
when  these  nerves  are  divided  on  both  sides,  the  loss  of  voice 
is  complete.  Moreover,  by  forcing  a  current  of  air  through 
the  larynx  in  the  dead  subject,  clear  vocal  sounds  are  pro- 
duced, though  the  epiglottis,  the  upper  ligaments  of  the 
larynx  or  false  vocal  cords,  the  ventricles  between  them,  and 
the  inferior  ligaments  or  true  vocal  cords,  and  the  upper  part 
of  the  arytenoid  cartilages,  be  all  removed  ;  provided  the  true 
vocal  cords  remain  entire,  with  their  points  of  attachment,  and 
be  kept  tense  and  so  approximated  that  the  fissure  of  the  glot- 
tis may  be  narrow. 

The  vocal  ligaments  or  cord,  therefore,  may  be  regarded  as 
the  proper  organs  of  the  mere  voice :  the  modifications  of  the 
voice  are  effected  by  other  parts  as  well  as  by  them.  Their 
structure  is  adapted  to  enable  them  to  vibrate  like  tense  mem- 
branes, for  they  are  essentially  composed  of  elastic  tissue ;  and 
they  are  so  attached  to  the  cartilaginous  parts  of  the  larynx 
that  their  position  and  tension  can  be  variously  altered  by  the 
contraction  of  the  muscles  which  act  on  these  parts. 

The  Larynx. 

The  larynx,  or  organ  of  voice,  consists  essentially  of  two 
elastic  lips  called  the  vocal  cords,  which  are  so  attached  to 
certain  cartilages,  and  so  under  the  control  of  certain  muscles, 
that  they  can  be  made  the  means  not  only  of  closing  the  larynx 
against  the  entrance  and  exit  of  air  to  or  from  the  lungs,  but 
also  can  be  stretched  or  relaxed,  shortened  or  lengthened,  in 
accordance  with  the  conditions  that  may  be  necessary  for  the 
air  in  passing  over  them,  to  set  them  vibrating  and  produce 
various  sounds.  Their  action  in  respiration  has  been  already 
referred  to  (p.  166),  in  connection  with  ordinary  tranquil  res- 
piration, and  also  (p.  182,  et  seq.)  with  other  respiratory  acts, 
in  which  the  opening  or  closing  of  the  glottis,  or,  in  other 
words,  the  close  apposition  or  separation  of  the  vocal  cords,  is 
an  essential  part  of  the  performance.  In  these  respiratory 
acts,  however,  any  sound  that  may  be  produced,  as  in  cough- 
ing, is,  so  to  speak,  an  accident,  and  not  performed  with  pur- 
pose. In  the  present  chapter  the  sound  produced  by  the  vibra- 
tion of  the  vocal  cords  is  the  only  part  of  their  function  with 
which  we  have  to  deal. 

It  will  be  well,  perhaps,  to  refer  to  a  few  points  in  the  auat- 


THE     LARYNX. 


477 


omy  of  the  larynx,  before  considering  its  physiology  in  con- 
nection with  voice  and  speech. 

The  principal  parts  entering  into  the  formation  of  the  larynx 
(Figs.  169  and  170)  are— (t)  the  thyroid  cartilage;  (c)  the 


FIG.  169. 


Outline  showing  the  general  form  of  the  larynx,  trachea,  and  bronchi  as  seen  from 
behind.  %. — h,  great  cornu  of  the  hyoid  bone ;  t,  superior,  and  t',  the  inferior  cornu 
of  the  thyroid  cartilage ;  e,  the  epiglottis ;  a,  points  to  the  back  of  both  the  arytenoid 
cartilages,  which  are  surmounted  by  the  cornicula  ;  c,  the  middle  ridge  on  the  back 
of  the  cricoid  cartilage  ;  tr,  the  posterior  membranous  part  of  the  trachea ;  b,  b', 
right  and  left  bronchi. 


478 


VOICE    AND    SPEECH. 


cricoid  cartilage ;  (a)  the  two  arytenoid  cartilages ;  and  the 
two  true  vocal  cords  (A,  cv,  Fig.  172).  The  epiglottis  (Fig. 
170,  e)  has  but  little  to  do  with  the  voice,  and  is  chiefly 
useful  in  falling  down  as  a  "  lid  "  over  the  upper  part  of  the 
larynx,  to  prevent  the  entrance  of  food  and  drink  in  deglutition. 
The  false  vocal  cords  (cvs,  Fig.  172),  and  the  ventricle  of  the 
larynx,  which  is  a  space  between  the  false  and  the  true  cord 
of  either  side,  need  be  here  only  referred  to. 

The  thyroid  cartilage  (Fig.  170,  1  to  4)  does  not  form  a 
complete  ring  around  the  larynx,  but  only  covers  the  front 
portion.  The  cricoid  cartilage  (Fig.  170,  5,  6),  on  the  other 
hand,  is  a  complete  ring ;  the  back  part  of  the  ring  being  much 
broader  than  the  front.  On  the  top  of  this  broad  portion  of 
the  cricoid  are  the  arytenoid  cartilages  (Fig.  169,  a)  the  con- 
nection between  the  cricoid  below  and  arytenoid  cartilages 
above  being  a  joint  with  sy  no  vial  membrane  and  ligaments, 
the  latter  permitting  tolerably  free  motion  between  them. 

But,  although  the  arytenoid  carti- 
FlG  170  lages  can  move  on  the  cricoid,  they 

of  course  accompany  the  latter  in 
all  their  movements,  just  as  the 
head  may  nod  or  turn  on  the  top 
of  the  spinal  column,  but  must  ac- 
company it  in  all  its  movements  as 
a  whole. 

The  thyroid  cartilage  is  also  con- 
nected with  the  cricoid,  not  only 
by  ligaments,  but  by  two  joints  with 
synovial  membrane  (if,  Figs.  168 
and  169)  ;  the  lower  cortma  of  the 
thyroid  clasping,  or  nipping,  as  it 
were,  the  cricoid  between  them,  but 
not  so  tightly  but  that  the  thyroid 
can  revolve,  within  a  certain  range, 
around  an  axis  passing  transversely 
through  the  two  joints  at  which  the 
cricoid  is  clasped.  The  vocal  cords 
are  attached  (behind)  to  the  front 
portion  of  the  base  of  the  arytenoid 
cartilages,  and  (in  front)  to  the  re- 
entering  angle  at  the  back  part  of 
the  thyroid;  it  is  evident,  therefore, 
that  all  movements  of  either  of 
these  cartilages  must  produce  an 
effect  on  them  of  some  kind  or  other. 
Inasmuch,  too,  as  the  arytenoid  car- 


Cartilages  of  the  larynx  seen 
from  before.  %.— 1  to  4,  thyroid 
cartilage ;  1,  vertical  ridge  or  po- 
mum  Adami ;  2,  right  ala ;  3, 
superior,  and  4,  inferior  cornu  of 
the  right  side  ;  5,  6,  cricoid  carti- 
lage; 5,  inside  of  the  posterior 
part;  6,  anterior  narrow  part  of 
the  ring  ;  7,  arytenoid  cartilages. 


THE     LARYNX. 


479 


FIG.  171. 


tilages  rest  on  the  top  of  the  back  portion  of  the  cricoid  car- 
tilage (a,  Fig.  169),  and  are  connected  with  it  by  capsular  and 
other  ligaments,  all  movements  of  the  cricoid  cartilage  must 
move  the  arytenoid  cartilages,  and  also  produce  an  effect  on 
the  vocal  cords. 

The  so-called  intrinsic  muscles  of  the  larynx,  or  those  which, 
in  their  action,  have  a  direct  action  on  the  vocal  cords,  are 
nine  in  number — four  pairs,  and  a  single  muscle;  namely,  two 
crico-thyroid  muscles,  two  thyro-arytenoid,  two  posterior  crico- 
arytenoid,  two  lateral  crico-arytenoid,  and  one  arytenoid  muscle. 
Their  actions  are  as  follows :  When  the  crico-thyroid  muscles 
(10,  Fig.  171)  contract,  they 
rotate  the  cricoid  on  the  thyroid 
cartilage  in  such  a  manner  that 
the  upper  and  back  part  of  the 
former,  and  of  necessity  the  aryt- 
enoid cartilages  on  the  top  of 
it,  are  tipped  backwards,  while 
the  thyroid  is  inclined  forward ; 
and  thus,  of  course,  the  vocal 
cords  being  attached  in  front  to 
one,  and  behind  to  the  other, 
are  "put  on  the  stretch." 

The  thyro-arytenoid  muscles 
(7,  Fig.  174),  on  the  other  hand, 
have  an  opposite  action — pull- 
ing the  thyroid  backwards,  and 
the  arytenoid  and  upper  and 
back  part  of  the  cricoid  carti- 
lages forwards,  and  thus  relaxing 
the  vocal  cords. 

The  crico-arytenoidei  postici 
muscles  (Fig.  173,  b)  dilate  the 
glottis,  and  separate  the  vocal 
cords,  the  one  from  the  other, 
by  an  action  on  the  arytenoid 
cartilage,  which  will  be  plain  on  Chea. 
reference  to  B'  and  c',  Fig.  172. 
By  their  contraction  they  tend  to  pull  together  the  outer  angles 
of  the  arytenoid  cartilages  in  such  a  fashion  as  to  rotate  the 
latter  at  their  joint  with  the  cricoid,  and  of  course  to  throw 
asunder  their  anterior  angles  to  which  the  vocal  cords  are  at- 
tached. 

These  posterior  crico-arytenoid  muscles  are  opposed  by  the 
crico-arytenoidei  laterales,  which,  pulling  in  the  opposite  direc- 
tion from  the  other  side  of  the  axis  of  rotation,  have  of  course 


Lateral  view  of  exterior  of  the 
larynx,  after  Mr.  Willis.  8,  thyroid 
cartilage ;  9,  cricoid  cartilage ;  10, 
crico-thyroid  muscle;  11,  crico-thy- 
roid ligament;  12,  first  rings  of  tra- 


480 


VOICE    AND    SPEECH. 


exactly  the  opposite  effect,  and  close  the  glottis  (Fig.  174,  4 
and  5). 

The  aperture  of  the  glottis  can  be  also  contracted  by  the 
arytenoid  muscle  («,  Fig.  173,  and  6,  Fig.  174),  which,  in  its 


FIG. 172. 


Three  laryngoscopic  views  of  the  superior  aperture  of  the  larynx  and  surrounding 

parts  and  different  states  of  the  glottis  during  life  (from  Czermak). 
A,  the  glottis  during  the  emission  of  a  high  note  in  singing  ;  B,  in  easy  and  quiet 
inhalation  of  air;  C,  in  the  state  of  widest  possible  dilatation,  as  in  inhaling  a  very 
deep  breath.  The  diagrams  A',  B',  and  C',  have  been  added  to  Czermak's  figures,  to 
show  in  horizontal  sections  of  the  glottis  the  position  of  the  vocal  ligaments  and  aryt- 
enoid cartilages  in  the  three  several  states  represented  in  the  other  figures.  In  all 
the  figures,  so  far  as  marked,  the  letters  indicate  the  parts  as  follows,  viz. :  I,  the  base 
of  the  tongue;  e,  the  upper  free  part  of  the  epiglottis;  e',  the  tubercle  or  cushion  of 
the  epiglottis ;  ph,  part  of  the  anterior  wall  of  the  pharynx  behind  the  larynx ;  in  the 
margin  of  the  aryteno-epiglottidean  fold,  w,  the  swelling  of  the  membrane  caused  by 
the  cartilages  of  Wrisberg ;  s,  that  of  the  cartilages  of  Santorini ;  a,  the  tip  or  summit 
of  the  arytenoid  cartilages;  c  v,  the  true  vocal  cords  or  lips  of  the  rima  glottidis ;  c  vs, 
the  superior  or  false  vocal  cords;  between  them  the  ventricle  of  the  larynx ;  in  C,  tr 
is  placed  on  the  anterior  wall  of  the  receding  trachea,  and  b  indicates  the  commence- 
ment of  the  two  bronchi  beyond  the  bifurcation  which  may  be  brought  into  view  in 
this  state  of  extreme  dilatation  (from  Quain's  Anatomy). 


PRODUCTION    OF    VOCAL    SOUNDS.  481 

contraction,  pulls  together  the  upper  parts  of  the  arytenoid 
cartilages  between  which  it  extends. 

The  placing  of  the  vocal  cords  in  a  position  parallel  one 
with  the  other,  is  effected  by  a  combined  action  of  the  various 
little  muscles  which  act  on  them — the  thyro-arytenoidei  having, 
without  much  reason,  the  credit  of  taking  the  largest  share  in 
the  production  of  this  effect.  Fig.  172  is  intended  to  show  the 
various  positions  of  the  vocal  cords  under  different  circum- 
stances. Thus,  in  ordinary  tranquil  breathing,  the  opening 
of  the  glottis  is  wide  and  triangular,  becoming  a  little  wider 
at  each  inspiration,  and  a  little  narrower  at  each  expiration 
(Fig.  172,  see  also  p.  166).  On  making  a  rapid  and  deep 
inspiration  the  opening  of  the  glottis  is  widely  dilated,  as  in 
c,  Fig.  172,  and  somewhat  lozenge-shaped.  At  the  moment 
of  the  emission  of  sound,  it  is  more  narrowed,  the  margins  of 
the  aryteuoid  cartilages  being  brought  into  contact,  and  the 
edges  of  the  vocal  cords  approximated  and  made  parallel,  at 
the  same  time  that  their  tension  is  much  increased.  The 
higher  the  note  produced,  the  tenser  do  the  cords  become 
(Fig.  172,  A);  and  the  range  of  a  voice  depends,  of  course,  in 
the  main,  on  the  extent  to  which  the  degree  of  tension  of  the 
vocal  cords  can  be  thus  altered.  In  the  production  of  a  high 
note,  the  vocal  cords  are  brought  well  within  sight,  so  as  to  be 
plainly  visible  with  the  help  of  the  laryngoscope.  In  the  ut- 
terance of  grave  tones,  on  the  other  hand,  the  epiglottis  is 
depressed  and  brought  over  them,  and  the  aryteuoid  cartilages 
look  as  if  they  were  trying  to  hide  themselves  under  it  (Fig. 
175). 

The  epiglottis,  by  being  somewhat  pressed  down  so  as  to  cover 
the  superior  cavity  of  the  larynx,  serves  to  render  the  notes 
deeper  in  tone,  and  at  the  same  time  somewhat  duller,  just  as 
covering  the  end  of  a  short  tube  placed  in  front  of  caoutchouc 
tongues  lowers  the  tone.  In  no  other  respect  does  the  epiglottis 
appear  to  have  any  effect  in  modifying  the  vocal  sounds. 

The  degree  of  approximation  of  the  vocal  cords  also  usually 
corresponds  with  the  height  of  the  note  produced  ;  but  probably 
not  always,  for  the  width  of  the  aperture  has  no  essential  in- 
fluence on  the  height  of  the  note,  as  long  as  the  vocal  cords 
have  the  same  tension ;  only  with  a  wide  aperture,  the  tone  is 
more  difficult  to  produce,  and  is  less  perfect,  the  rushing  of  the 
air  through  the  aperture  being  heard  at  the  same  time. 

No  true  vocal  sound  is  produced  at  the  posterior  part  of  the 
aperture  of  the  glottis,  that,  viz.,  which  is  formed  by  the  space 
between  the  arytenoid  cartilages,  for,  as  Miiller's  experi- 
ments showed,  if  the  arytenoid  cartilages  be  approximated  in 
such  a  manner  that  their  anterior  processes  tpucfy  each  other, 


482 


VOICE    AND    SPEECH. 


but  yet  leave  an  opening  behind  them  as  well  as  in  front,  no 
second  vocal  tone  is  produced  by  the  passage  of  the  air  through 
the  posterior  opening,  but  merely  a  rustling  or  bubbling  sound ; 


FIG.  173. 


FIG.  174. 


FIG. 175. 


FIG.  173. — View  of  the  larynx  and  part  of  the  trachea  from  behind,  with  the  muscles 
dissected  ;  h,  the  body  of  the  hyoid  bone;  e,  epiglottis;  t,  the  posterior  borders  of  the 
thyroid  cartilage;  c,  the  median  ridge  of  the  cricoid;  a,  upper  part  of  the  arytenoid; 
s,  placed  on  one  of  the  oblique  fasciculi  of  the  arytenoid  muscle ;  b,  left  posterior 
crico-arytenoid  muscle  ;  ends  of  the  incomplete  cartilaginous  rings  of  the  trachea;  /, 
fibrous  membrane  crossing  the  back  of  the  trachea;  n,  muscular  fibres  exposed  in  a 
part  ('from  Quain's  Anatomy). 

FIG.  174. — View  of  the  larynx  from  above.  1,  aperture  of  glottis;  2,  arytenoid  car- 
tilages ;  3,  vocal  cords ;  4,  posterior  crico-arytenoid  muscles ;  5,  lateral  crico-arytenoid 
muscle  of  right  side,  that  of  left  side  removed  ;  6,  arytenoid  muscle ;  7,  thyro-aryte- 
iioid  muscle  of  left  side,  that  of  right  side  removed ;  8,  thyroid  cartilage ;  9,  cricoid 
cartilage;  13,  posterior  crico-arytenoid  ligament.  With  the  exception  of  the  aryte- 
noid muscle,  this  diagram  is  a  copy  from  Mr.  Willis's  figure. 

FIG.  175. — View  of  the  upper  part  of  the  larynx  as  seen  by  means  of  the  laryngo- 
scope during  the  utterance  of  a  grave  note,  c,  epiglottis ;  s,  tubercles  of  the  cartilages 
of  Santorini;  a,  arytenoid  cartilages;  z,  base  of  the  tongue;  ph,  the  posterior  wall  of 
the  pharynx. 

and  the  height  or  pitch  of  the  note  produced  is  the  same  whe- 
ther the  posterior  part  of  the  glottis  be  open  or  not,  provided 
the  vocal  cords  maintain  the  same  degree  of  tension. 


COMPASS    OF    THE    VOICE.  483 


Application  of  the  Voice  in  Singing  and  Speaking. 

The  notes  of  the  voice  thus  produced  may  observe  three  dif- 
ferent kinds  of  sequence.  The  first  is  the  monotonous,  in  which 
the  notes  have  nearly  all  the  same  pitch  as  in  ordinary  speak- 
ing ;  the  variety  of  the  sounds  of  speech  being  due  to  articula- 
tion in  the  mouth.  In  speaking,  however,  occasional  syllables 
generally  receive  a  higher  intonation  for  the  sake  of  accent. 
The  second  mode  of  sequence  is  the  successive  transition  from 
high  to  low  notes,  and  vice  versa,  without  intervals;  such  as  is 
heard  in  the  sounds,  which  as  expressions  of  passion  accompany 
crying  in  men,  and  in  the  howling  and  whining  of  dogs.  The 
third  mode  of  sequence  of  the  vocal  sounds  is  the  musical,  in 
which  each  sound  has  a  determinate  number  of  vibrations,  and 
the  numbers  of  the  vibrations  in  the  successive  sounds  have 
the  same  relative  proportions  that  characterize  the  notes  of  the 
musical  scale. 

The  compass  of  the  voice  in  different  individuals  comprehends 
one,  two,  or  three  octaves.  In  singers — that  is,  in  persons  apt 
for  singing — it  extends  to  two  or  three  octaves.  But  the  male 
and  female  voices  commence  and  end  at  different  points  of  the 
musical  scale.  The  lowest  note  of  the  female  voice  is  about  an 
octave  higher  than  the  lowest  of  the  male  voice ;  the  highest  note 
of  the  female  voice  about  an  octave  higher  than  the  highest 
of  the  male.  The  compass  of  the  male  and  female  voices  taken 
together,  or  the  entire  scale  of  the  human  voice,  includes  about 
four  octaves.  The  principal  difference  between  the  male  and 
female  voice  is,  therefore,  in  their  pitch  ;  but  they  are  also  dis- 
tinguished by  their  tone — the  male  voice  is  not  so  soft. 

The  voice  presents  other  varieties  besides  that  of  male  and 
female ;  there  are  two  kinds  of  male  voice,  technically  called 
the  bass  and  tenor,  and  two  kinds  of  female  voice,  the  contralto 
and  soprano,  all  differing  from  each  other  in  tone.  The  bass 
voice  usually  reaches  lower  than  the  tenor,  and  its  strength  lies 
in  the  low  notes ;  while  the  tenor  voice  extends  higher  than  the 
bass.  The  contralto  voice  has  generally  lower  notes  than  the 
soprano,  and  is  strongest  in  the  lower  notes  of  the  female  voice; 
while  the  soprano  voice  reaches  higher  in  the  scale.  But  the 
difference  of  compass,  and  of  power  in  different  parts  of  the 
scale,  is  not  the  essential  distinction  between  the  different 
voices ;  for  bass  singers  can  sometimes  go  very  high,  and  the 
contralto  frequently  sings  the  high  notes  like  soprano  singers. 
The  essential  difference  between  the  bass  and  tenor  voices,  and 
between  the  contralto  and  soprano,  consists  in  their  tone  or 
"timbre,"  which  distinguishes  them  even  when  they  are  sing- 
ing the  same  note.  The  qualities  of  the  baritone  and  mezzo- 


484  VOICE     AND    SPEECH. 

soprano  voices  are  less  marked  ;  the  baritone  being  intermedi- 
ate between  the  bass  and  tenor,  the  mezzosoprano  between  the 
contralto  and  soprano.  They  have  also  a  middle  position  as 
to  pitch  in  the  scale  of  the  male  and  female  voices. 

The  different  pitch  of  the  male  and  the  female  voice  depends 
on  the  different  length  of  the  vocal  cords  in  the  two  sexes ; 
their  relative  length  in  men  and  women  being  as  three  to  two. 
The  difference  of  the  two  voices  in  tone  or  "  timbre,"  is  owing 
to  the  different  nature  and  form  of  the  resounding  walls,  which 
in  the  male  larynx  are  much  more  extensive,  and  form  a  more 
acute  angle  anteriorly.  The  different  qualities  of  the  tenor 
and  bass,  and  of  the  alto  and  soprano  voices,  probably  depend 
on  some  peculiarities  of  the  ligaments,  and  the  membranous 
and  cartilaginous  parietes  of  the  laryngeal  cavity,  which  are 
not  at  present  understood,  but  of  which  we  may  form  some 
idea,  by  recollecting  that  musical  instruments  made  of  different 
materials,  e.  g.,  metallic  and  gut  strings,  may  be  tuned  to  the 
same  note,  but  that  each  will  give  it  with  a  peculiar  tone  or 
"  timbre." 

The  larynx  of  boys  resembles  the  female  larynx  ;  their  vocal 
cords  before  puberty  have  not  two-thirds  the  length  which  they 
acquire  at  that  period  ;  and  the  angle  of  their  thyroid  cartilage 
is  as  little  prominent  as  in  the  female  larynx.  Boys'  voices 
are  alto  and  soprano,  resembling  in  pitch  those  of  women,  but 
louder,  and  differing  somewhat  from  them  in  tone.  But,  after 
the  larynx  has  undergone  the  change  produced  during  the 
period  of  development  at  puberty,  the  boy's  voice  becomes  bass 
or  tenor.  While  the  change  of  form  is  taking  place,  the  voice 
is  said  to  "  crack  ;"  it  becomes  imperfect,  frequently  hoarse  and 
crowing,  and  is  unfitted  for  singing  until  the  new  tones  are 
brought  under  command  by  practice.  In  eunuchs,  who  have 
been  deprived  of  the  testes  before  puberty,  the  voice  does  not 
undergo  this  change.  The  voice  of  most  old  people  is  deficient 
in  tone,  unsteady,  and  more  restricted  in  extent :  the  first  de- 
fect is  owing  to  the  ossification  of  the  cartilages  of  the  larynx 
and  the  altered  condition  of  the  vocal  cord  ;  the  want  of  steadi- 
ness arises  from  the  loss  of  nervous  power  and  command  over 
the  muscles ;  the  result  of  which  is  here,  as  in  other  parts,  a 
tremulous  motion.  These  two  causes  combined  render  the 
voices  of  old  people  void  of  tone,  unsteady,  bleating,  and  weak. 

In  any  class  of  persons  arranged,  as  in  an  orchestra,  accord- 
ing to  the  characters  of  voices,  each  would  possess,  with  the 
general  characteristics  of  a  bass,  or  tenor,  or  any  other  kind  of 
voice,  some  peculiar  character  by  which  his  voice  would  be 
recognized  from  all  the  rest.  The  conditions  that  determine 
these  distinctions  are,  however,  quite  unknown.  They  are 


VARIETIES    OF    VOCAL    TONES.  485 

probably  inherent  in  the  tissues  of  the  larynx,  and  are  as  in- 
discernible as  the  minute  differences  that  characterize  men's 
features ;  one  often  observes,  in  like  manner,  hereditary  and 
family  peculiarities  of  voice  as  well  marked  as  those  of  the 
limbs  or  face. 

Most  persons,  particularly  men,  have  the  power,  if  at  all 
capable  of  singing,  of  modulating  their  voices  through  a  double 
series  of  notes  of  different  character :  namely,  the  notes  of  the 
natural  voice,  or  chest-notes,  and  the  falsetto  notes.  The  natural 
voice,  which  alone  has  been  hitherto  considered,  is  fuller,  and 
excites  a  distinct  sensation  of  much  stronger  vibration  and 
resonance  than  the  falsetto  voice,  which  has  more  a  flute- 
like  character.  The  deeper  notes  of  the  male  voice  can  be 
produced  only  with  the  natural  voice,  the  highest  with  the 
falsetto  only;  the  notes  of  middle  pitch  can  be  produced  either 
with  the  natural  or  falsetto  voice ;  the  two  registers  of  the 
voice  are  therefore  not  limited  in  such  a  manner  as  that  one 
ends  when  the  other  begins,  but  they  run  in  part  side  by  side. 

The  natural,  or  chest  notes,  are  produced  by  the  ordinary 
vibrations  of  the  vocal  cords.  The  mode  of  production  of  the 
falsetto  notes  is  still  obscure.  By  Miiller  they  are  thought  to 
be  due  to  vibrations  of  only  the  inner  borders  of  the  vocal  cords. 
In  the  opinion  of  Petrequin  and  Diday,  they  do  not  result  from 
vibrations  of  the  vocal  cords  at  all,  but  from  vibrations  of  the 
air  passing  through  the  aperture  of  the  glottis,  which  they  be- 
lieve assumes,  at  such  times,  the  contour  of  the  embouchure  of  a 
flute.  Others  (considering  some  degree  of  similarity  which  ex- 
ists between  the  falsetto  notes,  and  the  peculiar  tones  called 
harmonic,  which  are  produced  when,  by  touching  or  stopping 
a  harp-string  at  a  particular  point,  only  a  portion  of  its  length 
is  allowed  to  vibrate)  have  supposed  that,  in  the  falsetto  notes, 
portions  of  the  vocal  ligaments  are  thus  isolated,  and  made  to 
vibrate  while  the  rest  are  held  still.  The  question  cannot  yet 
be  settled ;  but  any  one  in  the  habit  of  singing  may  assure 
himself,  both  by  the  difficulty  of  passing  smoothly  from  one 
set  of  notes  to  the  other,  and  by  the  necessity  of  exercising 
himself  in  both  registers,  lest  he  should  become  very  deficient 
in  one,  that  there  must  be  some  great  difference  in  the  modes 
in  which  their  respective  notes  are  produced. 

The  strength  of  the  voice  depends  partly  on  the  degree  to 
which  the  vocal  cords  can  be  made  to  vibrate ;  and  partly  on 
the  fitness  for  resonance  of  the  membranes  and  cartilages  of 
the  larynx,  of  the  parietes  of  the  thorax,  lungs,  and  cavities 
of  the  mouth,  nostrils,  and  communicating  sinuses.  It  is  di- 
minished by  anything  which  interferes  with  such  capability  of 
vibration.  The  intensity  or  loudness  of  a  given  note  with 

41 


486  VOICE    AND    SPEECH. 

maintenance  of  the  same  "  pitch,"  cannot  be  rendered  greater 
by  merely  increasing  the  force  of  the  current  of  air  through 
the  glottis;  for  increase  of  the  force  of  the  current  of  air 
cceteris  paribus,  raises  the  pitch  both  of  the  natural  and  the 
falsetto  notes.  Yet,  since  a  singer  possesses  the  power  of  in- 
creasing the  loudness  of  a  note  from  the  faintest  "  piano  "  to 
"  fortissimo  "  without  its  pitch  being  altered,  there  must  be 
some  means  of  compensating  the  tendency  of  the  vocal  cords 
to  emit  a  higher  note  when  the  force  of  the  current  of  air  is 
increased.  This  means  evidently  consists  in  modifying  the 
tension  of  the  vocal  cords.  When  a  note  is  rendered  louder 
and  more  intense,  the  vocal  cords  must  be  relaxed  by  remission 
of  the  muscular  action,  in  proportion  as  the  force  of  the  cur- 
rent of  the  breath  through  the  glottis  is  increased.  When  a 
note  is  rendered  fainter,  the  reverse  of  this  must  occur. 

The  arches  of  the  palate  and  the  uvula  become  contracted 
during  the  formation  of  the  higher  notes ;  but  their  contraction 
is  the  same  for  a  note  of  given  height,  whether  it  be  falsetto 
or  not ;  and  in  either  case  the  arches  of  the  palate  may  be 
touched  with  the  finger,  without  the  note  being  altered.  Their 
action,  therefore  in  the  production  of  the  higher  notes  seems  to 
be  merely  the  result  of  involuntary  associate  nervous  action, 
excited  by  the  voluntarily  increased  exertion  of  the  muscles  of 
the  larynx.  If  the  palatine  arches  contribute  at  all  to  the 
production  of  the  higher  notes  of  the  natural  voice  and  the 
falsetto,  it  can  only  be  by  their  increased  tension  strengthen- 
ing the  resonance. 

The  office  of  the  ventricles  of  the  larynx  is  evidently  to  afford 
a  free  space  for  the  vibrations  of  the  lips  of  the  glottis ;  they 
may  be  compared  with  the  cavity  at  the  commencement  of  the 
mouth-piece  of  trumpets,  which  allows  the  free  vibration  of 
the  lips. 

SPEECH. 

Besides  the  musical  tones  formed  in  the  larynx,  a  great 
number  of  other  sounds  can  be  produced  in  the  vocal  tubes, 
between  the  glottis  and  the  external  apertures  of  the  air-pas- 
sages, the  combination  of  which  sounds  into  different  groups 
to  designate  objects,  properties,  actions,  &c.,  constitutes  lan- 
guage. The  languages  do  not  employ  all  the  sounds  which 
can  be  produced  in  this  manner,  the  combination  of  some 
with  others  being  often  difficult.  Those  sounds  which  are 
easy  of  combination  enter,  for  the  most  part,  into  the  forma- 
tion of  the  greater  number  of  languages.  Each  language  con- 
tains a  certain  number  of  such  sounds,  but  in  no  one  are  all 
brought  together.  On  the  contrary,  different  languages  are 


VARIETIES    OF    VOCAL    TONES.  487 

characterized  by  the  prevalence  in  them  of  certain  classes  of 
these  sounds,  while  others  are  less  frequent  or  altogether  ab- 
sent. 

The  sounds  produced  in  speech,  or  articulate  sounds,  are  com- 
monly divided  into  vowels  and  consonants ;  the  distinction  be- 
tween which  is,  that  the  sounds  for  the  former  are  generated 
by  the  larynx,  while  those  for  the  latter  are  produced  by 
interruption  of  the  current  of  air  in  some  part  of  the  air-pas- 
sages above  the  larynx.  The  term  consonant  has  been  given 
to  these  because  several  of  them  are  not  properly  sounded, 
except  consonantly  with  a  vowel.  Thus,  if  it  be  attempted  to 
pronounce  aloud  the  consonants  b,  d,  and  g,  or  their  modifica- 
tions, p,  t,  k,  the  intonation  only  follows  them  in  their  combi- 
nation with  a  vowel. 

To  recognize  the  essential  properties  of  the  articulate  sounds, 
we  must,  according  to  Muller,  first  examine  them  as  they  are 
produced  in  whispering,  and  then  investigate  which  of  them 
can  also  be  uttered  in  a  modified  character  conjoined  with 
local  tone.  By  this  procedure  we  find  two  series  of  sounds : 
in  one  the  sounds  are  mute,  and  cannot  be  uttered  with  a 
vocal  tone ;  the  sounds  of  the  other  series  can  be  formed  inde- 
pendently of  voice,  but  are  also  capable  of  being  uttered  in 
conjunction  with  it. 

All  the  vowels  can  be  expressed  in  a  whisper  without  vocal 
tone,  that  is,  mutely.  These  mute  vowel-sounds  differ,  how- 
ever, in  some  measure,  as  to  their  mode  of  production,  from 
the  consonants.  All  the  mute  consonants  are  formed  in  the 
vocal-tube  above  the  glottis,  or  in  the  cavity  of  the  mouth  or 
nose,  by  the  mere  rushing  of  the  air  between  the  surfaces 
differently  modified  in  disposition.  But  the  sound  of  the 
vowels,  even  when  mute,  has  its  source  in  the  glottis  though 
its  vocal  cords  are  not  thrown  into  the  vibrations  necessary 
for  the  production  of  voice ;  and  the  sound  seems  to  be 
produced  by  the  passage  of  the  current  of  air  between  the 
relaxed  vocal  cords.  The  same  vowel-sound  can  be  produced 
in  the  larynx  when  the  mouth  is  closed,  the  nostrils  being 
open,  and  the  utterance  of  all  vocal  tone  avoided.  This 
sound,  when  the  mouth  is  open,  is  so  modified  by  varied  forms 
of  the  oral  cavity,  as  to  assume  the  characters  of  the  vowels 
a,  i,  o,  u,  in  all  their  modifications. 

The  cavity  of  the  mouth  assumes  the  same  form  for  the 
articulation  of  each  of  the  mute  vowels  as  for  the  correspond- 
ing vowel  when  vocalized  ;  the  only  difference  in  the  two  cases 
lies  in  the  kind  of  sound  emitted  by  the  larynx.  Krantzen- 
stein  and  Kempelen  have  pointed  out  that  the  conditions 
necessary  for  changing  one  and  the  same  sound  into  the  differ- 


488  VOICE    AND    SPEECH. 

ent  vowels,  are  differences  in  the  size  of  two  parts — the  oral 
canal  and  the  oral  opening ;  and  the  same  is  the  case  with 
regard  to  the  mute  vowels.  By  oral  canal,  Kempeleu  means 
here  the  space  between  the  tongue  and  palate :  for  the  pro- 
nunciation of  certain  vowels  both  the  opening  of  the  mouth 
and  the  space  just  mentioned  are  widened  ;  for  the  pronuncia- 
tion of  other  vowels  both  are  contracted ;  and  for  others  one 
is  wide,  the  other  contracted.  Admitting  five  degrees  of  size, 
both  of  the  opening  of  the  mouth  and  of  the  space  between 
the  tongue  and  palate,  Kempelen  thus  states  the  dimensions  of 
these  parts  for  the  following  vowel-sounds : 
/ 

Vowel.  Sound.  Size  of  oral        Size  of  oral 

opening.  canal. 


a    as  in 

a  " 
e  " 
o  " 
oo  " 


'far,". 
'  name," 
'  theme," 
'go,"  . 
'cool," 


5  3 

4  2 

3  1 

2  4 

1  5 


Another  important  distinction  in  articulate  sounds  is,  that 
the  utterance  of  some  is  only  of  momentary  duration,  taking 
place  during  a  sudden  change  in  the  conformation  of  the 
mouth,  and  being  incapable  of  prolongation  by  a  continued 
expiration.  To  this  class  belong  6,  p,  d,  and  the  hard  g.  In 
the  utterance  of  other  consonants  the  sounds  may  be  continu- 
ous; they  may  be  prolonged,  ad  libitum,  as  long  as  a  particular 
disposition  of  the  mouth  and  a  constant  expiration  are  main- 
tained. Among  these  consonants  are  h,  m,  n,  /,  s,  r,  I.  Cor- 
responding differences  in  respect  to  the  time  that  may  be 
occupied  in  their  utterance  exist  in  the  vowel-sounds,  and  prin- 
cipally constitute  the  differences  of  long  and  short  syllables. 
Thus,  the  a  as  in  "far"  and  "fate,"  the  o  as  in  "go"  and 
"  fort,"  may  be  indefinitely  prolonged ;  but  the  same  vowels 
(or  more  properly  different  vowels  expressed  by  the  same  let- 
ters), as  in  "  can"  and  "  fact,"  in  "  dog"  and  "  rotten,"  cannot 
be  prolonged. 

All  sounds  of  the  first  or  explosive  kind  are  insusceptible  of 
combination  with  vocal  tone  ("  intonation "),  and  are  abso- 
lutely mute ;  nearly  all  the  consonants  of  the  second  or  con- 
tinuous kind  may  be  attended  with  "  intonation." 

The  peculiarity  of  speaking,  to  which  the  term  ventriloquism 
is  applied,  appears  to  consist  merely  in  the  varied  modification 
of  the  sounds  produced  in  the  larynx,  in  imitation  of  the  modi- 
fications which  voice  ordinarily  suffers  from  distance,  &c.  From 
the  observations  of  Miiller  and  Colombat,  it  seems  that  the 
essential  mechanical  parts  of  the  process  of  ventriloquism  con- 
sist in  taking  a  full  inspiration,  then  keeping  the  muscles  of 


THE    SENSES.  489 

the  chest  and  neck  fixed,  and  speaking  with  the  mouth  almost 
closed,  and  the  lips  and  lower  jaw  as  motionless  as  possible, 
while  air  is  very  slowly  expired  through  a  very  narrow  glottis  ; 
care  being  taken  also,  that  none  of  the  expired  air  passes 
through  the  nose.  But,  as  observed  by  Mu'ller,  much  of  the 
ventriloquist's  skill  in  imitating  the  voices  coming  from  par- 
ticular directions,  consists  in  deceiving  other  senses  than  hear- 
ing. We  never  distinguish  very  readily  the  direction  in  which 
sounds  reach  our  ear ;  and,  when  our  attention  is  directed  to  a 
particular  point,  our  imagination  is  very  apt  to  refer  to  that 
point  whatever  sounds  we  may  hear. 

The  tongue,  which  is  usually  credited  with  the  power  of 
speech — language  and  speech  being  often  employed  as  synony- 
mous terms — plays  only  a  subordinate,  although  very  impor- 
tant part.  This  is  well  shown  by  cases  in  which  nearly  the 
whole  organ  has  been  removed  on  account  of  disease.  Patients 
who  recover  from  this  operation  talk  imperfectly,  and  their 
voice  is  considerably  modified ;  but  the  loss  of  speech  is  con- 
fined to  those  letters,  in  the  pronunciation  of  which  the  tongue 
is  concerned. 


CHAPTER  XIX. 

THE   SENSES. 

SENSATION  consists  in  the  mind  receiving,  through  the  me- 
dium of  the  nervous  system,  and,  usually  as  the  result  of  the 
action  of  an  external  cause,  a  knowledge  of  certain  qualities 
or  conditions,  not  of  external  bodies  but  of  the  nerves  of  sense 
themselves ;  and  these  qualities  of  the  nerves  of  sense  are  in 
all  different,  the  nerve  of  each  sense  having  its  own  peculiar 
quality. 

There  are  two  principal  kinds  of  sensation,  named  common 
and  special.  The  first  is  the  consequence  of  the  ordinary  sen- 
sibility or  feeling  possessed  by  most  parts  of  the  body,  and  is 
manifested  when  a  part  is  touched,  or  in  any  ordinary  manner 
is  stimulated.  According  to  the  stimulus,  the  mind  perceives 
a  sensation  of  heat,  or  cold,  of  pain,  of  the  contact  of  hard, 
soft,  smooth,  or  rough  objects,  &c.  From  this,  also,  in  morbid 
states,  the  mind  perceives  itching,  tingling,  burning,  aching, 
and  the  like  sensations.  In  its  greatest  perfection,  common 
sensibility  constitutes  touch  or  tact.  Touch  is,  indeed,  usually 
classed  with  the  special  senses,  and  will  be  considered  in  the 
same  group  with  them ;  yet  it  differs  from  them  in  being  a 
property  common  to  many  nerves,  e.  g.,  all  the  sensitive  spinal 


490  THE    SENSES. 

nerves,  the  pneumogastric,  glosso-pharyngeal,  and  fifth  cerebral 
nerves,  and  in  its  impressions  being  communicable  through 
many  organs. 

Including  the  sense  of  touch,  the  special  senses  are  five  in 
number, — the  senses  of  sight,  hearing,  smell,  taste,  and  touch. 
The  manifestation  of  each  of  the  first  three  depends  on  the 
existence  of  a  special  nerve ;  the  optic  for  the  sense  of  sight, 
the  auditory  for  that  of  hearing,  and  the  olfactory  for  that  of 
smell.  The  sense  of  taste  appears  to  be  a  property  common 
to  branches  of  the  fifth  and  of  the  glosso-pharyngeal  nerves. 

The  senses,  by  virtue  of  the  peculiar  properties  of  their  sev- 
eral nerves,  make  us  acquainted  with  the  states  of  our  own 
body ;  and  thus  indirectly  inform  us  of  such  qualities  and 
changes  of  external  matter  as  can  give  rise  to  changes  in  the 
condition  of  the  nerves.  That  which  through  the  medium 
of  our  senses  is  actually  perceived  by  the  mind  is,  indeed, 
merely  a  property  or  change  of  condition  of  our  nerves ;  but 
the  mind  is  accustomed  to  interpret  these  modifications  in  the 
state  of  the  nerves  produced  by  external  influences  as  proper- 
ties of  the  external  bodies  themselves.  This  mode  of  regard- 
ing sensations  is  so  habitual  in  the  case  of  the  senses  which 
are  more  rarely  affected  by  internal  causes,  that  it  is  only  on 
reflection  that  we  perceive  it  to  be  erroneous.  In  the  case  of 
the  sense  of  feeling,  on  the  contrary,  where  many  of  the  pecu- 
liar sensations  of  the  nerves  perceived  by  the  sensorium  are 
excited  as  frequently  by  internal  as  by  external  causes,  we 
more  readily  apprehend  the  truth.  For  it  is  easily  conceived 
that  the  feeling  of  pain  or  pleasure,  for  example,  is  due  to  a 
condition  of  the  nerves,  and  is  not  a  property  of  the  things 
which  excite  it.  What  is  true  of  these  is  true  of  all  other 
sensations ;  the  mind  perceives  conditions  of  the  optic,  olfac- 
tory, and  other  nerves  specifically  different  from  that  of  their 
state  of  rest ;  these  conditions  may  be  excited  by  the  contact 
of  external  objects,  but  they  may  also  be  the  consequence  of 
internal  changes :  in  the  former  case  the  mind,  having  knowl- 
edge of  the  object  through  either  instinct  or  instruction,  rec- 
ognizes it  by  the  appropriate  changes  which  it  produces  in  the 
state  of  the  nerves. 

The  special  susceptibility  of  the  different  nerves  of  sense  for 
certain  influences, — as  of  the  optic  nerve,  or  rather  its  centre, 
for  light ;  of  the  auditory  nerve,  or  centre,  for  vibrations  of 
the  air,  &c.,  and  so  on, — is  not  due  entirely  to  those  nerves 
having  each  a  specific  irritability  for  such  influences  exclu- 
sively. For  although,  in  the  ordinary  events  of  life,  the  optic 
nerve  is  excited  only  by  the  undulations  or  emanations  of  which 
light  may  consist,  the  auditory  only  by  vibrations  of  the  air, 


THE    SENSES.  491 

and  the  olfactory  only  by  odorous  particles — yet  each  of  these 
nerves  may  have  its  peculiar  properties  called  forth  by  other 
conditions.  In  fact,  in  whatever  way  and  to  whatever  degree 
a  nerve  of  special  sense  is  stimulated,  the  sensation  produced 
is  essentially  of  the  same  kind ;  irritation  of  the  optic  nerve 
invariably  producing  a  sensation  of  light,  of  the  auditory  nerve 
a  sensation  of  some  modification  of  sound.  The  phenomenon 
must,  therefore,  be  ascribed  to  a  peculiar  quality  belonging  to 
each  nerve  of  special  sense.  It  has  been  supposed,  indeed, 
that  irritation  of  a  nerve  of  special  sense,  when  excessive,  may 
produce  pain  ;  but  experiments  seem  to  have  proved  that  none 
of  these  nerves  possess  the  faculty  of  common  sensibility. 
Thus  Magendie  observed  that  when  the  olfactory  nerves  laid 
bare  in  a  dog  were  pricked,  no  signs  of  pain  were  manifested ; 
and  other  experiments  of  his  seemed  to  show  that  both  the 
retina  and  optic  nerve  are  insusceptible  of  pain. 

External  impressions  on  a  nerve  can  give  rise  to  no  kind  of 
sensation  which  cannot  also  be  produced  by  internal  causes, 
exciting  changes  in  the  condition  of  the  same  nerve.  In  the 
case  of  the  sense  of  touch,  this  is  at  once  evident.  The  sensa- 
tions of  the  nerves  of  touch  (or  common  sensibility),  excited 
by  causes  acting  from  without,  are  those  of  cold  and  heat, 
pain  and  pleasure,  and  innumerable  modifications  of  these, 
which  have  the  same  kind  of  sensation  as  their  element.  All 
these  sensations  are  constantly  being  produced  by  internal 
causes,  in  all  parts  of  our  body  endowed  with  sensitive  nerves. 
The  sensations  of  the  nerves  of  touch  are  therefore  states  or 
qualities  proper  to  themselves,  and  merely  rendered  manifest 
by  exciting  causes,  whether  external  or  internal.  The  sensa- 
tion of  smell,  also,  may  be  perceived  independently  of  the  ap- 
plication of  any  odorous  substance  from  without,  through  the 
influence  of  some  internal  condition  of  the  nerve  of  smell. 
The  sensations  of  the  sense  of  vision,  namely,  color,  light,  and 
darkness,  are  also  often  perceived  independently  of  all  external 
exciting  causes.  So,  also,  whenever  the  auditory  nerve  is  in  a 
state  of  excitement,  the  sensations  peculiar  to  it,  as  the  sounds 
of  ringing,  humming,  &c.,  are  perceived. 

The  same  cause,  whether  internal  or  external,  excites  in  the 
different  senses  different  sensations ;  in  each  sense  the  sensa- 
tions peculiar  to  it.  For  instance,  one  uniform  internal  cause, 
which  may  act  on  all  the  nerves  of  the  senses  in  the  same 
manner,  is  the  accumulation  of  blood  in  their  capillary  vessels, 
as  in  congestion  and  inflammation.  This  one  cause  excites  in 
the  retina,  while  the  eyes  are  closed,  the  sensations  of  light 
and  luminous  flashes  ;  in  the  auditory  nerve,  the  sensation  of 
humming  and  ringing  sounds ;  in  the  olfactory  nerve,  the 


492  THE    SENSES. 

sense  of  odors ;  and  in  the  nerves  of  feeling,  the  sensation  of 
pain.  In  the  same  way,  also,  a  narcotic  substance  introduced 
into  the  blood,  excites  in  the  nerves  of  each  sense  peculiar 
symptoms ;  in  the  optic  nerves,  the  appearance  of  luminous 
sparks  before  the  eyes;  in  the  auditory  nerves,  "tinnitus  au- 
rium ;"  and  in  the  common  sensitive  nerves,  the  sensation  of 
creeping  over  the  surface.  So,  also,  among  external  causes, 
the  stimulus  of  electricity,  or  the  mechanical  influence  of  a 
blow,  concussion,  or  pressure,  excites  in  the  eye  the  sensation 
of  light  and  colors ;  in  the  ear,  a  sense  of  a  loud  sound  or  of 
ringing ;  in  the  tongue,  a  saline  or  acid  taste ;  and  at  the  other 
parts  of  the  body,  a  perception  of  peculiar  jarring  or  of  me- 
chanical impression,  or  a  shock  like  it. 

Although,  in  the  cases  just  referred  to,  and  in  all  ordinary 
conditions,  sensations  are  derived  from  peculiar  conditions  of 
the  nerves  of  sense,  whether  excited  by  external  or  by  internal 
causes,  yet  the  mind  may  have  the  same  sensations  independ- 
ently of  changes  in  the  conditions  of  at  least  the  peripheral 
portions  of  the  several  nerves,  and  even  independently  of  any 
connection  with  the  external  organs  of  the  senses.  The  causes 
of  such  sensations  are  seated  in  the  parts  of  the  brain  in  which 
the  several  nerves  of  sense  terminate.  Thus  pressure  on  the 
brain  has  been  observed  to  cause  the  sensation  of  light:  lumi- 
nous spectra  may  be  excited  by  internal  causes  after  complete 
amaurosis  of  the  retina ;  and  Humboldt  states,  that,  in  a  man 
who  had  lost  one  eye,  he  produced  by  means  of  galvanism, 
luminous  appearances  on  the  blind  side.  Many  of  the  various 
morbid  sensations  attending  diseases  of  the  brain,  the  vision 
of  spectra,  and  the  like,  are  of  the  same  kind. 

Again,  although  the  immediate  objects  of  the  perception  of 
our  senses  are  merely  particular  states  induced  in  the  nerves, 
and  felt  as  sensations,  yet,  inasmuch  as  the  nerves  of  the  senses 
are  material  bodies,  and  therefore  participate  in  the  properties 
of  matter  generally,  occupying  space,  being  susceptible  of  vi- 
bratory motion,  and  capable  of  being  variously  changed  chem- 
ically, as  well  as  by  the  action  of  heat  and  electricity,  they 
make  known  to  the  mind,  by  virtue  of  the  different  changes 
thus  produced  in  them  by  external  causes,  not  merely  their 
own  condition,  but  also  some  of  the  different  properties  and 
changes  of  condition  of  external  bodies ;  as,  e.  g.,  progressive 
and  tremulous  motion,  chemical  change,  &c.  The  information 
concerning  external  nature  thus  obtained  by  the  senses,  varies 
in  each  sense,  having  a  relation  to  the  peculiar  qualities  or 
energies  of  the  nerve. 

The  sensation  of  motion  is,  like  motion  itself,  of  two  kinds — 
progressive  and  vibratory.  The  faculty  of  the  perception  of 


THE    SENSES.  493 

progressive  motion  is  possessed  chiefly  by  the  senses  of  vision, 
touch,  and  taste.  Thus  an  impression  is  perceived  travelling 
from  one  part  of  the  retina  to  another,  and  the  movement  of 
the  image  is  interpreted  by  the  mind  as  the  motion  of  the 
object.  The  same  is  the  case  in  the  sense  of  touch ;  so  also  the 
movement  of  a  sensation  of  taste  over  the  surface  of  the  organ 
of  taste,  can  be  recognized.  The  motion  of  tremors,  or  vibra- 
tions, is  perceived  by  several  senses,  but  especially  by  those  of 
hearing  and  touch.  For  the  sense  of  hearing,  vibrations  con- 
stitute the  ordinary  stimulus,  and  so  give  rise  to  the  perception 
of  sound.  By  the  sense  of  touch,  vibrations  are  perceived  as 
tremors,  ocasionally  attended  with  the  general  impression  of 
tickling;  for  instance,  when  a  vibrating  body,  such  as  a  tuning- 
fork,  is  approximated  to  a  very  sensible  part  of  the  surface, 
the  eye  can  communicate  to  the  mind  the  image  of  a  vibrating 
body,  and  can  distinguish  the  vibrations  when  they  are  very 
slow ;  it  may  be  also  that  the  vibrations  are  communicated  to 
the  optic  as  to  the  auditory  nerve  in  such  a  manner  that  it  re- 
peats them,  or  receives  their  impulses. 

We  are  made  acquainted  with  chemical  actions  principally 
by  taste,  smell,  and  touch,  and  by  each  of  these  senses  in  the 
mode  proper  to  it.  Volatile  bodies  disturbing  the  conditions 
of  the  nerves  by  a  chemical  action,  exert  the  greatest  influence 
upon  the  organ  of  smell ;  and  many  matters  act  on  that  sense 
which  produce  no  impression  upon  the  organs  of  taste  and 
touch ;  for  example,  many  odorous  substances,  as  the  vapor  of 
metals,  such  as  lead,  and  the  vapor  of  many  minerals.  Some 
volatile  substances,  however,  are  perceived  not  only  by  the 
sense  of  smell,  but  also  by  the  senses  of  touch  and  taste,  pro- 
vided they  are  of  a  nature  adapted  to  disturb  chemically  the 
condition  of  those  organs,  and  in  case  of  the  organ  of  taste,  to 
be  dissolved  by  the  fluids  covering  it.  Thus,  the  vapors  of 
horseradish  and  mustard,  and  acrid  suffocating  gases,  act 
upon  the  conjunctiva  and  the  mucous  membrane  of  the  lungs, 
exciting  through  the  common  sensitive  nerves,  merely  modi- 
fications of  common  feeling;  and  at  the  same  time  they  excite 
the  sensations  of  smell  and  of  taste. 

Sensations  are  referred  from  their  proper  seat  towards  the 
exterior ;  but  this  is  owing,  not  to  anything  in  the  nature  of 
the  nerves  themselves,  but  to  the  accompanying  idea  derived 
from  experience.  For  in  the  perception  of  sensations,  there  is 
a  combined  action  both  of  the  mind  and  of  the  nerves  of  sense; 
and  the  mind,  by  education  or  experience,  has  learned  to  refer 
the  impressions  it  receives  to  objects  external  to  the  body. 
Even  when  it  derives  impressions  from  internal  causes,  it  com- 
monly refers  them  to  external  objects.  The  light  perceived 

42 


494  THE    SENSES. 

in  congestion  of  the  retina  seems  external  to  the  body ;  the 
ringing  of  the  ears  in  disease  is  felt  as  if  the  sound  came  from 
some  distance ;  the  mind  referring  it  to  the  outer  world  from 
which  it  is  in  the  habit  of  receiving  the  like  impression. 

Moreover,  the  mind  not  only  perceives  the  sensations,  and 
interprets  them  according  to  ideas  previously  obtained,  but  it 
has  a  direct  influence  upon  them,  imparting  to  them  intensity 
by  its  faculty  of  attention.  Without  simultaneous  attention, 
all  sensations  are  only  obscurely,  if  at  all,  perceived.  If  the 
mind  be  torpid  in  indolence,  or  if  the  attention  be  withdrawn 
from  the  nerves  of  sense  in  intellectual  contemplation,  deep 
speculations,  or  an  intense  passion,  the  sensations  of  the  nerves 
make  no  impression  upon  the  mind  ;  they  are  not  perceived, — 
that  is  to  say,  they  are  not  communicated  to  the  conscious 
"  self,"  or  with  so  little  intensity,  that  the  mind  is  unable  to 
retain  the  impression,  or  only  recollects  it  some  time  after, 
when  it  is  freed  from  the  preponderating  influence  of  the  idea 
which  had  occupied  it. 

This  power  of  attention  to  the  sensations  derived  from  a 
single  organ,  may  also  be  exercised  in  a  single  portion  of  a 
sentient  organ,  and  thus  enable  one  to  discern  the  detail  of 
what  would  otherwise  be  a  single  sensation.  For  example,  by 
well-directed  attention,  one  can  distinguish  each  of  the  many 
tones  simultaneously  emitted  by  an  orchestra,  and  can  even 
follow  the  weaker  tones  of  one  instrument  apart  from  the  other 
sounds,  of  which  the  impressions  being  not  attended  to  are  less 
vividly  perceived.  So,  also  if  one  endeavors  to  direct  atten- 
tion to  the  whole  field  of  vision  at  the  same  time,  nothing  is 
seen  distinctly  ;  but  when  the  attention  is  directed  first  to  this, 
then  to  that  part,  and  analyzes  the  detail  of  the  sensation,  the 
part  to  which  the  mind  is  directed  is  perceived  with  more  dis- 
tinctness than  the  rest  of  the  same  sensation. 

THE   SENSE   OF   SMELL. 

The  sense  of  smell  ordinarily  requires,  for  its  excitement  to 
a  state  of  activity,  the  action  of  external  matters,  which  action 
produces  certain  changes  in  the  olfactory  nerve ;  and  this 
nerve  is  susceptible  of  an  infinite  variety  of  states  dependent 
on  the  nature  of  the  external  stimulus. 

The  first  condition  essential  to  the  sense  of  smell  is  the  exis- 
tence of  a  special  nerve,  the  changes  in  whose  condition  are 
perceived  as  sensations  of  odor ;  for  no  other  nerve  is  capable 
of  these  sensations,  even  though  acted  on  by  the  same  causes. 
The  same  substance  which  excites  the  sensation  of  smell  in  the 
olfactory  nerves  may  cause  another  peculiar  sensation  through 
the  nerves  of  taste,  and  may  produce  an  irritating  and  burn- 


THE     SENSE     OF     SMELL.  495 

ing  sensation  on  the  nerves  of  touch  ;  but  the  sensation  of  odor 
is  yet  separate  and  distinct  from  these,  though  it  may  be  sim- 
ultaneously perceived.  The  second  condition  of  smell  is  a  pe- 
culiar state  of  the  olfactory  nerve,  or  a  peculiar  change  pro- 
duced in  it  by  the  stimulus  or  odorous  substance. 

The  material  causes  of  odors  are,  usually,  in  the  case  of  ani- 
mals living  in  the  air,  either  solids  suspended  in  a  state  of  ex- 
tremely fine  division  in  the  atmosphere  ;  or  gaseous  exhalations 
often  of  so  subtile  a  nature  that  they  can  be  detected  by  no 
other  reagent  than  the  sense  of  smell  itself.  The  matters  of 
odor  must,  in  all  cases,  be  dissolved  in  the  mucus  of  the  mu- 
cous membrane  before  they  can  be  immediately  applied  to,  or 
affect  the  olfactory  nerves  ;  therefore  a  further  condition  neces- 
sary for  the  perception  of  odors  is,  that  the  mucous  membrane 
of  the  nasal  cavity  be  moist.  When  the  Schneiderian  mem- 
brane is  dry,  the  sense  of  smell  is  impaired  or  lost ;  in  the  first 
stage  of  catarrh,  when  the  secretion  of  mucus  within  the  nos- 
trils is  lessened,  the  faculty  of  perceiving  odor  is  either  lost,  or 
rendered  very  imperfect. 

In  animals  living  in  the  air,  it  is  also  requisite  that  the 
odorous  matter  should  be  transmitted  in  a  current  through 
the  nostrils.  This  is  effected  by  an  inspiratory  movement,  the 
mouth  being  closed ;  hence  we  have  voluntary  influence  over 
the  sense  of  smell ;  for  by  interrupting  respiration  we  prevent 
the  perception  of  odors,  and  by  repeated  quick  inspiration,  as- 
sisted, as  in  the  act  of  sniffing,  by  the  action  of  the  nostrils, 
we  render  the  impression  more  intense  (see  p.  184). 

The  human  organ  of  smell  is  essentially  formed  by  the  fila- 
ments of  the  olfactory  nerves,  distributed  in  minute  arrange- 
ment, in  the  mucous  membrane  covering  the  upper  third  of  the 
septum  of  the  nose,  the  superior  turbinated  or  spongy  bone, 
the  upper  part  of  the  middle  turbinated  bone,  and  the  upper 
wall  of  the  nasal  cavities  beneath  the  cribriform  plates  of  the 
ethmoid  bones  (Figs.  176  and  177). 

This  olfactory  region  is  covered  by  cells  of  cylindrical  epithe- 
lium not  provided  with  cilia ;  and  interspersed  with  these  are 
peculiar  fusiform  cells  with  fine  processes,  called  olfactory  cells. 
They  are  supposed  to  have  some  connection  with  the  terminal 
filaments  of  the  olfactory  nerve.  The  lower,  or  respiratory 
part,  as  it  is  called,  of  the  nasal  fossae  is  lined  by  cyliindrical 
ciliated  epithelium,  except  in  the  region  of  the  nostrils,  where 
it  is  squamous. 

In  all  the  distribution,  the  branches  of  the  olfactory  nerves 
retain  much  of  the  same  soft  and  grayish  texture  which  dis- 
tinguishes their  trunks  (as  the  olfactory  lobes  of  the  brain  are 
called)  within  the  cranium.  Their  individual  filaments,  also, 


496  THE    SEXSE    OF    SMELL. 

are  peculiar,  more  resembling  those  of  the  sympathetic  nerve 
than  the  filaments  of  the  other  cerebral  nerves  do,  containing 


Fw.  176. 


Nerves  of  the  septum  nasi,  seen  from  the  right  side  (from  Sappey  after  Hirschfeld 
and  Leveille).  %. — I,  the  olfactory  bulb;  1,  the  olfactory  nerves  passing  through 
the  foramina  of  the  cribriform  plate,  and  descending  to  be  distributed  on  the  septum  ; 
2,  the  internal  or  septal  twig  of  the  nasal  branch  of  the  ophthalmic  nerve ;  3,  naso- 
palatine  nerves. 

no  outer  white  substance,  and  being  finely  granular  and  nu- 
cleated. The  branches  are  distributed  principally  in  close 
plexuses ;  but  the  mode  of  termination  of  the  filaments  is  not 
yet  satisfactorily  determined. 

The  sense  of  smell  is  derived  exclusively  through  those  parts 
of  the  nasal  cavities  in  which  the  olfactory  nerves  are  dis- 
tributed ;  the  accessory  cavities  or  sinuses  communicating  with 
the  nostrils  seem  to  have  no  relation  to  it.  Air  impregnated 
with  the  vapor  of  camphor  was  injected  by  Deschamps  into 
the  frontal  sinus  through  a  fistulous  opening,  and  Richerand 
injected  odorous  substances  into  the  antrum  of  Highmore; 
but  in  neither  case  was  any  odor  perceived  by  the  patient. 
The  purposes  of  these  sinuses  appear  to  be,  that  the  bones, 
necessarily  large  for  the  action  of  the  muscles  and  other 
parts  connected  with  them,  may  be  as  light  as  possible,  and 
that  there  may  be  more  room  for  the  resonance  of  the  air  in 
vocalizing.  The  former  purpose,  which  is  in  other  bones  ob- 
tained by  filling  their  cavities  with  fat,  is  here  attained,  as  it 
is  in  many  bones  of  birds,  by  their  being  filled  with  air. 

All  parts  of  the  nasal  cavities,  whether  or  not  they  can  be 
the  seats  of  the  sense  of  smell,  are  endowed  with  common  sen- 
sibility by  the  nasal  branches  of  the  first  and  second  divisions 


THE    SENSE    OF    SMELL.  497 

of  the  fifth  nerve.  Hence  the  sensations  of  cold,  heat,  itching, 
tickling,  and  pain ;  and  the  sensation  of  tension  or  pressure  in 
the  nostrils.  That  these  nerves  cannot  perform  the  function 
of  the  olfactory  nerves  is  proved  by  cases  in  which  the  sense 

FIG.  177. 


Left  olfactory  nerve,  with  its  distribution  on  the  septum  narium  (from  Wilson). 

1,  Frontal  sinus ;  2,  nasal  bone  ;  3,  crista  galli  of  ethmoid  bone ;  4,  sphenoidal  sinus 
of  left  side  ;  5,  sella  turcica;  6,  basilar  process  of  sphenoid  and  occipital  bone ;  7,  pos- 
terior opening  of  the  right  naris  ;  8,  Opening  of  the  Eustachian  tube  in  the  upper 
part  of  the  pharynx ;  9,  soft  palate  divided  through  its  middle ;  10,  cut  surface  of  the 
hard  palate  ;  a,  olfactory  nerve;  b,  its  three  roots  of  origin  ;  c,  the  olfactory  bulb;  d, 
nasal  nerve  (ophthalmic  division  of  5th) ;  e,  naso-palatine  nerve  (from  the  spheno- 
palatine  ganglion);  /,  the  anterior  palatine  foramen  ;  g,  branches  of  the  naso-pala- 
tine nerve  to  the  palate  ;  A,  anterior  and  posterior  palatine  nerves;  i,  septum  narium. 

of  smell  is  lost,  while  the  mucous  membrane  of  the  nose  re- 
mains susceptible  of  the  various  modifications  of  common  sen- 
sation or  touch.  But  it  is  often  difficult  to  distinguish  the 
sensation  of  smell  from  that  of  mere  feeling,  and  to  ascertain 
what  belongs  to  each  separately.  This  is  the  case  particularly 
with  the  sensations  excited  in  the  nose  by  acrid  vapors,  as  of 
ammonia,  horseradish,  mustard,  &c.,  which  resemble  much 
the  sensations  of  the  nerves  of  touch  ;  and  the  difficulty  is  the 
greater,  when  it  is  remembered  that  these  acrid  vapors  have 
nearly  the  same  action  upon  the  mucous  membrane  of  the  eye- 
lids. It  was  because  the  common  sensibility  of  the  nose  to 
these  irritating  substances  remained  after  the  destruction  of 
the  olfactory  nerves,  that  Magendie  was  led  to  believe  the 
fifth  nerve  might  exercise  the  special  sense. 

Animals  do  not  all  equally  perceive  the  same  odors;  the 


498  THE    SENSE    OF    SMELL. 

odors  most  plainly  perceived  by  an  herbivorous  animal  and 
by  a  carnivorous  animal  are  different.  The  carnivora  have 
the  power  of  detecting  most  accurately  by  the  smell  the  special 
peculiarities  of  animal  matters,  and  of  tracking  other  animals 
by  the  scent ;  but  have  apparently  very  little  sensibility  to  the 
odors  of  plants  and  flowers.  Herbivorous  animals  are  pecu- 
liarly sensitive  to  the  latter,  and  have  a  narrower  sensibility 
to  animal  odors,  especially  to  such  as  proceed  from  other  in- 
dividuals than  their  own  species.  Man  is  far  inferior  to  many 
animals  of  both  classes  in  respect  of  the  acuteness  of  smell ; 
but  his  sphere  of  susceptibility  to  various  odors  is  more  uni- 
form and  extended.  The  cause  of  this  difference  lies  probably 
in  the  endowments  of  the  cerebral  parts  of  the  olfactory  ap- 
paratus. 

Opposed  to  the  sensation  of  an  agreeable  odor,  is  that  of  a 
disagreeable  or  disgusting  odor,  which  corresponds  to  the  sen- 
sations of  pain,  dazzling  and  disharmony  of  colors,  and  disso- 
nance in  the  other  senses.  The  cause  of  this  difference  in  the 
effect  of  different  odors  is  unknown  ;  but  this  much  is  certain, 
that  odors  are  pleasant  or  offensive  in  a  relative  sense  only, 
for  many  animals  pass  their  existence  in  the  midst  of  odors 
which  to  us  are  highly  disagreeable.  A  great  difference  in 
this  respect  is,  indeed,  observed  amongst  men :  many  odors, 
generally  thought  agreeable,  are  to  some  persons  intolerable ; 
and  different  persons  describe  differently  the  sensations  that 
they  severally  derive  from  the  same  odorous  substances.  There 
seems  also  to  be  in  some  persons  an  insensibility  to  certain 
odors,  comparable  with  that  of  the  eye  to  certain  colors ;  and 
among  different  persons,  as  great  a  difference  in  the  acuteuess 
of  the  sense  of  smell  as  among  others  in  the  acuteness  of  sight. 
We  have  no  exact  proof  that  a  relation  of  harmony  and  dis- 
harmony exists  between  odors  as  between  colors  and  sounds ; 
though  it  is  probable  that  such  is  the  case,  since  it  certainly  is 
so  with  regard  to  the  sense  of  taste ;  and  since  such  a  relation 
would  account  in  some  measure  for  the- different  degrees  of  per- 
ceptive power  in  different  persons ;  for  as  some  have  no  ear  for 
music  (as  it  is  said)  so  others  have  no  clear  appreciation  of  the 
relation  of  odors,  and  therefore  little  pleasure  in  them. 

The  sensations  of  the  olfactory  nerves,  independent  of  the 
external  application  of  odorous  substances,  have  hitherto  been 
little  studied.  It  has  been  found  that  solutions  of  inodorous 
substances,  such  as  salts,  excite  no  sensation  of  odor  when  in- 
jected into  the  nostrils.  The  friction  of  the  electric  machine 
is,  however,  known  to  produce  a  smell  like  that  of  phosphorus. 
Hitter,  too,  has  observed,  that  when  galvanism  is  applied  to 
the  organ  of  smell,  besides  the  impulse  to  sneeze,  and  the  tick- 


THE    SENSE    OF    SIGHT. 


499 


ling  sensation  excited  in  the  filaments  of  the  fifth  nerve,  a 
smell  like  that  of  ammonia  was  excited  by  the  negative  pole, 
and  an  acid  odor  by  the  positive  pole ;  whichever  of  these  sen- 
sations was  produced,  it  remained  constant  as  long  as  the  circle 
was  closed,  and  changed  to  the  other  at  the  moment  of  the 
circle  being  opened.  Frequently  a  person  smells  something 
which  is  not  present,  and  which  other  persons  cannot  smell ; 
this  is  very  frequent  with  nervous  people,  but  it  occasionally 
happens  to  every  one.  In  a  man  who  was  constantly  conscious 
of  a  bad  odor,  the  arachnoid  was  found  after  death,  by  MM. 
Cullerier  and  Maignault,  to  be  beset  with  deposits  of  bone ; 
and  in  the  middle  of  the  cerebral  hemispheres  were  scrofulous 
cysts  in  a  state  of  suppuration.  Dubois  was  acquainted  with 
a  man  who,  ever  after  a  fall  from  his  horse,  which  occurred 
several  years  before  his  death,  believed  that  he  smelt  a  bad 
odor. 

THE    SENSE    OF    SIGHT. 

The  eyeball  or  the  organ  of  vision  (Fig.  178)  consists  of  a 
variety  of  structures  which  may  be  thus  enumerated : 

FIG.  178. 


Ciliary  muscle. 

Ciliary  process. 

Canal  of  Petit. 

Cornea. 

Anterior  chamber. 

Lens. 

Iris. 

Ciliary  process. 
Ciliarv  muscle. 


The  sclerotic,  or  outermost  coat,  envelops  about  five-sixths 
of  the  eyeball :  continuous  with  it,  in  front,  and  occupying  the 
remaining  sixth,  is  the  cornea .  The  cornea  and  front  portion 


500 


THE    SENSE    OF    SIGHT. 


FIG.  179. 


of  the  sclerotic  are  covered  by  mucous  membrane, — the  con- 
junctiva; that  which  covers  the  front  of  the  cornea  being  little 

more  than  squamous  epithelium. 
Immediately  within  the  sclerotic 
is  the  choroid  coat,  and  within 
the  choroid  is  the  retina.  The 
interior  of  the  eyeball  is  well- 
nigh  filled  by  the  aqueous  and 
vitreous  humors  and  the  crystal- 
line lens;  but  also,  there  is  sus- 
pended in  the  interior  a  contrac- 
tile and  perforated  curtain, — 
the  iris,  for  regulating  the  ad- 
mission of  light,  and  behind  the 
junction  of  the  sclerotic  and  cor- 
nea is  the  ciliary  muscles,  the 
function  of  which  is  to  adapt  the 
eye  for  seeing  objects  at  various 
distances. 

These  structures  may  be  now 
examined  rather  more  in  detail. 

The  sclerotic  coat  is  composed 
of  connective  tissue,  arranged 
in  variously  disposed  and  inter- 
communicating .layers.  It  is 
strong,  tough,  and  opaque,  and 
not  very  elastic. 

The  cornea  (Fig.  179)  is,  like 
the  sclerotic,  with  which  it  is 
continuous,  chiefly  of  a  fibrous 
structure,  but  the  fibres  are  so 
modified  and  arranged  as  to 
form  a  transparent  membrane 
for  the  passage  of  light.  Both 
in  front  of  and  behind  the  fib- 
__  rous  tissue  of  the  cornea  is  a 

structure  of  the  cornea  (after  BOW-  structureless  elastic  membrane 

man).    A  80;  B  and  O  soo.    A,  small    with  epithelium. 

pwrtionofaTertifal8ecttoIlofi^®0''  The  choroid,  which  is  the 
^arin  .  f  a  '  a>  conjunc  "  next  tunic  of  the  eye  within  the 
d/fibrouViaminrwUh'rucir^bod'ies  sclerotic  and  immediately  out- 
interspersed  between  them ;  d,  posterior  side  the  retina,  consists  of  a  thin 

elastic    lamina    or    membrane    of   De-  an(J  highly  vascular  membrane, 

mours;  e,  internal  epithelium  of  d.  B,  of  which  the  iuternal  surface  is 
epithelium  of  the  membrane  of  De-  -,  ,  i  f  11  i 

mours,  as  seen  looking  towards  its  sur-  C?™red    by    a    layer    of    black 

face.    O,  the  same  seen  in  section.  pigment-Cells.          I  he    principal 


THE     RETINA.  501 

use  of  the  choroid  is  to  absorb,  by  means  of  its  pigment,  those 
rays  of  light  which  pass  through  the  transparent  retina,  and 
thus  to  prevent  their  being  thrown  again  upon  the  retina,  so 
as  to  interfere  with  the  distinctness  of  the  images  there  formed. 
Hence  animals  in  which  the  choroid  is  destitute  of  pigment, 
and  human  albinos,  are  dazzled  by  daylight,  and  see  best  in 
the  twilight.  The  choroid  coat  ends  in  front  in  what  are  called 
the  ciliary  processes  (Fig.  180*). 

FIG.  180. 


Ciliary  processes  as  seen  from  behind.  £•— 1,  posterior  surface  of  the  iris  with  the 
sphincter  muscle  of  the  pupil ;  2,  anterior  part  of  the  choroid  coat ;  3,  one  of  the 
ciliary  processes,  of  which  about  seventy  are  represented. 

The  retina  (Fig.  181)  is  a  delicate  membrane,  concave,  with 
the  concavity  directed  forwards  and  ending  in  front,  near  the 
outer  part  of  the  ciliary  processes  in  a  finely  notched  edge — 
the  ora  serrata.  Semi-transparent  when  fresh,  it  soon  becomes 
clouded  and  opaque,  with  a  pinkish  tint  from  the  blood  in 
its  minute  vessels.  It  results  from  the  sudden  spreading  out 
or  expansion  of  the  optic  nerve,  of  whose  terminal  fibres,  ap- 
parently deprived  of  their  external  white  substance,  together 
with  nerve-cells,  it  is  essentially  composed. 

Exactly  in  the  centre  of  the  retina,  and  at  a  point  thus  cor- 
responding to  the  axis  of  the  eye  in  which  the  sense  of  vision 
is  most  perfect,  is  a  round  yellowish  elevated  spot,  about  ^4  of 
an  inch  in  diameter,  having  a  minute  aperture  at  its  summit, 
and  called,  after  its  discoverer,  the  yellow  spot  of  Scemmering. 
It  is  not  covered  by  the  fibrous  part  of  the  retina,  but  a  layer 
of  closely  set  cells  passes  over  it,  and  in  its  centre  is  a  minute 
depression  called  fovea  ceniralis.  About  y1^  of  an  inch  to  the 
inner  side  of  the  yellow  spot,  and  consequently  of  the  axis  of 
the  eye,  is  the  point  at  which  the  optic  nerve  spreads  out  its 


502  THE    SENSE    OF    SIGHT. 

fibres  to  form  the  retina.     This  is  the  only  point  of  the  surface 
of  the  retina  from  which  the  power  of  vision  is  absent. 


FIG.  181. 


C7i 


The  posterior  half  of  the  retina  of  the  left  eye  viewed  from  before  (after  Henle); 
*,  the  cut  edge  of  the  sclerotic  coat ;  ck,  the  choroid ;  r,  the  retina ;  in  the  interior  at 
the  middle,  the  macula  lutea  with  the  depression  of  the  fovea  centralis  is  represented 
by  a  slight  oval  shade ;  towards  the  left  side  the  light  spot  indicates  the  colliculus  or 
eminence  at  the  entrance  of  the  optic  nerve,  from  the.  centre  of  which  the  arteria 
centralis  is  seen  spreading  its  branches  into  the  retina,  leaving  the  part  occupied  by 
the  macula  comparatively  free. 

On  making  a  vertical  section  of  the  retina,  it  is  seen,  under 
the  microscope,  to  be  composed  of  several  layers,  which  differ 
from  each  other  in  structure  and  arrangement,  while  besides 
these  there  are  fibres,  the  so-called  fibres  of  Muller,  which  ex- 
tend through  the  different  layers,  and  perforate  them,  so  to 
speak.  Fig.  182  represents  a  vertical  section  of  a  small  piece 
of  the  retina.  On  examination  it  will  be  seen  that  there  are 
three  principal  layers,  bounded  on  the  inner  aspect  by  a  mem- 
brana  limitams,  and  on  the  outer  by  the  choroid  coat.  1.  The 
outermost  is  the  membrane  of  Jacob,  or  the  columnar  layer. 
2.  In  the  middle  is  the  granular  layer.  3.  The  innermost  is 
the  nervous  layer.  Each  of  these  layers,  again,  is  composed  of 
different  strata,  after  the  fashion  shown  in  the  figure. 

The  columnar  layer  (Jacob's  membrane)  is  composed  of  cyl- 
indrical or  staff-shaped  transparent  and  highly  refractive 
bodies,  arranged  perpendicularly  to  the  surface  of  the  retina, 
with  their  outer  extremities  imbedded,  to  a  greater  or  less 
depth,  in  a  layer  of  black  pigment  of  the  choroid  coat.  Re- 


THE     RETINA. 


503 


cent  researches  seem  to  have  determined  that  this  membrane, 
instead  of  being,  as  was  formerly  considered,  an  independent 
covering,  is  intimately  associated,  both  in  structure  and  func- 


FIG. 182. 


FIG. 182a. 


FIG.  182.— Vertical  section  of  retina  of  human  eye.  1,  bacillar  layer ;  2,  outer  layer 
granular;  3,  intermediate  fibrous  layer;  4,  inner  granular  layer;  5,  finely  granular 
gray  layer;  6,  layer  of  nerve-cells ;  7,  layer  of  fibre  of  optic  nerve;  8,  limitary  mem- 
brane. 

FIG.  18'2a. — Elements  of  human  retina.  1,  large  fibre  of  optic  nerve;  2,  very  fine 
fibre  of  the  same;  3,  rod  with  a  granule,/,  attached;  4,  a  similar  rod  with  a  fine  fibrous 
prolongation,  connecting  it  with  the  granule ;  5,  portions  of  rods  altered  by  the  action 
of  water;  6,  7,  two  cones,  b  b,  with  their  nuclei,  c  c,  their  bacillar  portions,  d  d,  and 
their  fine  fibrous  prolongations,  ee;  8,  radiating  fibre,  ee,  with  granule  of  outer  layer, 
y,  and  subdividing  in  the  bacillar  layer,  as  well  as  in  the  optic  layer,  h;  9,  connec- 
tion of  rods,  a,  with  granules  of  inner  layer,/,  granule  of  outer  layer,  g,  and  expan- 
sion of  the  fibre  proceeding  from  the  latter  in  the  optic  layer  at  h;  10,  similar  con- 
nection of  cone,  b,  c,  with  granule,  g,  and  with  nerve-cell,  I,  which  has  another 
librous  prolongation,  ni. 


tion,  with  the  sensitive  part  of  the  retina;  for  the  conical  and 
staff-shaped  bodies,  of  which  it  is  composed,  appear  to  be  con- 


504  THE    SENSE    OF    SIGHT. 

nected,  by  means  of  delicate  fibres  issuing  from  them,  with  the 
nerve-vesicles  of  the  retina,  and  even  to  become  continuous 
with  the  radiating  processes  which  some  of  these  vesicles  pre- 
sent. Concerning  the  use  of  these  bodies,  the  discovery  of 
their  connection  with  the  sensitive  part  of  the  retina  supports 
the  opinion  entertained  by  Kolliker  and  H.  Miiller,  that  their 
special  office  is  to  receive  and  transmit  impressions  of  light. 

The  structures  of  which  the  granular  layer  is  composed  are 
indicated  in  the  figure. 

The  nervous  layer  is  composed  of  nerve-corpuscles  and  nerve- 
fibres.  The  nerve-corpuscles  are  the  outermost,  and  are  most 
numerous  over  the  yellow  spot,  and  absent  altogether  from  the 
point  of  entrance  of  the  optic  nerve.  They  are  imbedded  in 
fine  molecular  matter,  which  also  forms  a  layer  outside  them. 
The  nerve-fibres  radiate  as  a  fine  membranous  network  from 
the  point  of  entrance  of  the  optic  nerve,  of  whose  fibres  they 
are  the  continuation.  They  end  probably  in  the  nerve-corpus- 
cles. The  fibres  are  absent  from  the  yellow  spot. 

Two  of  the  fibres  of  Mutter  are,  for  the  sake  of  illustration, 
arranged  in  the  figure  separately  on  each  side  of  the  layer 
which  they  perforate.  About  the  connection  of  the  fibres  of 
Miiller  there  is  some  uncertainty.  They  are  supposed  to  be 
connected  by  their  outer  ends  with  the  rods  and  cones;  and 
by  their  inner,  which  are  thought  to  be  modifications  of  con- 
nective tissue,  they  rest  on  the  membrana  limitans.  Between 
these  points  they  are  supposed  to  have  connections  also  with 
some  of  the  other  structures  through  which  they  pass,  espe- 
cially with  the  inner  layer  of  nuclei. 

The  retinal  bloodvessels  ramify  chiefly  in  the  nervous 
layer. 

The  structures  which  have  been  just  described  are  modified 
in  their  distribution  over  the  yellow  spot  in  the  following  man- 
ner: Of  the  columnar  layer,  or  membrani  Jacobi,  the  cones 
greatly  predominate;  of  the  nervous  layers  the  cells  are  nu- 
merous, while  the  nerve-fibres  are  absent.  There  are  capilla- 
ries here,  but  none  of  the  larger  branches  of  the  retinal  ar- 
teries. Opposite  the  fovea  centralis,  there  are,  moreover,  neither 
the  granular,  nor  the  fine  molecular  layer,  nor  the  fibres  of 
Miiller. 

By  means  of  the  retina  and  the  other  parts  just  described, 
a  provision  is  afforded  for  enabling  the  terminal  fibres  of  the 
optic  nerve  to  receive  the  impression  of  rays  of  light,  and  to 
communicate  them  to  the  brain,  in  which  they  excite  the  sen- 
sation of  vision.  But  that  light  should  produce  in  the  retina 
images  of  the  objects  from  which  it  comes,  it  is  necessary  that, 


REFRACTION     BY    THE    CORNEA.  505 

when  emitted  or  reflected  from  determinate  parts  of  the  exter- 
nal objects,  it  should  stimulate  only  corresponding  parts  of  the 
retina.  For  as  light  radiates  from  a  luminous  body  in  all  di- 
rections, when  the  media  offer  no  impediment  to  its  transmis- 
sion, a  luminous  point  will  necessarily  illuminate  all  parts  of 
a  surface,  such  as  the  retina  opposed  to  it,  and  not  merely  one 
single  point.  A  retina,  therefore,  without  any  optical  appa- 
ratus placed  in  front  of  it  to  separate  the  light  of  different 
objects,  would  see  nothing  distinctly,  but  would  merely  per- 
ceive the  general  impression  of  daylight,  and  distinguish  it 
from  the  night.  Accordingly,  we  find  that  in  man,  and  all 
vertebrate  animals,  certain  transparent  refracting  media  are 
placed  in  front  of  the  retina  for  the  purpose  of  collecting  to- 
gether into  one  point,  the  different  divergent  rays  emitted  by 
each  point  of  the  external  body,  and  of  giving  them  such  di- 
rections that  they  shall  fall  on  corresponding  points  of  the 
retina,  and  thus  produce  an  exact  image  of  the  object  from 
which  they  proceed.  These  refracting  media  are,  in  the  order 
of  succession  from  without  inwards,  the  cornea,  the  aqueous 
humor,  the  crystalline  lens,  and  the  vitreous  humor  (Fig.  178). 

The  cornea,  the  structure  of  which  has  been  already  referred 
to  (p.  500),  is  in  a  twofold  manner  capable  of  refracting  and 
causing  convergence  of  the  rays  of  light  that  fall  upon  and 
traverse  it.  It  thus  affects  them  first,  by  its  density  ;  for  it  is 
a  law  in  optics  that  when  rays  of  light  pass  from  a  rarer  into 
a  denser  medium,  if  they  impinge  upon  the  surface  in  a  direc- 
tion removed  from  the  perpendicular,  they  are  bent  out  of  their 
former  direction  towards  that  of  a  line  perpendicular  to  the 
surface  of  the  denser  medium ;  and,  secondly,  by  its  convexity; 
for  it  is  another  law  in  optics  that  rays  of  light  impinging 
upon  a  convex  transparent  surface,  are  refracted  towards  the 
centre,  those  being  most  refracted  which  are  farthest  from  the 
centre  of  the  convex  surface. 

Behind  the  cornea  is  a  space  containing  a  thin  watery  fluid, 
the  aqueous  humor,  holding  in  solution  a  small  quantity  of 
chloride  of  sodium  and  extractive  matter.  The  space  con- 
taining the  aqueous  humor  is  divided  into  an  anterior  and 
posterior  chamber  by  a  membranous  partition,  the  iris,  to  be 
presently  again  mentioned.  The  effect  produced  by  the  aque- 
ous humor  on  the  rays  of  light  traversing  it,  is  not  yet  fully 
ascertained.  Its  chief  use,  probably,  is  to  assist  in  filling  the 
eyeball,  so  as  to  maintain  its  proper  convexity,  and  at  the  same 
time  to  furnish  a  medium  in  which  the  movements  of  the  iris 
can  take  place. 

Behind  the  aqueous  humor  and  the  iris,  and  imbedded  in 


506  THE    SENSE    OF    SIGHT. 

the  anterior  part  of  the  medium  next  to  be  described,  viz.,  the 
vitreous  humor,  is  seated  a  doubly- 
FlG- 183-  convex    body,   the    crystalline   lens, 

which  is  the  most  important  refract- 
ing structure  of  the  eye.  The  struc- 
ture of  the  lens  is  very  complex.  It 
consists  essentially  of  fibres  united 
side  by  side  to  each  other,  and  ar- 
ranged together  in  very  numerous 
laminae,  which  are  so  placed  upon 
one  another,  that  when  hardened  in 
spirit  the  lens  splits  into  three  por- 
tions, in  the  form  of  sectors,  each  of 

Laminated  structure  of  the  ,  .    ;  IP  • 

crystalline  Ions  f -The  lamin*      whlch    1S.  Composed  of  superimposed 
are  split  up  after  hardening  in       Concentric    laming.        The     1«DS     Ill- 
alcohol,  creases  in  density  and,  consequently, 
in  power  of  refraction,  from  without 

inwards ;  the  central  part,  usually  termed  the  nucleus,  being 
the  most  dense.  The  density  of  the  lens  increases  with  age  ; 
it  is  comparatively  soft  in  infancy,  but  very  firm  in  advanced 
life ;  it  is  also  more  spherical  at  an  early  period  of  life  than 
in  old  age. 

The  vitreous  humor  constitutes  nearly  four-fifths  of  the  whole 
globe  of  the  eye.  It  fills  up  the  space  between  the  retina  and 
the  lens,  and  its  soft  jelly-like  substance  consists  essentially 
of  numerous  layers,  formed  of  delicate,  simple  membrane,  the 
spaces  between  which  are  filled  with  a  watery,  pellucid  fluid. 
It  probably  exercises  some  share  in  refracting  the  rays  of  light 
to  the  retina;  but  its  principal  use  appears  to  be  that  of  giv- 
ing the  proper  distension  to  the  globe  of  the  eye,  and  of  keep- 
ing the  surface  of  the  retina  at  a  proper  distance  from  the  lens. 

As  already  observed,  the  space  occupied  by  the  aqueous 
humor  is  divided  into  two  portions  by  a  vertically-placed  mem- 
branous diaphragm,  termed  the  iris,  provided  with  a  central 
aperture,  the  pupil,  for  the  transmission  of  light.  The  iris  is 
composed  of  organic  muscular  fibres  imbedded  in  ordinary 
fibro-cellular  or  connective  tissue.  The  muscular  fibres  of  the 
iris  have  a  direction,  for  the  most  part,  radiating  from  the  cir- 
cumference towards  the  pupil ;  but  as  they  approach  the  pu- 
pillary margin,  they  assume  a  circular  direction,  and  at  the 
very  edge  form  a  complete  ring.  By  the  contraction  of  the 
radiating  fibres,  the  size  of  the  pupil  is  enlarged  :  by  the  con- 
traction of  the  circular  ones,  which  resemble  a  kind  of  sphinc- 
ter, it  is  diminished.  The  object  effected  by  the  movements 
of  the  iris,  is  the  regulation  of  the  quantity  of  light  transmitted 


THE     VITREOUS     HUMOR    AND     IRIS.  507 

to  the  retina;  the  quantity  of  which  is,  cceteris paribus,  directly 
proportioned  to  the  size  of  the  pupillary  aperture.  The  pos- 
terior surface  of  the  iris  is  coated  with  a  layer  of  dark  pig- 
ment, so  that  no  rays  of  light  can  pass  to  the  retina,  except 
such  as  are  admitted  through  the  aperture  of  the  pupil. 

The  ciliary  muscle  is  composed  of  organic  muscular  fibres, 
which  form  a  narrow  zone  around  the  interior  of  the  eyeball, 
near  the  line  of  junction  of  the  cornea  with  the  sclerotic,  and 
just  behind  the  outer  border  of  the  iris  (Fig.  178).  The  outer- 
most fibres  of  this  muscle  are  attached  in  front  to  the  inner 
part  of  the  sclerotic  and  cornea  at  their  line  of  junction,  and, 
diverging  somewhat,  are  fixed  to  the  ciliary  processes,  and  a 
small  portion  of  the  choroid  immediately  behind  them.  The 
inner  fibres,  immediately  within  the  preceding,  form  a  circular 
zone  around  the  interior  of  the  eyeball,  outside  the  ciliary 
processes.  They  compose  the  ring  formerly  called  the  ciliary 
ligament. 

The  function  of  this  muscle  is  to  adapt  the  eye  for  seeing 
objects  at  various  distances.  The  manner  in  which  it  effects 
this  object  will  be  considered  afterwards  (p.  511). 

The  contents  of  the  ball  of  the  eye  are  surrounded  and  kept 
in  position  by  the  cornea,  and  the  dense,  fibrous  membrane 
before  referred  to  as  the  sclerotic,  which,  besides  thus  incasing 
the  contents  of  the  eye,  serves  to  give  attachment  to  the  va- 
rious muscles  by  which  the  movements  of  the  eyeball  are 
effected.  These  muscles,  and  the  nerves  supplying  them,  have 
been  already  considered  (p.  425,  et  seq.}. 

Of  the  Phenomena  of  Vision. 

The  essential  constituents  of  the  optical  apparatus  of  the  eye 
may  be  thus  enumerated :  A  nervous  structure  to  receive  and 
transmit  to  the  brain  the  impressions  of  light ;  certain  refract- 
ing media  for  the  purpose  of  so  disposing  of  the  rays  of  light 
traversing  them  as  to  throw  a  correct  image  of  an  external 
body  on  the  retina ;  a  contractile  diaphragm  with  a  central 
aperture  for  regulating  the  quantity  of  light  admitted  into  the 
eye ;  and  a  contractile  structure  by  which  the  chief  refracting 
medium  shall  be  so  controlled  as  to  enable  objects  to  be  seen 
at  various  distances. 

With  the  help  of  the  diagram  below  (Fig.  184),  represent- 
ing a  vertical  section  of  the  eye  from  before  backwards,  the 
mode  in  which,  by  means  of  the  refracting  media  of  the  eye, 
an  image  of  an  object  of  sight  is  thrown  on  the  retina,  may  be 
rendered  intelligible.  The  rays  of  the  cones  of  light  emitted 
by  the  points  A  B,  and  every  other  point  of  an  object  placed 


508 


THE    SENSE    OF    SIGHT. 


before  the  eye  are  first  refracted,  that  is,  are  bent  towards  the 
axis  of  the  cone,  by  the  cornea  c  c,  and  the  aqueous  humor 
contained  between  it  and  the  lens.  The  rays  of  each  cone  are 


FIG.  184. 


again  refracted  and  bent  still  more  towards  its  central  ray  or 
axis  by  the  anterior  surface  of  the  lens  E  E  ;  and  again,  as 
they  pass  out  through  its  posterior  surface  into  the  less  dense 
medium  of  the  vitreous  humor.  For  a  lens  has  the  power  of 
refracting  and  causing  the  convergence  of  the  rays  of  a  cone 
of  light,  not  only  on  their  entrance  from  a  rarer  medium  into 
its  anterior  convex  surface,  but  also  at  their  exit  from  its  pos- 
terior convex  surface  into  the  rarer  medium. 

In  this  manner  the  rays  of  the  cones  of  light  issuing  from 
the  points  A  and  B  are  again  collected  to  points  at  a  and  b;  and 
if  the  retina  F  be  situated  at  a  and  6,  perfect,  though  reversed, 
images  of  the  points  A  and  B  will  be  perceived ;  but  if  the  ret- 
ina be  not  at  a  and  b,  but  either  before  or  behind  that  situa- 
tion— for  instance,  at  H  or  o — circular  luminous  spots  c,  and  /, 
or  e  and  o,  instead  of  points,  will  be  seen;  for  at  H  the  rays 
have  not  yet  met,  and  at  G  they  have  already  intersected  each 
other,  and  are  again  diverging.  The  retina  must  therefore  be 
situated  at  the  proper  focal  distance  from  the  lens,  otherwise  a 
defined  image  will  not  be  formed  ;  or,  in  other  words,  the  rays 
emitted  by  a  given  point  of  the  object  will  not  be  collected 
into  a  corresponding  point  of  focus  upon  the  retina. 

The  means  by  which  distinct  and  correct  images  of  objects 
are  formed  in  the  retina,  in  the  various  conditions  in  which 
the  eye  is  placed  in  relation  to  external  objects,  may  be  sepa- 
rately considered  under  the  following  heads:  1,  the  means 
for  preventing  indistinctness  from  aberration  ;  2,  the  means 
for  preventing  it  when  objects  are  viewed  at  different  distances; 
3,  the  means  by  which  the  reversed  image  of  an  object  on  the 
retina  is  perceived  as  in  its  right  position  by  the  mind. 


S  P  H  E  R I  C  A  L     A  B  E  R II A  T  I  ()  N.  509 

1.  Since  the  retina  is  concave,  and  from  its  centre  towards 
its  margins  gradually  approaches  the  lens,  it  follows  that  the 
images  of  objects  situated  at  the  sides  cannot  be  so  distinct  as 
those  of  objects  nearer  to  the  middle  of  the  field  of  vision,  and 
of  which  the  images  are  formed  at  a  distance  beyond  the  lens 
exactly  corresponding  to  the  situation  of  the  retina.  More- 
over, the  rays  of  a  cone  of  light  from  an  object  situated  at  the 
side  of  the  field  of  vision  do  not  meet  all  in  the  same  point, 
owing  to  their  unequal  refraction ;  for  the  refraction  of  the 
rays  which  pass  through  the  circumference  of  a  lens  is  greater 
than  that  of  those  traversing  its  central  portion.  The  concur- 
rence of  these  two  circumstances  would  cause  indistinctness  of 
vision,  unless  corrected  by  some  contrivance.  Such  correction 
is  effected,  in  both  cases,  by  the  iris,  which  forms  a  kind  of 
annular  diaphragm  to  cover  the  circumference  of  the  lens,  and 
to  prevent  the  rays  from  passing  through  any  part  of  the  lens 
but  its  centre,  which  corresponds  to  the  pupil. 

The  image  of  an  object  will  be  most  defined  and  distinct 
when  the  pupil  is  narrow,  the  object  at  the  proper  distance  for 
vision,  and  the  light  abundant;  so  that,  while  a  sufficient 
number  of  rays  are  admitted,  the  narrowness  of  the  pupil  may 
prevent  the  production  of  indistinctness  of  the  image  by  this 
spherical  aberration  or  unequal  refraction  just  mentioned. 
But  even  the  image  formed  by  the  rays  passing  through  the 
circumference  of  the  lens,  when  the  pupil  is  much  dilated,  as 
in  the  dark,  or  in  a  feeble  light,  may,  under  certain  circum- 
stances, be  well  defined ;  the  image  formed  by  the  central  rays 
being  then  indistinct  or  invisible,  in  consequence  of  the  retina 
not  receiving  these  rays  where  they  are  concentrated  to  a 
focus.  - 

Distinctness  of  vision,  is  further  secured  by  the  inner  sur- 
face of  the  choroid,  immediately  external  to  the  retina  itself, 
as  well  as  the  posterior  surface  of  the  iris  and  the  ciliary  pro- 
cesses, being  coated  with  black  pigment,  which  absorbs  any 
rays  of  light  that  may  be  reflected  within  the  eye,  and  pre- 
vents their  being  thrown  again  upon  the  retina  so  as  to  inter- 
fere with  the  images  there  formed.  The  pigment  of  the  cho- 
roid is  especially  important  in  this  respect ;  for  the  retina  is 
very  transparent,  and  if  the  surface  behind  it  were  not  of  a 
dark  color,  but  capable  of  reflecting  the  light,  the  luminous 
rays  which  had  already  acted  on  the  retina  would  be  reflected 
again  through  it,  and  would  fall  upon  other  parts  of  the  same 
membrane,  producing  both  dazzling  from  excessive  light,  and 
indistinctness  of  the  images. 

In  the  passage  of  light  through  an  ordinary  convex  lens, 
decomposition  of  each  ray  into  its  elementary  colored  parts 

43 


510  THE    SENSE    OP     SIGHT. 

commonly  ensues,  and  a  colored  margin  appears  around  the 
image,  owing  to  the  unequal  refraction  which  the  elementary 
colors  undergo.  In  the  optical  instruments  this,  which  is 
termed  chromatic  aberration,  is  corrected  by  the  use  of  two  or 
more  lenses,  differing  in  shape  and  density,  the  second  of  which 
continues  or  increases  the  refraction  of  the  rays  produced  by 
the  first,  but  by  recombining  the  individual  parts  of  each  ray 
into  its  original  white  light,  corrects  any  chromatic  aberration 
which  may  have  resulted  from  the  first.  It  is  probable  that 
the  unequal  refractive  power  of  the  transparent  media  in  front 
of  the  retina  may  be  the  means  by  which  the  eye  is  enabled  to 
guard  against  the  effect  of  chromatic  aberration.  The  human 
eye  is  achromatic,  however,  only  so  long  as  the  image  is  re- 
ceived at  its  focal  distance  upon  the  retina,  or  so  long  as  the 
eye  adapts  itself  to  the  different  distances  of  sight.  If  either 
of  these  conditions  be  interfered  with,  a  more  er  less  distinct 
appearance  of  colors  is  produced. 

2.  The  distinctness  of  the  image  formed  upon  the  retina  is 
mainly  dependent  on  the  rays  emitted  by  each  luminous  point 
of  the  object  being  brought  to  a  perfect  focus  upon  the  retina. 
If  this  focus  occur  at  a  point  either  in  front  of,  or  behind  the 
retina,  indistinctness  of  vision  ensues,  with  the  production  of  a 
halo.  The  focal  distance,  i.  e.,  the  distance  of  the  point  at  which 
the  luminous  rays  from  a  lens  are  collected,  besides  being 
regulated  by  the  degree  of  convexity  and  density  of  the  lens, 
varies  with  the  distance  of  the  object  from  the  lens,  being 
greater  as  this  is  shorter,  and  vice  versa.  Hence,  since  objects 
placed  at  various  distances  from  the  eye  can,  within  a  certain 
range,  different  in  different  persons,  be  seen  with  almost  equal 
distinctness,  there  must  be  some  provision  by  which  the  eye  is 
enabled  to  adapt  itself,  so  that  whatever  length  the  focal  dis- 
tance may  be,  the  focal  point  may  always  fall  exactly  upon 
the  retina. 

This  power  of  adaptation  of  the  eye  to  vision  at  different  dis- 
tances has  received  the  most  varied  explanations.  It  is  ob- 
vious that  the  effect  might  be  produced  in  either  of  two  ways, 
viz.,  by  altering  the  convexity  or  density,  and  thus  the  refract- 
ing power,  either  of  the  cornea  or  lens ;  or,  by  changing  the 
position  either  of  the  retina  or  of  the  lens,  so  that  whether  the 
object  viewed  be  near  or  distant,  and  the  focal  distance  thus 
increased  or  diminished,  the  focal  point  to  which  the  rays  are 
converged  by  the  lens  may  always  be  at  the  place  occupied  by 
the  retina.  The  amount  of  either  of  these  changes  required  in 
even  the  widest  range  of  vision,  is  extremely  small.  For,  from 
the  refractive  powers  of  the  media  of  the  eye,  it  has  been  cal- 
culated by  Olbers,  that  the  difference  between  the  focal  dis- 


ADAPTATION    TO    VARIOUS    DISTANCES.       511 

tances  of  the  images  of  an  object  at  such  a  distance  that  the 
rays  are  parallel,  and  of  one  at  the  distance  of  four  inches,  is 
only  about  0.143  of  an  inch.  On  this  calculation,  the  change 
in  the  distance  of  the  retina  from  the  lens  required  for  vision 
at  all  distances,  supposing  the  cornea  and  lens  to  maintain  the 
same  form,  would  not  be  more  than  about  one  line. 

It  is  now  almost  universally  believed  that  Helmholtz  is  right 
in  his  statement  that  the  immediate  cause  of  the  adaptation  of 
the  eye  for  objects  at  different  distances  is  a  varying  shape  of 
the  lens,  its  front  surface  becoming  more  or  less  convex,  accord- 
ing to  the  distance  of  the  object  looked  at.  The  nearer  the 
object,  the  more  convex  does  the  front  surface  of  the  lens  be- 
come, and  vice  versd;  the  back  surface  taking  little  or  no  share 
in  the  production  of  the  effect  required.  Of  course,  the  lens 
has  no  inherent  power  of  contraction,  and  therefore  its  changes 
of  outline  must  be  produced  by  some  power  from  without ;  and 
there  seems  no  reason  to  doubt  that  this  power  is  supplied  by 
the  ciliary  muscle.  The  exact  manner,  however,  in  which,  by 
its  contraction,  the  ciliary  muscle  effects  a  change  in  the  shape 
of  the  crystalline  lens  is  doubtful.  The  most  probable  expla- 
nation of  the  phenomenon,  however,  is  that  in  adapting  the 
eye  for  viewing  near  objects  the  ciliary  muscle  contracts, 
and,  by  such  contraction,  diminishes  the  force  with  which  the 
elastic  suspensory  ligament  of  the  lens  is  tending  to  flatten  it. 
On  the  latter  supposition,  the  lens  may  be  supposed  to  be 
always  in-a  state  of  tension  and  partial  flattening  from  the  ac- 
tion of  the  suspensory  ligament ;  while  the  ciliary  muscle,  by 
diminishing  the  tension  of  this  ligament,  diminishes  to  a  pro- 
portional degree,  the  flattening  of  which  it  is  the  cause.  On 
diminution  or  cessation  of  the  action  of  the  ciliary  muscle,  the 
lens  returns,  in  a  corresponding  degree,  to  its  former  shape,  by 
virtue  of  the  elasticity  of  its  suspensory  ligament.  In  view- 
ing near  objects,  the  iris  contracts,  so  that  its  pupillary  edge 
is  mbved  a  very  little  forwards,  and  the  pupil  itself  is  con- 
tracted— the  opposite  effect  taking  place  on  withdrawal  of  the 
attention  from  near  objects,  and  fixing  it  on  those  distant. 

The  range  of  distances  through  which  persons  can  adapt 
their  power  of  vision  is  not  in  all  cases  the  same.  Some  per- 
sons possess  scarcely  any  power  of  adaptation,  and  of  this  de- 
fect of  vision  there  are  two  kinds ;  one,  in  which  the  person 
can  see  objects  distinctly  only  when  brought  close  to  the  eye, 
having  little  power  to  discern  distant  objects;  another,  in  which 
distant  objects  alone  can  be  distinctly  perceived,  a  small  body 
being  almost  invisible  except  when  held  at  a  considerable 
distance  from  the  eye.  In  the  one  case  the  person  is  said 
to  be  short-sighted  or  myopic :  in  the  other,  long-sighted  or 


512  THE    SENSE    OF    SIGHT. 

presbyopic.  Myopia  is  caused  by  anything,  such  as  undue  con- 
vexity of  the  lens,  which  increases  the  refracting  power  of  the 
eye,  and  so  causes  the  image  of  the  object  to  be  formed  at  a 
point  anterior  to  the  retina :  the  defect  is  remedied  by  the  use 
of  concave  glasses.  Presbyopia,  or  long-sightedness,  is  the 
result  of  conditions  the  reverse  of  the  above,  and  is  remedied 
by  the  use  of  convex  glasses,  which  diminish  the  focal  distance 
of  an  image  formed  in  the  eye.1 

3.  The  direction  given  to  the  rays  by  their  refraction  is  regu- 
lated by  that  of  the  central  ray,  or  axis  of  the  cone,  towards 
which  the  rays  are  bent.  The  image  of  any  point  of  an  object  is, 
therefore,  as  a  rule  (the  exceptions  to  which  need  not  here  be 
stated),  always  formed  in  a  line  identical  with  the  axis  of  the 
cone  of  light,  as  in  the  line  of  B  a,  or  A  b,  Fig.  185  :  so  that  the 
spot  where  the  image  of  any  point  will  be  formed  upon  the  ret- 
ina may  be  determined  by  prolonging  the  central  ray  of  the 
cone  of  light,  or  that  ray  which  traverses  the  centre  of  the 

FIG.  185. 


pupil.  Thus  A  b  is  the  axis  or  central  ray  of  the  cone  of  light 
issuing  from  A ;  B  a,  the  central  ray  of  the  cone  of  light  issuing 
from  B  ;  the  image  of  A  is  formed  at  b,  the  image  of  B  at  a,  in 
the  inverted  position  ;  therefore  what  in  the  object  was  above 
is  in  the  image  below,  and  vice  versd, — the  right  hand  part  of 
the  object  is  in  the  image  to  the  left,  the  left-hand  to  the  right. 
If  an  opening  be  made  in  an  eye  at  its  superior  surface,  so  that 
the  retina  can  be  seen  through  the  vitreous  humor,  this  re- 
versed image  of  any  bright  object,  such  as  the  windows  of  the 
room,  may  be  perceived  at  the  bottom  of  the  eye.  Or  still 
better,  if  the  eye  of  any  albino  animal,  such  as  a  white  rabbit, 
in  which  the  coats,  from  the  absence  of  pigment,  are  transpar- 
ent, is  dissected  clean,  and  held  with  the  cornea  towards  a 
window,  a  very  distinct  image  of  the  window  completely  in- 
verted is  seen  depicted  on  the  posterior  translucent  wall  of  the 

1  For  details  on  this  subject,  consult  the  various  treatises  on  the 
Physiology  and  Defects  of  Vision. 


REVERSION    OF    IMAGE      ON     RETINA.         513 

eye.  Volkrnann  has  also  shown  that  a  similar  experiment  may 
be  successfully  performed  in  a  living  person  possessed  of  large 
prominent  eyes,  and  an  unusually  transparent  sclerotica. 

No  completely  satisfactory  explanation  has  yet  been  offered 
to  account  for  the  mind  being  able  to  form  a  correct  idea  of 
the  erect  position  of  an  object  of  which  an  inverted  image  is 
formed  on  the  retina.  Miiller  and  Volkmann  are  of  opinion 
that  the  mind  really  perceives  an  object  as  inverted,  but  needs 
no  correction,  since  everything  is  seen  alike  inverted,  and  the 
relative  position  of  the  objects  therefore  remains  unchanged ; 
and  the  only  proof  we  can  possibly  have  of  the  inversion  is  by 
experiment  and  the  study  of  the  laws  of  optics.  It  is  the  same 
thing  as  the  daily  inversion  of  objects  consequent  on  the  revo- 
lution of  the  entire  earth,  which  we  know  only  by  observing 
the  position  of  the  stars ;  and  yet  it  is  certain  that,  within 
twenty-four  hours,  that  which  was  below  in  relation  to  the  stars, 
comes  to  be  above.  Hence  it  is,  also,  that  no  discordance 
arises  between  the  sensations  of  inverted  vision  and  those  of 
touch,  which  perceives  everything  in  its  erect  position ;  for  the 
images  of  all  objects,  even  of  our  own  limbs,  in  the  retina,  are 
equally  inverted,  and  therefore  maintain  the  same  relative 
position.  Even  the  image  of  our  hand,  while  used  in  touch, 
is  seen  inverted.  The  position  in  which  we  see  objects,  we  call 
therefore  the  erect  position.  A  mere  lateral  inversion  of  our 
body  in  a  mirror,  where  the  right  hand  occupies  the  left  of  the 
image,  is  indeed  scarcely  remarked  :  and  there  is  but  little 
discordance  between  the  sensations  acquired  by  touch  in  regu- 
lating our  movements  by  the  image  in  the  mirror,  and  those 
of  sight,  as,  for  example,  in  tying  a  knot  in  the  cravat.  There 
is  some  want  of  harmony  here,  on  account  of  the  inversion 
being  only  lateral,  and  not  complete  in  all  directions. 

The  perception  of  the  erect  position  of  objects  appears,  there- 
fore, to  be  the  result  of  an  act  of  the  mind.  And  this  leads  us 
to  a  consideration  of  the  several  other  properties  of  the  retina, 
and  of  the  co-operation  of  the  mind  in  the  several  other  parts 
of  the  act  of  vision.  To  these  belong  not  merely  the  act  of 
sensation  itself,  and  the  perception  of  the  changes  produced 
in  the  retina,  as  light  and  colors,  but  also  the  conversion  of 
the  mere  images  depicted  in  the  retina  into  ideas  of  an  ex- 
tended field  of  vision,  of  proximity  and  distance,  of  the  form 
and. size  of  objects,  of  the  reciprocal  influence  of  different 
parts  of  the  retina  upon  each  other,  the  simultaneous  action  of 
the  two  eyes,  and  some  other  phenomena. 

To  speak  first  of  the  ideal  size  of  the  field  of  vision :  The 
actual  size  of  the  field  of  vision  depends  on  the  extent  of  the 
retina,  for  only  so  many  images  can  be  seen  at  any  one  time 


514  THE    SENSE    OF    SIGHT. 

as  can  occupy  the  retina,  at  the  same  time ;  and  thus  consid- 
ered, the  retina,  of  which  the  affections  are  perceived  by  the 
mind,  is  itself  the  field  of  vision.  But  to  the  mind  of  the 
individual  the  size  of  the  field  of  vision  has  no  determinate 
limits ;  sometimes  it  appears  very  small,  at  another  time  very 
large  ;  for  the  mind  has  the  power  of  projecting  the  images  on 
the  retina  towards  the  exterior.  Hence  the  mental  field  of 
vision  is  very  small  when  the  sphere  of  the  action  of  the  mind 
is  limited  to  impediments  near  the  eye :  on  the  contrary,  it  is 
very  extensive  when  the  projection  of  the  images  on  the  retina 
towards  the  exterior,  by  the  influence  of  the  mind,  is  not  im- 
peded. It  is  very  small  when  we  look  into  a  hollow  body  of 
small  capacity  held  before  the  eyes  ;  large  when  we  look  out 
upon  the  landscape  through  a  small  opening  ;  more  extensive 
when  we  look  at  the  landscape  through  a  window  ;  and  most 
so  when  our  view  is  not  confined  by  any  near  object.  In  all 
these  cases  the  idea  which  we  receive  of  the  size  of  the  field  of 
vision  is  very  different,  although  its  absolute  size  is  in  all  the 
same,  being  dependent  on  the  extent  of  the  retina.  Hence  it 
follows,  that  the  mind  is  constantly  co-operating  in  the  acts  of 
vision,  so  that  at  last  it  becomes  difficult  to  say  what  belongs 
to  mere  sensation,  and  what  to  the  influence  of  the  mind. 

By  a  mental  operation  of  this  kind,  we  obtain  a  correct  idea 
of  the  size  of  individual  objects,  as  well  as  of  the  extent  of  the 
field  of  vision.  To  understand  this,  it  will  be  necessary  to 
refer  again  to  Fig.  185,  p.  512. 

The  angle  x,  included  between  the  decussating  central  rays 
of  two  cones  of  light  issuing  from  different  points  of  an  object, 
is  called  the  optical  angle — angulus  opticus  sen  visorim.  This 
angle  becomes  larger,  the  greater  the  distance  between  the 
points  A  and  B  ;  and  since  the  angles  x  and  y  are  equal,  the 
distance  between  the  points  a  and  6  in  the  image  on  the  retina 
increases  as  the  angle  x  becomes  larger.  Objects  at  different 
distances  from  the  eye,  but  having  the  same  optical  angle,  x 
— for  example,  the  objects,  c,  d,  and  e, — must  also  throw 
images  of  equal  size  upon  the  retina ;  and  if  they  occupy  the 
same  angle  of  the  field  of  vision,  their  image  must  occupy  the 
same  spot  in  the  retina. 

Nevertheless,  these  images  appear  to  the  mind  to  be  of  very 
unequal  size  when  the  ideas  of  distance  and  proximity  come 
into  play ;  for  from  the  image  a  b,  the  mind  forms  the  concep- 
tion of  a  visual  space  extending  to  e,  d,  or  c,  and  of  an  object 
of  the  size  which  that  represented  by  the  image  on  the  retina 
appears  to  have  when  viewed  close  to  the  eye,  or  under  the 
most  usual  circumstances.  A  landscape  depicted  on  the 
retina,  as  a  b,  and  viewed  under  the  angle  x,  is  therefore  con- 


VISUAL    DIRECTION.  515 

ceived  by  the  mind  to  have  an  extent  of  two  miles  perhaps,  if 
we  know  that  its  extent  is  such,  or  if  we  infer  it  to  be  so  from 
the  number  of  known  objects  seen  at  the  same  time.  And  in 
the  same  way  that  the  images  of  several  different  objects, 
viewed  under  the  same  angle,  thus  appears  to  the  mind  to  have 
a  different  size  in  the  field  of  vision,  so  the  whole  field  of  vision 
which  has  always  the  same  absolute  size,  is  interpreted  by  the 
mind  as  of  extremely  various  extent ;  and  for  this  reason  also, 
the  image  viewed  in  the  camera  obscura  is  regarded  as  a  real 
landscape — as  the  true  field  of  vision — although  only  a  small 
image  depicted  upon  paper.  The  same  mental  process  gives 
rise  to  the  idea  of  depth  in  the  field  of  vision  ;  this  idea 
being  fixed  in  our  mind  principally  by  the  circumstance  that, 
as  we  ourselves  move  forward,  different  images  in  succession 
become  depicted  on  our  retina,  so  that  we  seem  to  pass  be- 
tween these  images,  which  to  the  mind  is  the  same  thing  as 
passing  between  the  objects  themselves. 

The  action  of  the  sense  of  vision  in  relation  to  external 
objects  is,  therefore,  quite  different  from  that  of  the  sense  of 
touch.  The  objects  of  the  latter  sense  are  immediately  pres- 
ent to  it ;  and  our  own  body,  with  which  they  come  into  con- 
tact, is  the  measure  of  their  size.  The  part  of  a  table  touched 
by  the  hand  appears  as  large  as  the  part  of  the  hand  receiv- 
ing an  impression  from  it,  for  a  part  of  our  body  in  which  a 
sensation  is  excited  is  here  the  measure  by  which  we  judge  of 
the  magnitude  of  the  object.  In  the  sense  of  vision,  on  the 
contrary,  the  images  of  objects  are  mere  fractions  of  the  objects 
themselves  realized  upon  the  retina,  the  extent  of  which  re- 
mains constantly  the  same.  But  the  imagination,  which  ana- 
lyzes the  sensations  of  vision,  invests  the  images  of  objects, 
together  with  the  whole  field  of  vision  in  the  retina,  with  very 
varying  dimensions ;  the  relative  size  of  the  images  in  propor- 
tion to  the  whole  field  of  vision,  or  of  the  affected  parts  of  the 
retina  to  the  whole  retina,  alone  remaining  unaltered. 

The  direction  in  which  an  object  is  seen,  the  direction  of 
vision,  or  visual  direction,  depends  on  the  part  of  the  retina 
which  receives  the  image,  and  on  the  distance  of  this  part 
from,  and  its  relation  to,  the  central  point  of  the  retina.  Thus, 
objects  of  which  the  images  fall  upon  the  same  parts  of  the 
retina  lie  in  the  same  visual  direction  ;  and  when,  by  the  action 
of  the  mind,  the  images  or  affections  of  the  retina  are  projected 
into  the  exterior  world,  the  relation  of  the  images  to  each 
other  remains  the  same. 

The  estimation  of  the  form  of  bodies  by  sight  is  the .  result 
partly  of  the  mere  sensation,  and  partly  of  the  association  of 
ideas.  Since  the  form  of  the  images  perceived  by  the  retina 


516  THE    SENSE    OF    SIGHT. 

depends  wholly  on  the  outline  of  the  part  of  the  retina  affected, 
the  sensation  alone  is  adequate  to  the  distinction  of  only  su- 
perficial forms  of  each  other,  as  of  a  square  from  a  circle.  But 
the  idea  of  a  solid  body,  as  a  sphere,  or  a  body  of  three  or 
more  dimensions,  e.  g.,  a  cube,  can  only  be  attained  by  the  ac- 
tion of  the  mind  constructing  it  from  the  different  superficial 
images  seen  in  different  positions  of  the  eye  with  regard  to  the 
object;  and,  as  shown  by  Mr.  Wheatstone  and  illustrated  in 
the  stereoscope,  from  two  different  perspective  projections  of 
the  body  being  presented  simultaneously  to  the  mind  by  the 
two  eyes.  Hence,  when,  in  adult  age,  sight  is  suddenly  re- 
stored to  persons  blind  from  infancy,  all  objects  in  the  field  of 
vision  appear  at  first  as  if  painted  flat  on  one  surface ;  and  no 
idea  of  solidity  is  formed  until  after  long  exercise  of  the  sense 
of  vision  combined  with  that  of  touch. 

We  judge  of  the  motion  of  an  object,  partly  from  the  motion 
of  its  image  over  the  surface  of  the  retina,  and  partly  from 
the  motion  of  our  eyes  following  it.  If  the  image  upon  the 
retina  moves  while  our  eyes  and  our  body  are  at  rest,  we  con- 
clude that  the  object  is  changing  its  relative  position  with  re- 
gard to  ourselves.  In  such  a  case  the  movement  of  the  object 
may  be  apparent  only,  as  when  we  are  standing  upon  a  body 
which  is  in  motion,  such  as  a  ship.  If,  on  the  other  hand,  the 
image-  does  not  move  with  regard  to  the  retina,  but  remains 
fixed  upon  the  same  spot  of  that  membrane,  while  our  eyes 
follow  the  moving  body,  we  judge  of  the  motion  of  the  object 
by  the  sensation  of  the  muscles  in  action  to  move  the  eye.  If 
the  image  moves  over  the  surface  of  the  retina  while  the  mus- 
cles of  the  eye  are  acting  at  the  same  time  in  a  manner  cor- 
responding to  this  motion,  as  in  reading,  we  infer  that  the  ob- 
ject is  stationary,  and  we  know  that  we  are  merely  altering 
the  relations  of  our  eyes  to  the  object.  Sometimes  the  object 
appears  to  move  when  both  object  and  eye  are  fixed,  as  in 
vertigo. 

The  mind  can,  by  the  faculty  of  attention,  concentrate  its  ac- 
tivity more  or  less  exclusively  upon  the  senses  of  sight,  hear- 
ing, and  touch  alternately.  When  exclusively  occupied  with 
the  action  of  one  sense,  it  is  scarcely  conscious  of  the  sensations 
of  the  others.  The  mind,  when  deeply  immersed  in  contem- 
plations of  another  nature,  is  indifferent  to  the  actions  of  the 
sense  of  sight,  as  of  every  other  sense.  We  often,  when  deep 
in  thought,  have  our  eyes  open  and  fixed,  but  see  nothing,  be- 
cause of  the  stimulus  of  ordinary  light  being  unable  to  excite 
the  mind  to  perception  when  otherwise  engaged.  The  atten- 
tion which  is  thus  necessary  for  vision,  is  necessary  also  to 


ANALYSIS    OF     FIELD    OF     VISION.  517 

analyze  what  the  field  of  vision  presents.  The  mind  does  not 
perceive  all  the  objects  presented  by  the  field  of  vision  at  the 
same  time  with  equal  acuteness,  but  directs  itself  first  to  one 
and  then  to  another.  The  sensation  becomes  more  intense, 
according  as  the  particular  object  is  at  the  time  the  principal 
object  of  mental  contemplation.  Any  compound  mathematical 
figure  produces  a  different  impression  according  as  the  attention 
is  directed  exclusively  to  one  or  the  other  part 
of  it.  Thus,  in  Fig.  186,  we  may  in  succession  FlG-  186- 
have  a  vivid  perception  of  the  whole,  or  of  dis- 
tinct parts  only  ;  of  the  six  triangles  near  the 
outer  circle,  of  the  hexagon  in  the  middle,  or 
of  the  three  large  triangles.  The  more  nume- 
rous and  varied  the  parts  of  which  a  figure  is 
composed,  the  more  scope  does  it  afford  lor  the 
play  of  the  attention.  Hence  it  is  that  architectural  orna- 
ments have  an  enlivening  effect  on  the  sense  of  vision,  since 
they  afford  constantly  fresh  subject  for  the  action  of  the  mind. 

The  duration  of  the  sensation  produced  by  a  luminous 
impression  on  the  retina  is  always  greater  than  that  of  the 
impression  which  produces  it.  However  brief  the  luminous 
impression,  the  effect  on  the  retina  always  lasts  for  about  one- 
eighth  of  a  second.  Thus,  supposing  an  object  in  motion,  say 
a  horse,  to  be  revealed  on  a  dark  night  by  a  flash  of  lightning. 
The  object  would  be  seen  apparently  for  an  eighth  of  a  second, 
but  it  would  not  appear  in  motion ;  because,  although  the 
image  remained  on  the  retina  for  this  time,  it  was  really  re- 
vealed for  such  an  extremely  short  period  (the  duration  of  a 
flash  of  lightning  being  almost  instantaneous),  that  no  appre- 
ciable movement  on  the  part  of  the  object  could  have  taken 
place  in  the  period  during  which  it  was  revealed  to  the  retina 
of  the  observer.  And  the  same  fact  is  proved  in  a  reverse 
wray.  The  spokes  of  a  rapidly  revolving  wheel  are  not  seen 
as  distinct  objects,  because  at  every  point  of  the  field  of  vision 
over  which  the  revolving  spokes  pass,  a  given  impression  has 
not  faded  before  another  comes  to  replace  it.  Thus  every  part 
of  the  interior  of  the  wheel  appears  occupied. 

The  duration  of  the  after  sensation  or  spectrum,  produced  by 
an  object,  is  greater  in  a  direct  ratio  with  the  duration  of  the 
impression  which  caused  it.  Hence  the  image  of  a  bright 
object,  as  of  the  panes  of  a  window  through  which  the  light 
is  shining,  may  be  perceived  in  the  retina  for  a  considerable 
period,  if  we  have  previously  kept  our  eye  fixed  for  some  time 
on  it. 

The  color  of  the  spectrum  varies  with  that  of  the  object 
which  produced  it.  The  spectra  left  by  the  images  of  white  or 

44 


518 


THE    SENSE    OF    SIGHT. 


luminous  objects,  are  ordinarily  white  or  luminous ;  those  left 
by  dark  objects  are  dark.  Sometimes,  however,  the  relation 
of  the  light  and  dark  parts  in  the  image  may,  under  certain 
circumstances,  be  reversed  in  the  spectrum  ;  what  was  bright 
may  be  dark,  and  what  was  dark  may  appear  light.  This 
occurs  whenever  the  eye,  which  is  the  seat  of  the  spectrum  of 

FIG.  187. 


A  circle  showing  the  various  simple  and  compound  colors  of  light,  and  those 
which  are  complemental  of  each  other,  i.e.,  which,  when  mixed,  produce  a  neutral 
gray  tint.  The  three  simple  colors,  red,  yellow,  and  blue,  are  placed  at  the  angles 
of  an  equilateral  triangle  ;  which  are  connected  together  by  means  of  a  circle ;  the 
mixed  colors,  green,  orange,  and  violet,  are  placed  intermediate  between  the  cor- 
responding simple  or  homogeneous  colors ;  and  the  complemental  colors,  of  which 
the  pigments,  when  mixed,  would  constitute  a  gray,  and  of  which  the  prismatic 
spectra  would  together  produce  a  white  light,  will  be  found  to  b3  placed  in  each  case 
opposite  to  each  other,  but  connected  by  a  line  passing  through  the  centre  of  the 
circle.  The  figure  is  also  useful  in  showing  the  further  shades  of  color  which  are 
complementary  of  each  other.  If  the  circle  be  supposed  to  contain  every  transition 
of  color  between  the  six  marked  down,  those  which,  when  united,  yield  a  white  or 
gray  color,  will  always  be  found  directly  opposite  to  each  other;  thus,  for  example, 
the  intermediate  tint  between  orange  or  red  is  complemental  of  the  middle  tint 
between  green  and  blue. 

a  luminous  object,  is  not  closed,  but  fixed  upon  another  bright 
or  white  surface,  as  a  white  wall,  or  a  sheet  of  white  paper. 
Hence  the  spectrum  of  the  sun,  which,  while  light  is  excluded 
from  the  eye  is  luminous,  appears  black  or  gray  when  the  eye 
is  directed  upon  a  white  surface.  The  explanation  of  this  is, 
that  the  part  of  the  retina  which  has  received  the  luminous 
image  remains  for  a  certain  period  afterwards  in  an  exhausted 
or  less  sensitive  state,  while  that  which  has  received  a  dark 
image  is  in  an  unexhausted,  and  therefore  much  more  excitable 
condition. 

The  ocular  spectra  which  remain  after  the  impression  of 
colored  objects  upon  the  retina  are  always  colored ;  and  their 
color  is  not  that  of  the  object,  or  of  the  image  produced  di- 
rectly by  the  object,  but  the  opposite,  or  complemental  color. 
The  spectrum  of  a  red  object  is,  therefore,  green ;  that  of  a 


COMPLEMENTARY     COLORS.  519 

green  object,  red ;  that  of  violet,  yellow ;  that  of  yellow,  violet, 
and  so  on.  The  reason  of  this  is  obvious.  The  part  of  the 
retina  which  receives,  say,  a  red  image,  is  wearied  by  that 
particular  color,  but  remains  sensitive  to  the  other  rays  which 
with  red  make  up  white  light ;  and,  therefore,  these  by  them- 
selves reflected  from  a  white  object  produce  a  green  hue.  If, 
on  the  other  hand,  the  first  object  looked  at  be  green,  the 
retina,  being  tired  of  green  rays,  receives  a  red  image  when 
the  eye  is  turned  to  a  white  object.  And  so  with  the  other 
colors;  the  retina  while  fatigued  by  yellow  rays  will  suppose  an 
object  to  be  violet,  and  vice  versd;  the  size  and  shape  of  the 
spectrum  corresponding  with  the  size  and  shape  of  the  original 
object  looked  at.  The  colors  which  thus  reciprocally  excite 
each  other  in  the  retina  are  those  placed  at  opposite  points 
of  the  circle  in  Fig.  187. 

Of  the  Reciprocal  Action  of  different  Parts  of  the  Retina  on 
each  other. 

Although  each  elementary  part  of  the  retina  represents  a 
distinct  portion  of  the  field  of  vision,  yet  the  different  elemen- 
tary parts,  or  sensitive  points,  of  that  membrane  have  a  certain 
influence  on  each  other ;  the  particular  condition  of  one  in- 
fluencing that  of  another,  so  that  the  image  perceived  by  one 
part  is  modified  by  the  image  depicted  in  the  other.  The 
phenomena,  which  result  from  this  relation  between  the  dif- 
ferent parts  of  the  retina,  may  be  arranged  in  two  classes ;  the 
one  including  those  where  the  condition  existing  in  the  greater 
extent  of  the  retina  is  imparted  to  the  remainder  of  that  mem- 
brane ;  the  other,  consisting  of  those  in  which  the  condition  of 
the  larger  portion  of  the  retina  excites,  in  the  less  extensive 
portion,  the  opposite  condition. 

1.  When  two  opposite  impressions  occur  in  contiguous  parts 
of  an  image  on  the  retina,  the  one  impression  is,  under  certain 
circumstances,  modified  by  the  other.  If  the  impressions  oc- 
cupy each  one-half  of  the  image,  this  does  not  take  place ;  for 
in  that  case,  their  actions  are  equally  balanced.  But  if  one 
of  the  impressions  occupies  only  a  small  part  of  the  retina,  and 
the  other  the  greater  part  of  its  surface,  the  latter  may,  if  long 
continued,  extend  its  influence  over  the  whole  retina,  so  that 
the  opposite  less  extensive  impression  is  no  longer  perceived, 
and  its  place  becomes  occupied  by  the  same  sensation  as  the 
rest  of  the  field  of  vision.  Thus,  if  we  fix  the  eye  for  some 
time  upon  a  strip  of  colored  paper  lying  upon  a  white  surface, 
the  image  of  the  colored  object,  especially  when  it  falls  on  the 


520  THE    SENSE    OF    SIGHT. 

lateral  parts  of  the  retina,  will  gradually  disappear,  and  the 
white  surface  be  seen  in  its  place. 

2.  In  the  second  class  of  phenomena,  the  affection  of  one 
part  of  the  retina  influences  that  of  another  part,  not  in 
such  a  manner  as  to  obliterate  it,  but  so  as  to  cause  it  to  be- 
come the  contrast  or  opposite  of  itself.  Thus  a  gray  spot  upon  a 
white  ground  appears  darker  than  the  same  tint  of  gray  would 
do  if  it  alone  occupied  the  whole  field  of  vision,  and  a  shadow 
is  always  rendered  deeper  when  the  light  which  gives  rise  to  it 
becomes  more  intense,  owing  to  the  greater  contrast.  The 
former  phenomena  ensue  gradually,  and  only  after  the  images 
have  been  long  fixed  on  the  retina;  the  latter  are  instantaneous 
in  their  production,  and  are  permanent. 

In  the  same  way,  also,  colors  may  be  produced  by  contrast. 
Thus,  a  very  small  dull-gray  strip  of  paper,  lying  upon  an  ex- 
tensive surface  of  any  bright  color,  does  not  appear  gray,  but 
has  a  faint  tint  of  the  color  which  is  the  complement  of  that 
of  the  surrounding  surface  (seepage  519).  A  strip  of  gray 
paper  upon  a  green  field,  for  example,  often  appears  to  have 
a  tint  of  red,  and  when  lying  upon  a  red  surface,  a  greenish 
tint ;  it  has  an  orange-colored  tint  upon  a  bright  blue  surface, 
and  a  bluish  tint  upon  an  orange-colored  surface ;  a  yellowish 
color  upon  a  bright  violet,  and  a  violet  tint  upon  a  bright 
yellow  surface.  The  color  excited  thus,  as  a  contrast  to  the 
exciting  color,  being  wholly  independent  of  any  rays  of  the 
corresponding  color  acting  from  without  upon  the  retina,  must 
arise  as  an  opposite  or  antagonistic  condition  of  that  mem- 
brane ;  and  the  opposite  conditions  of  which  the  retina  thus 
becomes  the  subject  would  seem  to  balance  each  other  by  their 
reciprocal  reaction.  A  necessary  condition  for  the  production 
of  the  contrasted  colors  is,  that  the  part  of  the  retina  in  which 
the  new  color  is  to  be  excited,  shall  be  in  a  state  of  compara- 
tive repose ;  hence  the  small  object  itself  must  be  gray.  A 
second  condition  is,  that  the  color  of  the  surrounding  surface 
shall  be  very  bright,  that  is,  it  shall  contain  much  white  light. 

The  retina  corresponding  to  the  point  of  entrance  of  the 
optic  nerve  is  completely  insensible  to  the  impressions  of  light. 
The  phenomenon  itself  is  very  readily  shown.  If  we  direct 
one  eye,  the  other  being  closed,  upon  a  point  at  such  a  distance 
to  the  side  of  any  object,  that  the  image  of  the  latter  must 


fall  upon  the  retina  at  the  point  of  entrance  of  the  optic  nerve, 
this  image  is  lost  either  instantaneously,  or  very  soon.     If,  for 


SINGLE    VISION.  521 

example,  we  close  the  left  eye,  and  direct  the  axis  of  the  right 
eye  steadily  towards  the  circular  spot  above  represented,  while 
the  page  is  held  at  a  distance  of  about  six  inches  from  the 
eye,  both  dot  and  cross  are  visible.  On  gradually  increasing 
the  distance  between  the  eye  and  the  object,  by  removing  the 
book  farther  and  farther  from  the  face,  and  still  keeping  the 
right  eye  steadily  on  the  dot,  it  will  be  found  that  suddenly 
the  cross  disappears  from  view,  while  on  removing  the  book 
still  farther,  it  suddenly  comes  in  sight  again.  The  cause  of 
this  phenomenon  is  simply  that  the  portion  of  retina  which  is 
occupied  by  the  entrance  of  the  optic  nerve,  is  quite  blind ; 
and  therefore  that  when  it  alone  occupies  the  field  of  vision, 
objects  cease  to  be  visible. 

Of  the  Simultaneous  Action  of  the  two  Eyes. 

Although  the  sense  of  sight  is  exercised  by  two  organs,  yet 
the  impression  of  an  object  conveyed  to  the  mind  is  single. 
Various  theories  have  been  advanced  to  account  for  this  phe- 
nomenon. By  Gall,  it  was  supposed  that  we  do  not  really 
employ  both  eyes  simultaneously  in  vision,  but  always  see  with 
only  one  at  a  time.  This  especial  employment  of  one  eye  in 
vision  certainly  occurs  in  persons  whose  eyes  are  of  very  un- 
equal focal  distance,  but  in  the  majority  of  individuals  both 
eyes  are  simultaneously  in  action  in  the  perception  of  the  same 
object ;  this  is  shown  by  the  double  images  seen  under  certain 
conditions.  If  two  fingers  be  held  up  before  the  eyes,  one  in 
front  of  the  other,  and  vision  be  directed  to  the  more  distant, 
so  that  it  is  seen  singly,  the  nearer  will  appear  double ;  while, 
if  the  nearer  one  be  regarded,  the  most  distant  will  be  seen 
double ;  and  one  of  the  double  images  in  each  case  will  be 
found  to  belong  to  one  eye,  the  other  to  the  other  eye. 

Single  vision  results  only  when  certain  parts  of  the  two 
retinae  are  affected  simultaneously ;  if  different  parts  of  the 
retinae  receive  the  image  of  the  object,  it  is  seen  double.  The 
parts  of  the  retinae  in  the  two  eyes  which  thus  correspond  to 
each  other  in  the  property  of  referring  the  images  which  affect 
them  simultaneously  to  the  same  spot  in  the  field  of  vision  are, 
in  man,  just  those  parts  which  would  correspond  to  each  other, 
if  one  retina  were  placed  exactly  in  front  of,  and  over  the 
other  (as  in  Fig.  188,  c).  Thus,  the  outer  lateral  portion  of 
one  eye  corresponds  to,  or,  to  use  a  better  term,  is  identical 
with  the  inner  portion  of  the  other  eye ;  or  a  of  the  eye  A 
(Fig.  188)  with  a'  of  the  eye  B.  The  upper  part  of  one  retina 
is  also  identical  with  the  upper  part  of  the  other ;  and  the  lower 
parts  of  the  two  eyes  are  identical  with  each  other. 


522  THE    SENSE    OF    SIGHT. 

This  is  proved  by  a  single  experiment.     Pressure  upon  any 
part  of  the  ball  of  the  eye,  so  as  to  affect  the  retina,  produces 

a  luminous  circle,  seen  at  the 
FIG.  IBS.  opposite  side  of  the  field  of 

vision  to  that  on  which  the 
pressure  is  made.  If,  now,  in 
a  dark  room,  we  press  with 
the  finger  at  the  upper  part 
of  one  eye,  and  at  the  lower 
part  of  the  other,  two  lumin- 
ous circles  are  seen,  one  above 
the  other;  so,  also,  two  figures 
are  seen  when  pressure  is  made 
simultaneously  on  the  two  outer  or  the  two  inner  sides  of  both 
eyes.  It  is  certain,  therefore,  that  neither  the  upper  part  of 
one  retina  and  the  lower  part  of  the  other  are  identical,  nor 
the  outer  lateral  parts  of  the  two  retinae,  nor  their  inner  lateral 
portions.  But  if  pressure  be  made  with  the  fingers  upon  both 
eyes  simultaneously  at  their  lower  part,  one  luminous  ring  is 
seen  at  the  middle  of  the  upper  part  of  the  field  of  vision ;  if 
the  pressure  be  applied  to  the  upper  part  of  both  eyes,  a  single 
luminous  circle  is  seen  in  the  middle  of  the  field  of  vision 
below.  So,  also,  if  we  press  upon  the  outer  side  a  of  the  eye 
A,  and  upon  the  inner  side  a'  of  the  eye  B,  a  single  spectrum 
is  produced,  and  is  apparent  at  the  extreme  right  of  the  field 
of  vision ;  if  upon  the  point  b  of  one  eye,  and  the  point  b'  of 
the  other,  a  single  spectrum  is  seen  to  the  extreme  left. 

The  spheres  of  the  two  retinae  may,  therefore,  be  regarded 
as  lying  one  over  the  other,  as  in  c,  Fig.  188 ;  so  that  the  left 
portion  of  one  eye  lies  over  the  identical  left  portion  of  the 
other  eye,  the  right  portion  of  one  eye  over  the  identical  right 
portion  of  the  other  eye ;  and  with  the  upper  and  lower  por- 
tions of  the  two  eyes,  a  lies  over  a',  b  over  b',  and  c  over  c'. 
The  points  of  the  one  retina  intermediate  between  a  and  c,  are 
again  identical  writh  the  corresponding  points  of  the  other 
retina  between  a'  and  c' ;  those  between  b  and  c  of  the  one 
retina,  with  those  between  b'  and  c'  of  the  other.  In  short,  all 
other  parts  are  non-identical :  and,  when  they  are  excited  to 
action,  the  effect  is  the  same  as  if  the  impressions  were  made 
on  different  parts  of  the  same  retina :  and  the  double  images 
belonging  to  the  eyes  A  and  B,  are  seen  at  exactly  the  same 
distance  from  each  other  as  exists  between  the  image  of  the 
eye  A  and  the  part  of  the  retina  of  the  eye  A  which  corre- 
sponds to,  or  is  identical  with,  the  seat  of  the  second  image  in 
the  eye  B ;  or,  to  return  to  the  figure  already  used  in  illustra- 
tion (Fig.  188),  if  a  of  one  eye  be  affected,  and  b'  of  the  other, 


SINGLE    VISION.  523 

the  distances  of  the  two  images  a  and  b'  will,  inasmuch  as  a  is 
identical  with  a',  and  b'  with  b,  lie  at  exactly  the  same  distance 
from  each  other  as  images  produced  by  impressions  on  the 
points  a  b  of  the  one  eye,  or  a'  b'  of  the  other. 

In  application  of  these  results  to  the  phenomena  of  vision, 
if  the  position  of  the  eyes  with  regard  to  a  luminous  object 
be  such  that  similar  images  of  the  same  object  fall  on  identi- 
cal parts  of  the  two  retinse,  as  occurs  when  the  axes  meet  in 
some  one  point,  the  object  is  seen  single ;  if  otherwise,  as  in 
the  various  forms  of  squinting,  two  images  are  formed,  and 
double  vision  results.  If  the  axes  of  the  eyes,  A  and  B  (Fig. 
189),  be  so  directed  that  they  meet  at  a,  an  object  at  a  will 
be  seen  singly,  for  the  point  a  of  the  one  retina,  and  a'  of  the 
other,  are  identical.  So,  also,  if  the  object  /?  be  so  situated 
that  its  image  falls  in  both  eyes  at  the  same  distance  from  the. 
central  point  of  the  retina, — namely,  at  b  in  the  one  eye,  and 
at  b'  in  the -other, — /9will  be  seen  single,  for  it  affects  identical 
parts  of  the  two  retinse.  The  same  will  apply  to  the  object  /. 

In  quadrupeds,  the  relation  between  the  identical  and  non- 
identical  parts  of  the  retinse  cannot  be  the  same  as  in  man  ; 

FIG.  189. 


for  the  axes  of  their  eyes  generally  diverge,  and  can  never  be 
made  to  meet  in  one  point  of  an  object.  When  an  animal  re- 
gards an  object  situated  directly  in  front  of  it,  the  image  of 
the  object  must  fall,  in  both  eyes,  on  the  outer  portion  of  the 
retiuse.  Thus  the  image  of  the  object  a  (Fig.  191)  will  fall  at 
a'  in  one,  and  at  a"  in  the  other :  and  these  points  a'  and  a" 
must  be  identical.  So,  also,  for  distinct  and  single  vision  of 
objects,  b  or  c,  the  points  b'  and  b",  or  c'  c",  in  the  two  retinse, 


524 


THE    SENSE    OF    SIGHT. 


on  which  the  images  of  these  objects  fall,  must  be  identical. 
All  points  of  the  retina  in  each  eye  which  receive  rays  of  light 
from  lateral  objects  only,  can  have  no  corresponding  identi- 
cal points  in  the  retina  of  the  other  eye ;  for  otherwise  two  ob- 
jects, one  situated  to  the  right  and  the  other  to  the  left,  would 
appear  to  lie  in  the  same  spot  of  the  field  of  vision.  It  is 
probable,  therefore,  that  there  are,  in  the  eyes  of  animals, 
parts  of  the  retinse  which  are  identical,  and  parts  which  are 
not  identical,  i.  e.,  parts  in  one  which  have  no  corresponding 
parts  in  the  other  eye.  And  the  relation  of  the  retinse  to  each 
other  in  the  field  of  vision  may  be  represented  as  in  Fig.  190. 
The  cause  of  the  impressions  on  the  identical  points  of  the 
two  retinse  giving  rise  to  but  one  sensation,  and  the  perception 
of  a  single  image,  must  either  lie  in  the  structural  organization 
of  the  deeper  or  cerebral  portion  of  the  visual  apparatus,  or 
be  the  result  of  a  mental  operation ;  for  in  no  other  case  is  it 
the  property  of  the  corresponding  nerves  of  the  two  sides  of 
the  body  to  refer  their  sensations  as  one  to  one  spot. 


FIG.  190. 


Many  attempts  have  been  made  to  explain  this  remarkable 
relation  between  the  eyes,  by  referring  it  to  anatomical  rela- 
tion between  the  optic  nerves.  The  circumstance  of  the  inner 
portion  of  the  fibres  of  the  two  optic  nerves  decussating  at  the 
commissure,  and  passing  to  the  eye  of  the  opposite  side,  while 
the  outer  portion  of  the  fibres  continue  their  course  to  the  eye 
of  the  same  side,  so  that  the  left  side  of  both  retinae  is  formed 
from  one  root  of  the  nerves,  and  the  right  side  of  both  retinse 
from  the  other  root,  naturally  lead  to  an  attempt  to  explain 


SINGLE    VISION. 


525 


the  phenomenon  by  this  distribution  of  the  fibres  of  the  nerves. 
And  this  explanation  is  favored  by  cases  in  which  the  entire 
of  one  side  of  the  retina,  as  far  as  the  central  point  in  both 
eyes,  sometimes  becomes  insensible.  But  Miiller  shows  the 
inadequateness  of  this  theory  to  explain  the  phenomenon,  un- 
less it  be  supposed  that  each  fibre  in  each  cerebral  portion  of 
the  optic  nerves  divides  in  the  optic  commissure  into  two 
branches  for  the  identical  points  of  the  two  retinae,  as  is  shown 
in  Fig.  192.  But  there  is  no  foundation  for  such  supposition. 
By  another  theory  it  is  assumed  that  each  optic  nerve  con- 
tains exactly  the  same  number  of  fibres  as  the  other,  and  that 
the  corresponding  fibres  of  the  two  nerves  are  united  in  the 
sensorium  (as  in  Fig.  193).  But  in  this  theory  no  account  is 


FIG.  192. 


FIG.  193. 


FIG.  194. 


taken  of  the  partial  decussation  of  the  fibres  of  the  nerves  in 
the  optic  commissure. 

According  to  a  third  theory,  the  fibres  a  and  a',  Fig.  194, 
coming  from  identical  points  of  the  two  retinse,  are  in  the 
optic  commissure  brought  into  one  optic  nerve,  and  in  the 
brain  either  are  united  by  a  loop,  or  spring  from  the  same 
point.  The  same  disposition  prevails  in  the  case  of  the  iden- 
tical fibres  b  and  b'.  According  to  this  theory,  the  left  half 
of  each  retina  would  be  represented  in  the  left  hemisphere  of 
the  brain,  and  the  right  half  of  each  retina  in  the  right  hem- 
isphere. 

Another  explanation  is  founded  on  the  fact,  that  at  the 
anterior  part  of  the  commissure  of  the  optic  nerve,  certain 
fibres  pass  across  from  the  distal  portion  of  one  nerve  to  the 
corresponding  portion  of  the  other  nerves,  as  if  they  were  com- 
missural  fibres  forming  a  connection  between  the  retinae  of  the 
two  eyes.  It  is  supposed,  indeed,  that  these  fibres  may  con- 
nect the  corresponding  parts  of  the  two  retinse,  and  may  thus 
explain  their  unity  of  action  ;  in  the  same  way  that  corre- 
sponding parts  of  the  cerebral  hemispheres  are  believed  to  be 


526 


THE    SENSE    OF    SIGHT. 


connected   together  by  the  commissural  fibres  of  the  corpus 
callosum,  and  so  enabled  to  exercise  unity  of  function. 

But,  on  the  whole,  it  is  more  probable,  that  the  power  of 
forming  a  single  idea  of  an  object  from  a  double  impression 
conveyed  by  it  to  the  eye  is  the  result  of  a  mental  act.  This 
view  is  supported  by  the  same  facts  as  those  employed  by 
Professor  Wheatstone  to  show  that  this  power  is  subservient  to 
the  purpose  of  obtaining  a  right  perception  of  bodies  raised  in 


FIG.  195. 


relief.  When  an  object  is  placed  so  near  the  eyes  that  to  view 
it  the  optic  axes  must  converge,  a  different  perspective  pro- 
jection of  it  is  seen  by  each  eye,  these  perspectives  being  more 
dissimilar  as  the  convergence  of  the  optic  axes  becomes  greater. 
Thus,  if  any  figure  of  three  dimensions,  an  outline  cube,  for 
example,  be  held  at  a  moderate  distance  before  the  eyes,  and 
viewed  with  each  eye  successively,  while  the  head  is  kept  per- 
fectly steady,  A  (Fig.  195)  will  be  the  picture  presented  to  the 
right  eye,  and  B  that  seen  by  the  left  eye.  Mr.  Wheatstone 
has  shown  that  on  this  circumstance  depends  in  a  great  meas- 
ure our  conviction  of  the  solidity  of  an  object,  or  of  its  pro- 
jection hi  relief.  If  different  perspective  drawings  of  a  solid 
body,  one  representing  the  image  seen  by  the  right  eye,  the 
other  that  seen  by  the  left  (for  example,  the  drawing  of  a 
cube  A,  B,  Fig.  195),  be  presented  to  corresponding  parts  of 
the  two  retinae,  as  may  be  readily  done  by  means  of  the  stereo- 
scope, an  instrument  invented  by  Professor  Wheatstone  for 
the  purpose,  the  mind  will  perceive  not  merely  a  single  rep- 
resentation of  the  object,  but  a  body  projecting  in  relief, 
the  exact  counterpart  of  that  from  which  the  drawings  were 
made. 


THE    SENSE    OF    HEARING. 


527 


FIG.  196. 


SENSE   OF    HEARING. 

Anatomy  of  the  Organ  of  Hearing. 

For  descriptive  purposes,  the  ear,  or  organ  of  hearing,  is 
divided  into  three  parts,  the  external,  the  middle,  and  the  in- 
ternal ear.  The  two  first  are  only  ac- 
cessory to  the  third  or  internal  ear, 
which  contains  the  essential  parts  of  an 
organ  of  hearing.  The  accompanying 
figure  shows  very  well  the  relation  of 
these  divisions — one  to  the  other  (Fig. 
196). 

The  external  ear  consists  of  the  pinna 
or  auricle,  and  the  external  auditory 
canal  or  meatm.  The  principal  parts 
of  the  pinna  are  two  prominent  rims 
inclosed  one  within  the  other  (helix  and 
antihelix},  and  inclosing  a  central  hol- 
low named  the  concha ;  in  front  of  the 
concha,  a  prominence  directed  back- 
wards, the  tragus,  and  opposite  to  this, 
one  directed  forwards,  the  antitragus. 
From  the  concha,  the  auditory  canal, 
with  a  slight  arch  directed  upwards, 
passes  inwards  and  a  little  forwards  to 
the  membrani  tympani,  to  which  it  thus 
serves  to  convey  the  vibrating  air.  Its 
outer  part  consists  of  fibro-cartilage 
continued  from  the  concha ;  its  inner  part  of  bone.  Both 
are  lined  by  skin  continuous  with  that  of  the  pinna,  and  ex- 
tending over  the  outer  part  of  the  membrana  tympani.  Towards 
the  outer  part  of  the  canal  are  fine  hairs  and  sebaceous  glands, 
while  deeper  in  the  canal  are  small  glands,  resembling  the 
sweat-glands  in  structure,  which  secrete  a  peculiar  yellow  sub- 
stance called  cerumen,  or  ear-wax. 

The  middle  ear,  or  tympanum  (b,  Fig.  197)  is  separated  by 
the  membrana  tympani  from  the  external  auditory  canal.  It 
is  a  cavity  in  the  temporal  bone,  opening  through  its  anterior 
and  inner  wall  into  the  Eustachian  tube,  a  cylindriform 
flattened  canal,  dilated  at  both  ends,  composed  partly  of  bone 
and  partly  of  cartilage,  lined  with  mucous  membrane,  and 
forming  a  communication  between  the  tympanum  and  the 
pharynx.  It  opens  into  the  cavity  of  the  pharynx  just  behind 


Outer  surface  of  the  pin- 
na of  the  right  auricle.  %. 
— 1,  helix;  2,  fossa  of  the 
helix  ;  3,  antihelix ;  4,  fossa 
of  the  antihelix;  5,  anti- 
tragus; 6,  tragus;  7,  con- 
cha ;  8,  lobule. 


528  THE    SENSE    OF    HEARING. 

the  posterior  aperture  of  the  nostrils.  The  cavity  of  the  tym- 
panum communicates  posteriorly  with  air-cavities,  the  mastoid 
cells  in  the  mastoid  process  of  the  temporal  bone ;  but  its  only 
opening  to  the  external  air  is  through  the  Eustachian  tube 
(c,  Fig.  197).  The  walls  of  the  tympanum  are  osseous,  except 
where  apertures  in  them  are  closed  with  membrane,  as  at  the 

FIG.  197. 


General  view  of  the  external,  middle,  and  internal  ear,  as  seen  in  a  prepared  sec- 
tion through  a,  the  auditory  canal,  b.  The  typanura  or  middle  ear.  c.  Eustachian 
tube,  leading  to  the  pharynx,  d.  Cochlea;  and  e.  Semicircular  canals  and  vestibule, 
seen  on  their  exterior,  as  brought  into  view  by  dissecting  away  the  surrounding 
petrous  bone.  The  styloid  process  projects  below,  and  the  inner  surface  of  the 
carotid  canal  is  seen  above  the  Eustachian  tubes  (from  Scarpa). 


fenestra  rotunda,  and  fenestra  ovalis,  and  at  the  outer  part 
where  the  bone  is  replaced  by  the  membrana  tympani.  The 
cavity  of  the  tympanum  is  lined  with  mucous  membrane,  the 
epithelium  of  which  is  ciliated  and  continuous  with  that  of  the 
pharynx.  It  contains  a  chain  of  small  bones  (ossicula  auditus), 
which  extends  from  the  membrana  tympani  to  the  fenestra 
ovalis. 

The  membrana  tympani  is  placed  in  a  slanting  direction  at 
the  bottom  of  the  external  auditory  canal,  its  plane  being  at 
an  angle  of  about  45°  with  the  lower  wall  of  the  canal.  It  is 


THE    LABYRINTH.  529 

formed  chiefly  of  a  tough  and  tense  fibrous  membrane,  the 
edges  of  which  are  set  in  a  bony  groove ;  its  outer  surface  is 
covered  with  a  continuation  of  the  cutaneous  lining  of  the 
auditory  canal,  its  inner  surface  with  part  of  the  ciliated  mucous 
membrane  of  the  tympanum. 

The  small  bones  or  ossicles  of  the  ear  are  three,  named 
malleus,  incus,  and  stapes.  The  malleus,  or  hammer-bone,  is 
attached  by  a  long  slightly-curved  process,  called  its  handle, 
to  the  membrani  tympani ;  the  line  of  attachment  being  verti- 
cal, including  the  whole  length  of  the  handle,  and  extending 
from  the  upper  border  to  the  centre  of  the  membrane.  The 
head  of  the  malleus  is  irregularly  rounded ;  its  neck,  or  the 
line  of  boundary  between  it  and  the  handle,  supports  two  pro- 
cesses ;  a  short  conical  one,  which  receives  the  insertion,  of  the 
tensor  tympani,  and  a  slender  one,  processus  gracilis,  which  ex- 
tends forwards,  and  to  which  the  laxator  tympani  muscle  is  at- 
tached. The  incus,  or  anvil-bone,  shaped  like  a  bicuspid  molar 
tooth,  is  articulated  by  its  broader  part,  corresponding  with 
the  surface  of  the  crown  of  a  tooth,  to  the  malleus.  Of  its  two 
fang-like  processes,  one,  directed  backwards,  has  a  free  end, 
the  other,  curved  downwards  and  more  pointed,  articulates  by 
means  of  a  roundish  tubercle,  formerly  called  os  orbiculare, 
with  the  stapes,  a  little  bone  shaped  exactly  like  a  stirrup,  of 
which  the  base  or  bar  fits  into  the  fenestra  ovalis.  To  the 
neck  of  the  stapes,  a  short  process,  corresponding  with  the  loop 
of  the  stirrup,  is  attached  the  stapedius  muscle. 

The  bones  of  the  ear  are  covered  with  mucous  membrane 
reflected  over  them  from  the  wall  of  the  tympanum;  and  are 
movable  both  altogether  and  one  upon  the  other.  The  malleus 
moves  and  vibrates  with  every  movement  and  vibration  of 
the  membrana  tympani,  and  its  movements  are  communicated 
through  the  incus  to  the  stapes,  and  through  it  to  the  mem- 
brane closing  the  fenestra  ovalis.  The  malleus,  also,  is  mova- 
ble in  its  articulation  with  the  incus ;  and  the  membrana 
tympani  moving  with  it  is  altered  in  its  degree  of  tension  by 
the  laxator  and  tensor  tympani  muscles.  The  stapes  is  mov- 
able on  the  process  of  the  incus,  when  the  stapedius  muscle 
acting  draws  it  backwards. 

The  proper  organ  of  hearing  is  formed  by  the  distribution 
of  the  auditory  nerve  within  the  internal  ear,  or  labyrinth  of 
the  ear,  a  set* of  cavities  within  the  petrous  portion  of  the 
temporal  bone.  The  bone  which  forms  the  walls  of  these 
cavities  is  denser  than  that  around  it,  and  forms  the  osseous 
labyrinth ;  the  membrane  within  the  cavities  forms  the  mem- 
branous labyrinth.  The  membranous  labyrinth  contains  a 


530  THE     SENSE    OF     HEARING. 

fluid  called  endolymph ;  while  outside  it,  between  it  and  the 
osseous,  labyrinth,  is  a  fluid  called  perilymph  (see  p.  533). 

The  osseous  labyrinth  consists  of  three  principal  parts, 
namely,  the  vestibule,  the  cochlea,  and  the  semicircular  canals. 
The  vestibule  is  the  middle  cavity  of  the  labyrinth,  and  the 
central  organ  of  the  whole  auditory  apparatus.  It  presents, 
in  its  inner  wall,  several  openings  for  the  entrance  of  the 
divisions  of  the  auditory  nerve;  in  its  outer  wall,  the  fenestra 
ovalis  (5,  Fig.  198),  an  opening  filled  by  the  base  of  the  stapes, 

FIG.  198. 


FIG.  198a. 


FIG.  198.— A  view  of  the  labyrinth  of  the  left  ear  of  a  foetus  of  8  months,  as  seen 
from  above.  Magnified  4  diameters.  1,2, 3.  The  cochlea.  1, 1.  Its  first  turn.  2,  2.  Its 
second  turn.  3,  3.  Its  third  or  half  turn,  and  apex  or  cupola.  4.  The  fenestra  ro- 
tunda. 5.  The  fenestra  ovalis.  6.  The  groove  around  it.  7,  7.  The  vestibule.  8,  9,  10. 
The  posterior  semicircular  canal,  with  its  ampulla  at  8.  11,  11.  The  superior  semi- 
circular canal.  12.  The  external  semicircular  canal. — (S.  &  H.) 

FIG.  198a.— An  outline,  of  the  natural  size,  of  figure  198. 

one  of  the  small  bones  of  the  ear ;  in  its  posterior  and  superior 
walls,  five  openings  by  which  the  semicircular  canals  communi- 
cate with  it :  in  its  anterior  wall,  an  opening  leading  into  the 
cochlea.  The  hinder  part  of  the  inner  wall  of  the  vestibule 
also  presents  an  opening,  the  orifice  of  the  aquceductus  vestibuli, 
a  canal  leading  to  the  posterior  margin  of  the  petrous  bone, 
with  uncertain  contents  and  unknown  purpose. 


THE     LABYRINTH.  531 

The  semicircular  canals  (Figs.  198,  199)  are  three  arched 
cylindriform  bony  canals,  set  in  the  substance  of  the  petrous 
bone.  They  all  open  at  both  ends  into  the  vestibule  (two  of 
them  first  coalescing).  The  ends  of  each  are  dilated  just  be- 

FlG. 199. 


Interior  of  the  osseous  labyrinth.  V.  Vestibule,  av.  Aqueduct  of  the  vestibule, 
o.  Fovea  hemielliptica.  r.  Fovea  hemispherica.  S.  Semicircular  canals.  *.  Su- 
perior, p.  Posterior,  i.  Inferior,  a,  a,  a.  The  ampullar  extremity  of  each.  C. 
Cochlea,  ac.  Aqueduct  of  the  cochlea,  sv.  Osseous  zone  of  the  lamina  spiralis, 
above  which  is  the  scala  vestibuli,  communicating  with  the  vestibule,  st.  Scala 
tympani  below  the  spiral  lamina.  From  Scemmerring. 

fore  opening  into  the  vestibule ;  and  one  end  of  each  being 
more  dilated  than  the  other  is  called  an  ampulla.  Two  of  the 
canals  form  nearly  vertical  arches ;  of  these  the  superior  is  also 
anterior;  the  posterior  is  inferior;  the  third  canal  is  horizontal, 
and  lower  and  shorter  than  the  others. 

The  cochlea  (1,  2,  3,  Fig.  198,  and  Fig.  200),  a  small  organ, 
shaped  like  a  common  snail  shell,  is  seated  in  front  of  the  ves- 
tibule, its  base  resting  on  the  bottom  of  the  internal  meatus, 
where  some  apertures  transmit  to  it  the  cochlear  filaments  of 
the  auditory  nerve.  In  its  axis,  the  cochlea  is  traversed  by 
a  conical  column,  the  modiolus,  around  which  a  spiral  canal 
winds  with  about  two  turns  and  a  half  from  the  base  to  the 
apex.  At  the  apex  of  the  cochlea  the  canal  is  closed ;  at  the 
base  it  presents  three  openings,  of  which  one,  already  men- 


532  THE    SENSE     OF     HEARING. 

tioued,  communicates  with  the  vestibule  ;  another,  called  fenes- 
tra  rotunda,  is  separated  by  a  membrane  from  the  cavity  of 
the  tympanum ;  the  third  is  the  orifice  of  the  aquceductus 
cochleae,  a  canal  leading  to  the  jugular  fossa  of  the  petrous 

bone,  and  corresponding,  at 

FlG-  20°-  least  in  obscurity   of  pur- 

pose and  origin,  to  the 
aquseductus  vestibuli.  The 
spiral  canal  is  divided  into 
two  passages  or  scalse  by  a 
partition  of  bone  and  mem- 
brane, the  lamina  spiralis. 
The  osseous  part  or  zone  of 
this  lamina  is  connected 

View  of  the  osseous  cochlea  divided  through  w[fa      t^e      modiolus;     the 

the  middle   (from  Arnold).    5.— 1,    central  mpmhranrms    nart     with     a 

canal  of   the   modiolus;   2,  lamina   spiralis  r  '    Part'    W™.    8 

ossea ;  3,  scala  tympani ;  4,  scala  vestibuli ;  5,  mUSCU  Jar     zone,     according 

porous  substance  of  the  modiolus  near  one  of  to       Todd     and      Bowman, 

the  sections  of  the  canalis  spiralis  modioli.  forming    its    OUter    margin, 

is  attached  to  the  outer 

wall  of  the  canal.  Commencing  at  the  base  of  the  cochlea, 
between  its  vestibular  and  tympanic  openings,  they  form  a 
partition  between  these  apertures  ;  the  two  scalse  are,  therefore, 
in  correspondence  with  this  arrangement,  named  scala  ves- 
tibuli and  scala  tympani.  At  the  apex  of  the  cochlea,  the 
lamina  spiralis  ends  in  a  small  hamulus,  the  inner  and  concave 
part  of  which,  being  detached  from  the  summit  of  the  modio- 
lus, leaves  a  small  aperture  named  helicotrema,  by  which  the 
two  scalse,  separated  in  all  the  rest  of  their  length,  communi- 
cate. 

Besides  the  scala  vestibuli  and  scala  tympani,  there  is  a  third 
space  between  them,  in  the  substance  of  the  lamina  spiralis, 
called  the  scala  media,  or  canalis  membranacea,  and  in  this  are 
some  peculiar  club-shaped  little  bodies  called  the  rods  of  Corti, 
set  up  on  end,  with  their  big  extremities  upwards,  and  leaning 
against  each  other  at  the  top — a  section,  therefore  having  the 
appearance  of  the  gable-end  of  a  house.  On  their  outer  part 
are  numerous  cells  of  various  shapes.  The  regularity  with 
which  the  little  rods  of  Corti  are  arranged  has  caused  them  to 
be  compared  to  rows  of  keys  in  a  piano. 

In  close  relation  with  these  rods  and  the  cells  outside  them, 
and  probably  projecting  also  by  free  ends  into  the  little  tri- 
angular canal  containing  fluid  which  is  between  the  rods,  are 
filaments  of  the  auditory  nerve. 

The  membranous  labyrinth  corresponds  generally  with  the 
form  of  the  osseous  labyrinth,  so  far  as  regards  the  vestibule 


THE    LABYRINTH.  533 

and  semicircular  canals,  but  is  separated  from  the  walls  of 
these  parts  by  fluid,  except  where  the  nerves  enter  into  con- 
nection within  it.  In  the  cochlea,  the  membranous  labyrinth 
completes  the  septum  between  the  two  scalce,  and  incloses  a 
separate  spiral  canal,  the  canalis  membranacea.  As  already 
mentioned,  the  membranous  labyrinth  contains  a  fluid  called 
endolyrnph ;  and  between  its  outer  surface  and  the  inner  sur- 
face of  the  walls  of  the  vestibule  and  semicircular  canals  is 
another  collection  of  similar  fluid  called  perilymph:  so  that 
all  the  sonorous  vibrations  impressing  the  auditory  nerves  on 
these  parts  of  the  internal  ear  are  conducted  through  fluid  to 
a  membrane  suspended  in  and  containing  fluid.  The  fluid  in 
the  scales  of  the  cochlea  is  continuous  with  the  perilymph  in  the 
vestibule  and  semicircular  canals,  and  there  is  no  fluid  exter- 
nal to  its  lining  membrane. 

The  vestibular  portion  of  the  membranous  labyrinth  com- 
prises two,  probably  communicating  cavities,  of  which  the 
larger  and  upper  is  named  the  utriculus ;  the  lower,  the  saccu- 
lus.  Into  the  former  open  the  orifices  of  the  membranous 
semicircular  canals ;  into  the  latter  the  canalis  membranacea 
of  the  cochlea.  The  membranous  labyrinth  of  all  these  parts 
is  laminated,  transparent,  very  vascular,  and  covered  on  the 
inner  surface  with  nucleated  cells,  of  which  those  that  line  the 
ampullae  are  prolonged  into  stiff  hair-like  processes;  the  same 
appearance,  but  to  a  much  less  degree,  being  visible  in  the 
utricle  and  saccule.  In  the  cavities  of  the  utriculus  and  saccu- 
lus  are  small  masses  of  calcareous  particles,  otoconia  or  otolithes; 
and  the  same,  although  in  more  minute  quantities,  are  to  be 
found  in  the  interior  of  other  parts  of  the  membranous  laby- 
rinth. 

The  auditory  nerve,  for  the  appropriate  exposure  of  whose 
filaments  to  sonorous  vibrations  all  the  organs  now  described 
are  provided,  is  characterized  as  a  nerve  of  special  sense  by  its 
softness  (whence  it  derived  its  name  of  portio  mollis  of  the 
seventh  pair),  and  by  the  fineness  of  its  component  fibres.  It 
enters  the  labyrinth  of  the  ear  in  two  divisions ;  one  for  the 
vestibule  and  semicircular  canals,  and  the  other  for  the  coch- 
lea. The  branches  for  the  vestibule  spread  out  and  radiate 
on  the  inner  surface  of  the  membranous  labyrinth  :  their  exact 
determination  is  unknown.  Those  for  the  semicircular  canals 
pass  into  the  ampullae,  and  form,  within  each  of  them,  a  forked 
projection  which  corresponds  with  a  septum  in  the  interior  of 
the  ampulla.  The  branches  for  the  cochlea  enter  it  through 
orifices  at  the  base  of  the  modiolus,  which  they  ascend,  and 
thence  successively  pass  into  canals  in  the  osseous  part  of  the 
lamina  spiralis.  In  the  canals  of  this  osseous  part  or  zone, 

45 


534  THE    SENSE    OF    HEARING. 

the  nerves  are  arranged  in  a  plexus,  containing  ganglion  cells. 
Their  ultimate  termination  is  not  known  with  certainty  ;  but 
some  of  them,  without  doubt,  end  in  the  organ  of  Corti,  prob- 
ably in  cells. 

Physiology  of  Hearing. 

The  acoustic  portion  of  the  physiology  of  hearing  is  thus  il- 
lustrated by  Miiller:  chiefly  in  applications  of  the  results  of 
his  experiments  on  the  conduction  of  sonorous  vibrations 
through  various  combinations  of  air,  water,  and  solid  sub- 
stances, especially  membrane. 

All  the  acoustic  contrivances  of  the  organ  of  hearing  are 
means  for  conducting  the  sound,  just  as  the  optical  apparatus 
of  the  eye  are  media  for  conducting  the  light.  Since  all  mat- 
ter is  capable  of  propagating  sonorous  vibrations,  the  simplest 
conditions  must  be  sufficient  for  mere  hearing ;  for  all  sub- 
stances surrounding  the  auditory  nerve  would  communicate 
sound  to  it.  In  the  eye  a  certain  construction  was  required 
for  directing  the  rays  or  undulations  of  light  in  such  a  man- 
ner that  they  should  fall  upon  the  optic  nerve  with  the  same 
relative  disposition  as  that  with  which  they  issued  from  the 
object.  In  the  sense  of  hearing  this  is  not  requisite.  Sonorous 
vibrations,  having  the  most  various  direction  and  the  most 
unequal  rate  of  succession,  are  transmitted  by  all  media  with- 
out modification,  however  manifold  their  decussations ;  and, 
wherever  these  vibrations  or  undulations  fall  upon  the  organ 
of  hearing  and  the  auditory  nerves,  they  must  cause  the  sensa- 
tion of  corresponding  sounds.  The  whole  development  of  the 
organ' of  hearing,  therefore,  can  have  for  its  object  merely  the 
rendering  more  perfect  the  propagation  of  the  sonorous  vibra- 
tions, and  their  multiplication  by  resonance ;  and,  in  fact,  all 
the  acoustic  apparatus  of  the  organ  may  be  shown  to  have 
reference  to  these  two  principals. 

Functions  of  the  External  Ear. 

The  external  auditory  passage  influences  the  propagation  of 
sound  to  the  tympanum  in  three  ways :  1,  by  causing  the 
sonorous  undulations,  entering  directly  from  the  atmosphere, 
to  be  transmitted  by  the  air  in  the  passage  immediately  to  the 
membrana  tympani,  and  thus  preventing  them  from  being 
dispersed ;  2,  by  the  walls  of  the  passage  conducting  the  so- 
norous undulations  imparted  to  the  external  ear  itself,  by  the 
shortest  path  to  the  attachment  of  the  membrana  tympani, 
and  so  to  this  membrane  ;  3,  by  the  resonance  of  the  column 
of  air  contained  within  the  passage. 


FUNCTIONS   OF   THE   EXTERNAL   EAR.         535 

As  a  conductor  of  undulations  of  air,  the  external  auditory 
passage  receives  the  direct  undulations  of  the  atmosphere,  of 
which  those  that  enter  in  the  direction  of  its  axis  produce  the 
strongest  impressions.  The  undulations  which  enter  the  pas- 
sage obliquely  are  reflected  by  its  parietes,  and  thus  by  reflec- 
tion reach  the  membrana  tympani.  By  reflection,  also,  the 
external  meatus  receives  the  undulations  which  impinge  upon 
the  concha  of  the  external  ear,  when  their  angle  of  reflection 
is  such  that  they  are  thrown  towards  the  tragus.  Other  sonor- 
ous undulations  again,  which  could  not  enter  the  meatus  from 
the  external  air  either  directly  or  by  reflection,  may  still  be 
brought  into  it  by  inflection ;  undulations,  for  instance,  whose 
direction  is  that  of  the  long  axis  of  the  head,  and  which  pass 
over  the  surface  of  the  ear,  must,  in  accordance  with  the  laws 
of  inflection,  be  bent  into  the  external  meatus  by  its  margins. 
But  the  action  of  those  undulations  which  enter  the  meatus 
directly  are  most  intense ;  and  hence  we  are  enabled  to  judge 
of  the  point  whence  sound  comes,  by  turning  one  ear  in  differ- 
ent directions,  till  it  is  directed  to  the  point  whence  the  vibra- 
tions may  pass  directly  into  the  meatus,  and  produce  the  strong- 
est impressions. 

The  walls  of  the  meatus  are  also  solid  conductors  of  sound ; 
for  those  vibrations  which  are  communicated  to  the  cartilage 
of  the  external  ear,  and  not  reflected  from  it,  are  propagated 
by  the  shortest  path  through  the  parietes  of  the  passage  to  the 
membrana  tympani.  Hence,  both  ears,  being  close  stopped, 
the  sound  of  a  pipe  is  heard  more  distinctly  when  its  lower 
extremity,  covered  with  a  membrane,  is  applied  to  the  carti- 
lage of  the  external  ear  itself,  than  when  it  is  placed  in  con- 
tact with  the  surface  of  the  head. 

Lastly,  the  external  auditory  passage  is  important,  inasmuch 
as  the  air  which  it  contains,  like  all  insulated  masses  of  air, 
increases  the  intensity  of  sounds  by  resonance.  To  convince 
ourselves  of  this,  we  need  only  lengthen  the  passage  by  affix- 
ing to  it  another  tube :  every  sound  that  is  heard,  even  the 
sound  of  our  own  voice,  is  then  much  increased  in  intensity. 

The  action  of  the  cartilage  of  the  external  ear  upon  sonor- 
ous vibrations  is  partly  to  reflect  them,  and  partly  to  condense 
and  conduct  them  to  the  parietes  of  the  external  passage. 
With  respect  to  its  reflecting  action,  the  concha  is  the  most 
important  part,  since  it  directs  the  reflected  undulations  to- 
wards the  tragus,  whence  they  are  reflected  into  the  auditory 
passage.  The  other  inequalities  of  the  external  ear  do  not 
promote  hearing  by  reflection ;  and,  if  the  conducting  power 
of  the  cartilage  of  the  ear  were  left  out  of  consideration,  they 
might  be  regarded  as  destined  for  no  particular  use ;  but  re- 


536  THE    SENSE    OF    HEARING. 

ceiving  the  impulses  of  the  air,  the  cartilage  of  the  external  ear, 
while  it  reflects  a  part  of  them,  propagates  within  itself  and 
condenses  the  rest,  as  all  other  solid  and  elastic  bodies  would 
do.  Thus,  the  sonorous  vibrations  which  it  receives  by  an  ex- 
tended surface,  are  conducted  by  it  to  its  place  of  attachment. 
In  consequence  of  the  connection  of  the  parietes  of  the  audi- 
tory passage  with  the  solid  parts  of  the  whole  head,  some  dis- 
persion of  the  undulations  will  result ;  but  the  points  of  at- 
tachment of  the  membrana  tympani  will  receive  them  by  the 
shortest  path,  and  will  as  certainly  communicate  them  to  that 
membrane,  as  the  solid  sides  of  a  drum  communicate  sonorous 
undulations  to  the  parchment  head,  or  the  bridge  of  a  musical 
string,  its  vibrations  to  the  string. 

Regarding  the  cartilage  of  the  external  ear,  therefore,  as  a 
conductor  of  sonorous  vibrations,  all  its  inequalities,  elevations, 
and  depressions,  which  are  useless  with  regard  to  reflection, 
become  of  evident  importance ;  for  those  elevations  and  de- 
pressions upon  which  the  undulations  fall  perpendicularly,  will 
be  affected  by  them  in  the  most  intense  degree  ;  and,  in  conse- 
quence of  the  various  form  and  position  of  these  inequalities, 
sonorous  undulations,  in  whatever  direction  they  may  come, 
must  fall  perpendicularly  upon  the  tangent  of  some  one  of 
them.  This  affords  an  explanation  of  the  extraordinary  form 
given  to  this  part. 

Functions  of  the  Middle  Ear :  the  Tympanum,  Ossicula,  and 
Fenestrce. 

In  animals  living  in  the  atmosphere,  the  sonorous  vibrations 
are  conveyed  to  the  auditory  nerve  by  three  different  media 
in  succession ;  namely,  the  air,  the  solid  parts  of  the  body  of 
the  animal  and  of  the  auditory  apparatus,  and  the  fluid  of  the 
labyrinth. 

Sonorous  vibrations  are  imparted  too  imperfectly  from  air 
to  solid  bodies,  for  the  propagation  of  sound  to  the  internal 
ear  to  be  adequately  effected  by  that  means  alone ;  yet  already 
an  instance  of  its  being  thus  propagated  has  been  mentioned. 

In  passing  from  air  directly  into  water,  sonorous  vibrations 
suffer  also  a  considerable  diminution  of  their  strength  ;  but  if 
a  tense  membrane  exists  between  the  air  and  the  water,  the 
sonorous  vibrations  are  communicated  from  the  former  to  the 
latter  medium  with  very  great  intensity.  This  fact,  of  which 
Mu'ller  gives  experimental  proof,  furnishes  at  once  an  expla- 
nation of  the  use  of  the  fenestra  rotunda,  and  of  the  membrane 
closing  it.  They  are  the  means  of  communicating,  in  full  in- 
tensity, the  vibrations  of  the  air  in  the  tympanum  to  the  fluid 


FUNCTIONS    OF    THE    MIDDLE    EAR.  537 

of  the  labyrinth.  This  peculiar  property  of  membranes  is  the 
result,  not  of  their  tenuity  alone,  but  of  the  elasticity  and  ca- 
pability of  displacement  of  their  particles ;  and  it  is  not  im- 
paired when,  like  the  membrane  of  the  fenestra  rotunda,  they 
are  not  impregnated  with  moisture. 

Sonorous  vibrations  are  also  communicated  without  any  per- 
ceptible loss  of  intensity  from  the  air  to  the  water,  when  to 
the  membrane  forming  the  medium  of  communication,  there 
is  attached  a  short,  solid  body,  which  occupies  the  greater  part 
of  its  surface,  and  is  alone  in  contact  with  the  water.  This 
fact  elucidates  the  action  of  the  fenestra  ovalis,  and  of  the 
plate  of  the  stapes  which  occupies  it,  and,  with  the  preceding 
fact,  shows  that  both  fenestrse — that  closed  by  membrane  only, 
and  that  with  which  the  movable  stapes  is  connected — trans- 
mit very  freely  the  sonorous  vibrations  from  the  air  to  the  fluid 
of  the  labyrinth. 

A  small,  solid  body,  fixed  in  an  opening  by  means  of  a 
border  of  membrane,  so  as  to  be  movable,  communicates  sonor- 
ous vibrations  from  air  on  the  one  side,  to  water,  or  the  fluid 
of  the  labyrinth,  on  the  other  side,  much  better  than  solid 
media  not  so  constructed.  But  the  propagation  of  sound  to 
the  fluid  is  rendered  much  more  perfect  if  the  solid  conductor 
thus  occupying  the  opening,  or  feiiestra  ovalis,  is  by  its  other 
end  fixed  to  the  middle  of  a  tense  membrane,  which  has  atmos- 
pheric air  on  both  sides. 

A  tense  membrane  is  a  much  better  conductor  of  the  vibra- 
tions of  air  than  any  other  solid  body  bounded  by  definite 
surfaces:  and  the  vibrations  are  also  communicated  very 
readily  by  tense  membranes  to  solid  bodies  in  contact  with 
them.  Thus,  then,  the  membrana  tympani  serves  for  the  trans- 
mission of  sound  from  the  air  to  the  chain  of  auditory  bones. 
Stretched  tightly  in  its  osseous  ring,  it  vibrates  with  the  air  in 
the  auditory  passage,  as  any  thin  tense  membrane  will  when 
the  air  near  it  is  thrown  into  vibrations  by  the  sounding  of  a 
tuning-fork  or  a  musical  string.  And,  from  such  a  tense  vi- 
brating membrane,  the  vibrations  are  communicated  with  great 
intensity  to  solid  bodies  which  touch  it  at  any  point.  If,  for 
example,  one  end  of  a  flat  piece  of  wood  be  applied  to  the 
membrane  of  a  drum  while  the  other  end  is  held  in  the  hand, 
vibrations  are  felt  distinctly  when  the  vibrating  tuning-fork  is 
held  over  the  membrane  without  touching  it ;  but  the  wood 
alone,  isolated  from  the  membrane,  will  only  very  feebly  propa- 
gate the  vibrations  of  the  air  to  the  hand. 

The  ossicula  of  the  ear,  which  are  represented  in  this  experi- 
ment by  a  piece  of  wood,  are  the  better  conductors  of  the  so- 
norous vibrations  communicated  to  them,  on  account  of  being 


538  THE    SENSE    OF    HEARING. 

isolated  by  an  atmosphere  of  air,  and  not  continuous  with  the 
bones  of  the  cranium;  for  every  solid  body  thus  isolated  by  a 
different  medium  propagates  vibrations  with  more  intensity 
through  its  own  substance  than  it  communicates  them  to  the 
surrounding  medium,  which  thus  prevents  a  dispersion  of  the 
sound ;  just  as  the  vibrations  of  the  air  in  the  tubes  used  for 
conducting  the  voice  from  one  apartment  to  another  are  pre- 
vented from  being  dispersed  by  the  solid  walls  of  the  tube. 
The  vibrations  of  the  membraua  tympani  are  transmitted, 
therefore,  by  the  chain  of  ossicula  to  the  fenestra  ovalis  and 
fluid  of  the  labyrinth,  their  dispersion  in  the  tympanum  being 
prevented  by  the  difficulty  of  the  transition  of  vibrations  from 
solid  to  gaseous  bodies.  The  mernbrana  tympani  being  a 
tense,  solid  body,  bounded  by  free  surfaces,  the  sonorous  undu- 
lations will  be  partially  reflected  at  its  surfaces,  so  as  to  cause 
a  meeting  of  undulations  from  opposite  directions  within  it;  it 
will,  therefore,  by  resonance,  increase  the  intensity  of  the  vi- 
brations communicated  to  it,  and  the  undulations,  thus  ren- 
dered more  intense,  will  act,  in  their  turn,  upon  the  chain  of 
auditory  bones. 

The  necessity  of  the  presence  of  air  on  the  inner  side  of  the 
membrana  tympani,  in  order  to  enable  it  and  the  ossicula  au- 
ditus  to  fulfil  the  objects  just  described,  is  obvious.  Without 
this  provision,  neither  would  the  vibrations  of  the  membrane 
be  free,  nor  the  chain  of  bones  isolated,  so  as  to  propagate  the 
sonorous  undulations  with  concentration  of  their  intensity. 
But  while  the  oscillations  of  the  membrana  tympani  are  readily 
communicated  to  the  air  in  the  cavity  of  the  tympanum,  those 
of  the  solid  ossicula  will  not  be  conducted  away  by  the  air,  but 
will  be  propagated  to  the  labyrinth  without  being  dispersed  in 
the  tympanum.  Equally  necessary  is  the  communication  of 
the  air  in  the  tympanum  with  the  external  air,  through  the 
medium  of  the  Eustachian  tube,  for  the  maintenance  of  the 
equilibrium  of  pressure  and  temperature  between  them. 

The  propagation  of  sound  through  the  ossicula  of  the  tym- 
panum to  the  labyrinth  must  be  effected  either  by  oscillations 
of  the  bones,  or  by  a  kind  of  molecular  vibration  of  their  par- 
ticles, or,  most  probably,  by  both  these  kinds  of  motion.1 


1  Edouard  Weber  has  shown  that  the  existence  of  the  membrane 
over  the  fenestra  rotunda  will  permit  approximation  and  removal  of 
the  stapes  to  and  from  the  labyrinth.  When  by  the  stapes  the  mem- 
brane of  the  fenestra  ovalis  is  pressed  towards  the  labyrinth,  the  mem- 
brane of  the  fenestra  rotunda  may,  by  the  pressure  communicated 
through  the  fluid  of  the  labyrinth,  be  pressed  towards  the  cavity  of 
the  tympanum. 


FUNCTIONS    OF    THE    MIDDLE    EAR.  539 

The  long  process  of  the  malleus  receives  the  undulations  of 
the  membrana  tympani  (Fig.  201,  a,  a)  and  of 
the  air  in  a  direction  indicated  by  the  arrows,  FlG-  201- 

nearly  perpendicular  to  itself.  From  the 
long  process  of  the  malleus  they  are  propa- 
gated to  its  head  (6) ;  thence  into  the  incus 
(e),  the  long  process  of  which  is  parallel  with 
the  long  process  of  the  malleus.  From  the 
long  process  of  the  incus  the  undulations  are 
communicated  to  the  stapes  (d),  which  is 
united  to  the  incus  at  right  angles.  The 
several  changes  in  the  direction  of  the  chain 
of  bones  have,  however,  no  influence  on  that 
of  the  undulations,  which  remains  the  same 
as  it  was  in  the  meatus  externus  and  long 
process  of  the  malleus,  so  that  the  undula- 
tions are  communicated  by  the  stapes  to  the 
fenestra  ovalis  in  a  perpendicular  direction. 

Increasing  tension  of  the  membrana  tympani  diminishes  the 
facility  of  transition  of  sonorous  undulations  from  the  air  to  it. 
Mr.  Savart  observed  that  the  dry  membrana  tympani,  on  the 
approach  of  a  body  emitting  a  loud  sound,  rejected  particles 
of  sand  strewn  upon  it  more  strongly  when  lax  than  when  very 
tense ;  and  inferred,  therefore,  that  hearing  is  rendered  less 
acute  by  increasing  the  tension  of  the  membrana  tympani. 
Mu'ller  has  confirmed  this  by  experiments  with  small  mem- 
branes arranged  so  as  to  imitate  the  membrana  tympani ;  and 
it  may  be  confirmed  also  by  observations  on  one's  self.  For 
the  membrana  tympani  on  one's  own  person  may  be  rendered 
tense  at  will  in  two  ways,  namely,  by  a  strong  and  continued 
effort  of  expiration  or  of  inspiration  while  the  mouth  and  nos- 
trils are  closed.  In  the  first  case,  the  compressed  air  is  forced 
with  a  whizzing  sound  into  the  tympanum,  the  membrana  tym- 
pani is  made  tense,  and  immediately  hearing  becomes  indis- 
tinct. The  same  temporary  imperfection  of  hearing  is  pro- 
duced by  rendering  the  membrana  tympani  tense,  and  convex 
towards  the  interior,  by  the  effort  of  inspiration.  The  imper- 
fection of  hearing,  produced  by  the  last-mentioned  method, 
may  continue  for  a  time  even  after  the  mouth  is  opened,  in 
consequence  of  the  previous  effort  at  inspiration  having  in- 
duced collapse  of  the  walls  of  the  Eustachian  tube,  which  pre- 
vents the  restoration  of  equilibrium  of  pressure  between  the  air 
within  the  tympanum  and  that  without :  hence  we  have  the 
opportunity  of  observing  that  even  our  own  voice  is  heard  with 
less  intensity  when  the  tension  of  the  membrana  tympani  is 
great. 


540  THE    SENSE    OF    HEARING. 

If  the  pressure  of  the  external  air  or  atmosphere  be  very 
great,  while  on  account  of  collapse  of  the  walls  of  the  Eusta- 
chian  tube,  the  air  in  the  interior  of  the  tympanum  fails  to 
exert  an  equal  counter-pressure,  the  membrana  tympani  will 
of  course  be  forced  inwards,  and  imperfect  deafness  be  pro- 
duced. Thus  it  may  be  explained  why,  in  a  diving-bell,  voices 
sound  faintly.  In  all  cases,  the  effect  of  the  increased  tension 
of  the  membrana  tympani  is  not  to  render  both  grave  and 
acute  sounds  equally  fainter  than  before.  On  the  contrary,  as 
observed  by  Dr.  Wollaston,  the  increased  tension  of  the  mem- 
brana tympani,  produced  by  exhausting  the  cavity  of  the 
tympanum,  makes  one  deaf  to  grave  sounds  only. 

The  principal  office  of  the  Eustachian  tube,  in  Muller's 
opinion,  has  relation  to  the  prevention  of  these  effects  of  in- 
creased tension  of  the  membrana  tympani.  Its  existence  and 
openness  will  provide  for  the  maintenance  of  the  equilibrium 
between  the  air  within  the  tympanum  and  the  external  air,  so 
as  to  prevent  the  inordinate  tension  of  the  membrana  tympani 
which  would  be  produced  by  too  great  or  too  little  pressure  on 
either  side.  While  discharging  this  office,  however,  it  will 
serve  to  render  sounds  clearer,  as  (Henle  suggests)  the  aper- 
tures in  violins  do ;  to  supply  the  tympanum  with  air ;  and  to 
be  an  outlet  for  mucus :  and  the  ill  effects  of  its  obstruction 
may  be  referred  to  the  hindrance  of  all  these  its  offices,  as  well 
as  of  that  one  ascribed  to  it  as  its  principal  use. 

The  influence  of  the  tensor  tympani  muscle  in  modifying 
hearing  may  also  be  probably  explained  in  connection  with 
the  regulation  of  the  tension  of  the  membrana  tympani.  If, 
through  reflex  nervous  action,  it  can  be  excited  to  contraction 
by  a  very  loud  sound,  just  as  the  iris  and  orbicularis  palpe- 
brarum  muscle  are  by  a  very  intense  light,  then  it  is  manifest 
that  a  very  intense  sound  would,  through  the  action  of  this 
muscle,  induce  a  deafening  or  muffling  of  the  ears.  In  favor 
of  this  supposition  we  have  the  fact  that  a  loud  sound  excites, 
by  reflection,  nervous  action,  winking  of  the  eyelids,  and,  in 
persons  of  irritable  nervous  system,  a  sudden  contraction  of 
many  muscles. 

The  influence  of  the  stapedius  muscle  in  hearing  is  unknown. 
It  acts  upon  the  stapes  in  such  a  manner  as  to  make  it  rest 
obliquely  in  the  fenestra  ovalis,  depressing  that  side  of  it  on 
which  it  acts,  and  elevating  the  other  side  to  the  same  extent. 

When  the  fenestra  ovalis  and  fenestra  rotunda  exist  together 
with  a  tympanum,  the  sound  is  transmitted  to  the  fluid  of  the 
internal  ear  in  two  ways, — namely,  by  solid  bodies  and  by 
membrane ;  by  both  of  which  conducting  media  sonorous  vibra- 
tions are  communicated  to  water  with  considerable  intensity. 


FUNCTIONS    OF    THE    LABYRINTH.  541 

The  sound  being  conducted  to  the  labyrinth  by  two  paths,  will, 
of  course,  produce  so  much  the  stronger  impression  ;  for  undu- 
lations will  be  thus  excited  in  the  fluid  of  the  labyrinth  from 
two  different  though  contiguous  points ;  and  by  the  crossing  of 
these  undulations  stationary  waves  of  increased  intensity  will 
be  produced  in  the  fluid.  Miiller's  experiments  show  that  the 
same  vibrations  of  the  air  act  upon  the  fluid  of  the  labyrinth 
with  much  greater  intensity  through  the  medium  of  the  chain 
of  auditory  bones  and  the  fenestra  oval  is  than  through  the 
medium  of  the  air  of  the  tympanum  and  the  membrane  closing 
the  fenestra  rotunda :  but  the  cases  of  disease  in  which  the 
ossicula  have  been  lost  without  loss  of  hearing,  prove  that  sound 
may  also  be  well  conducted  through  the  air  of  the  tympanum 
and  the  membrane  of  the  fenestra  rotunda. 

Functions  of  the  Labyrinth. 

The  fluid  of  the  labyrinth  is  the  most  general  and  constant 
of  the  acoustic  provisions  of  the  labyrinth.  In  all  forms  of 
organs  of  hearing,  the  sonorous  vibrations  affect  the  auditory 
nerve  through  the  medium  of  liquid — the  most  convenient 
medium,  on  many  accounts,  for  such  a  purpose. 

The  function  usually  ascribed  to  the  semicircular  canals  is 
the  collecting  in  their  fluid  contents,  the  sonorous  undulations 
from  the  bones  of  the  cranium.  They  have  probably,  also,  in 
some  degree,  the  power  of  conducting  sounds  in  the  direction 
of  their  curved  cavities  more  easily  than  the  sounds  are  carried 
off  by  the  surrounding  hard  parts  in  the  original  direction  of 
the  undulations,  though  this  conducting  power  is  in  them  much 
less  perfect  than  in  tubes  containing  air. 

Admitting  that  they  have  these  powers,  the  increased  inten- 
sity of  the  sonorous  vibrations  thus  attained  will  be  of  advan- 
tage in  acting  on  the  auditory  nerve  where  it  is  expanded  in 
the  ampullae  of  the  canals,  and  in  the  utriculus.  Where  the 
membranous  canals  are  in  contact  with  the  solid  parietes  of 
the  tubes,  this  action  must  be  much  more  intense.  But  the 
membranous  semicircular  canals  must  have  a  function  inde- 
pendent of  the  surrounding  hard  parts ;  for  in  the  Petromyzon 
they  are  not  separately  inclosed  in  solid  substance,  but  lie  in 
one  common  cavity  with  the  utriculus. 

The  crystalline  pulverulent  masses  in  the  labyrinth  would  re- 
inforce the  sonorous  vibrations  by  their  resonance,  even  if  they 
did  not  actually  touch  the  membranes  upon  which  tjie  nerves 
are  expanded ;  but,  inasmuch  as  these  bodies  lie  in  contact 
with  the  membranous  parts  of  the  labyrinth,  and  the  vestibur 
lar  nerve-fibres  are  imbedded  in  them,  they  commupicate  to 

40 


542  THE    SENSE    OF    HEARING. 

these  membranes  and  the  nerves  vibratory  impulses  of  greater 
intensity  than  the  fluid  of  the  labyrinth  can  impart.  This  ap- 
pears to  be  the  office  of  the  otoconia.  Sonorous  undulations 
in  water  are  not  perceived  by  the  hand  itself  immersed  in  the 
water,  but  are  felt  distinctly  through  the  medium  of  a  rod  held 
in  the  hand.  The  fine  hair-like  prolongations  from  the  epi- 
thelial cells  of  the  ampullae  have,  probably,  the  same  function. 

The  cochlea  seems  to  be  constructed  for  the  spreading  out  of 
the  nerve  fibres  over  a  wide  extent  of  surface,  upon  a  solid 
lamina  which  communicates  with  the  solid  walls  of  the  laby- 
rinth and  cranium,  at  the  same  time  that  it  is  in  contact  with 
the  fluid  of  the  labyrinth,  and  which,  besides  exposing  the 
nerve-fibres  to  the  influence  of  sonorous  undulations  by  two 
media,  is  itself  insulated  by  fluid  on  either  side. 

The  connection  of  the  lamina  spiralis  with  the  solid  walls  of 
the  labyrinth,  adapts  the  cochlea  for  the  perception  of  the 
sonorous  undulations  propagated  by  the  solid  parts  of  the  head 
and  the  walls  of  the  labyrinth.  The  membranous  labyrinth 
of  the  vestibule  and  semicircular  canals  is  suspended  free  in 
the  perilymph,  and  is  destined  more  particularly  for  the  per- 
ception of  sounds  through  the  medium  of  that  fluid,  whether 
the  sonorous  undulations  be  imparted  to  the  fluid  through  the 
fenestrse,  or  by  the  intervention  of  the  cranial  bones,  as  when 
sounding  bodies  are  brought  into  communication  with  the  head 
or  teeth.  The  spiral  lamina  on  which  the  nervous  fibres  are 
expanded  in  the  cochlea,  is,  on  the  contrary,  continuous  with 
the  solid  walls  of  the  labyrinth,  and  receives  directly  from  them 
the  impulses  which  they  transmit.  This  is  an  important  advan- 
tage; for  the  impulses  imparted  by  solid  bodies,  have,  cceteris 
paribus,  a  greater  absolute  intensity  than  those  communicated 
by  water.  And,  even  when  a  sound  is  excited  in  the  water, 
the  sonorous  undulations  are  more  intense  in  the  water  near 
the  surface  of  the  vessel  containing  it,  than  in  other  parts  of 
the  water  equally  distant  from  the  point  of  origin  of  the  sound  : 
thus  we  may  conclude  that,  cceteris  paribus,  the  sonorous  undu- 
lations of  solid  bodies  act  with  greater  intensity  than  those  of 
water.  Hence  we  perceive  at  once  an  important  use  of  the 
cochlea. 

This  is  not,  however,  the  sole  office  of  the  cochlea  ;  the  spiral 
lamina,  as  well  as  the  membranous  labyrinth,  receives  sonor- 
ous impulses  through  the  medium  of  the  fluid  of  the  labyrinth 
from  the  cavity  of  the  vestibule  and  from  the  fenestra  rotunda. 
The  lamina  spiralis  is,  indeed,  much  better  calculated  to  render 
the  action  of  these  undulations  upon  the  auditory  nerve  effi- 
cient, than  the  membranous  labyrinth  is ;  for,  as  a  solid  body 
insulated  by  a  different  medium,  it  is  capable  of  resonance. 


SENSIBILITY   OF   THE    AUDITORY    NERVE.       543 

The  rods  of  Corti  are  probably  arranged  so  that  each  is  set 
to  vibrate  in  unison  with  a  particular  tone,  and  thus  strike  a 
particular  note,  the  sensation  of  which  is  carried  to  the  brain 
by  those  filaments  of  the  auditory  nerve  with  which  the  little 
vibrating  rod  is  connected. 

The  distinctive  function  therefore  of  these  minute  bodies  is, 
probably,  to  render  sensible  to  the  brain  the  various  musical 
notes  and  tones,  one  of  them  answering  to  one  tone,  and  one  to 
another ;  while  perhaps  the  other  parts  of  the  organ  of  hearing 
discriminate  between  the  intensities  of  different  sounds,  rather 
than  their  qualities. 

Sensibility  of  the  Auditory  Nerve. 

Most  frequently,  several  undulations  or  impulses  on  the 
auditory  nerve  concur  in  the  production  of  the  impressions  of 
sound. 

By  the  rapid  succession  of  several  impulses  at  unequal  inter- 
vals, a  noise  or  rattle  is  produced ;  from  a  rapid  succession  of 
several  impulses  at  equal  intervals,  a  musical  sound  results, 
the  height  or  acuteness  of  which  increases  with  the  number  of 
the  impulses  communicated  to  the  ear  within  a  given  time.  A 
sound  of  definite  musical  value  is  also  produced  when  each  one 
of  the  impulses,  succeeding  another  thus  at  regular  intervals, 
is  itself  compounded  of  several  undulations,  in  such  a  way  that, 
heard  alone,  it  would  give  the  impression  of  an  unmusical 
sound;  that  is  to  say,  by  a  sufficiently  rapid  succession  of 
short  unmusical  sounds  at  regular  intervals,  a  musical  sound 
is  generated. 

It  would  appear  that  two  impulses,  which  are  equivalent  to 
four  single  or  half  vibrations,  are  sufficient  to  produce  a  definite 
note,  audible  as  such  through  the  auditory  nerve.  The  note 
produced  by  the  shocks  of  the  teeth  of  a  revolving  wheel,  at 
regular  intervals  upon  a  solid  body,  is  still  heard  when  the 
teeth  of  the  wheel  are  removed  in  succession,  until  two  only 
are  left ;  the  sound  produced  by  the  impulse  of  these  two  teeth 
has  still  the  same  definite  value  in  the  scale  of  music. 

The  maximum  and  minimum  of  the  intervals  of  successive 
impulses  still  appreciable  through  the  auditory  nerve  as  de- 
terminate sounds,  have  been  determined  by  M.  Savart.  If 
their  intensity  is  sufficiently  great,  sounds  are  still  audible 
which  result  from  the  succession  of  48,000  half  vibrations,  or 
24,000  impulses  in  a  second ;  and  this,  probably,  is  not  the 
extreme  limit  in  acuteness  of  sounds  perceptible  by  the  ear. 
For  the  opposite  extreme,  he  has  succeeded  in  rendering  sounds 
audible  which  were  produced  by  only  fourteen  or  eighteen  half 


544  THE    SENSE    OF     HEARING. 

vibrations,  or  seven  or  eight  impulses  in  a  second ;  and  sounds 
still  deeper  might  probably  be  heard,  if  the  individual  im- 
pulses could  be  sufficiently  prolonged. 

By  removing  one  or  several  teeth  from  the  toothed  wheel 
before  mentioned,  M.  Savart  was  also  enabled  to  satisfy  himself 
of  the  fact,  that  in  the  case  of  the  auditory  nerve,  as  in  that 
of  the  optic  nerve,  the  sensation  continues  longer  than  the 
impression  which  causes  it ;  for  the  removal  of  a  tooth  from 
the  wheel  produced  no  interruption  of  the  sound.  The  gradual 
cessation  of  the  sensation  of  sound  renders  it  difficult,  how- 
ever, to  determine  its  exact  duration  beyond  that  of  the  im- 
pression of  the  sonorous  impulses. 

The  power  of  perceiving  the  direction  of  sounds  is  not  a 
faculty  of  the  sense  of  hearing  itself,  but  is  an  act  of  the  mind 
judging  on  experience  previously  acquired.  From  the  modifi- 
cations which  the  sensation  of  sound  undergoes  according  to 
the  direction  in  which  the  sound  reaches  us,  the  mind  infers 
the  position  of  the  sounding  body.  The  only  true  guide  for 
this  inference  is  the  more  intense  action  of  the  sound  upon  one 
than  upon  the  other  ear.  But  even  here  there  is  room  for 
much  deception,  by  the  influence  of  reflection  or  resonance, 
and  by  the  propagation  of  sound  from  a  distance,  without  loss 
of  intensity,  through  curved  conducting-tubes  filled  with  air. 
By  means  of  such  tubes,  or  of  solid  conductors,  which  convey 
the  sonorous  vibrations  from  their  source  to  a  distant  resonant 
body,  sounds  may  be  made  to  appear  to  originate  in  a  new 
situation. 

The  direction  of  sound  may  also  be  judged  of  by  means  of 
one  ear  only ;  the  position  of  the  ear  and  head  being  varied, 
so  that  the  sonorous  undulations  at  one  moment  fall  upon  the 
ear  in  a  perpendicular  direction,  at  another  moment  obliquely. 
But  when  neither  of  these  circumstances  can  guide  us  in  dis- 
tinguishing the  direction  of  sound,  as  when  it  falls  equally 
upon  both  ears,  its  source  being,  for  example,  either  directly 
in  front  or  behind  us,  it  becomes  impossible  to  determine 
whence  the  sound  comes. 

Ventriloquists  take  advantage  of  the  difficulty  with  which 
the  direction  of  sound  is  recognized,  and  also  the  influence  of 
the  imagination  over  our  judgment,  when  they  direct  their 
voice  in  a  certain  direction,  and  at  the  same  time  pretend 
themselves  to  hear  the  sounds  as  coming  from  thence. 

The  distance  of  the  source  of  sounds  is  not  recognized  by  the 
sense  itself,  but  is  inferred  from  their  intensity.  The  sound 
itself  is  always  seated  but  in  one  place,  namely,  in  our  ear ; 
but  it  is  interpreted  as  coming  from  an  exterior  soniferous 
body.  When  the  intensity  of  the  voice  is  modified  in  imita- 


DIRECTION    AND    DISTANCE    OF    SOUNDS.       545 

tion  of  the  effect  of  distance,  it  excites  the  idea  of  its  originat- 
ing at  a  distance;  and  this  is  also  taken  advantage  of  by  ven- 
triloquists. 

The  experiments  of  Savart,  already  referred  to,  prove  that 
the  effect  of  the  action  of  sonorous  undulations  upon  the  nerve 
of  hearing,  endures  somewhat  longer  than  the  period  during 
which  the  undulations  are  passing  through  the  ear.  If,  how- 
ever, the  impression  of  the  same  sound  be  very  long  continued, 
or  constantly  repeated  for  a  long  time,  then  the  sensation  pro- 
duced may  continue  for  a  very  long  time,  more  than  twelve  or 
twenty-four  hours  even,  after  the  original  cause  of  the  sound 
has  ceased.  This  must  have  been  experienced  by  every  one 
who  has  travelled  several  days  continuously ;  for  some  time 
after  the  journey,  the  rattling  noises  are  heard  when  the  ear 
is  not  acted  on  by  other  sounds. 

We  have  here  a  proof  that  the  perception  of  sound,  as 
sound,  is  not  essentially  connected  with  the  existence  of  undu- 
latory  pulses  ;  and  that  the  sensation  of  sound  is  a  state  of  the 
auditory  nerve,  which,  though  it  may  be  excited  by  a  succes- 
sion of  impulses,  may  also  be  produced  by  other  causes.  Even 
if  it  be  supposed  that  undulations  excited  by  the  impulse  are 
kept  up  in  the  auditory  nerve  for  a  certain  time,  they  must  be 
undulations  of  the  nervous  principle  itself,  which,  being  ex- 
cited, continue  until  the  equilibrium  is  restored. 

Corresponding  to  the  double  vision  of  the  same  object  with 
the  two  eyes,  is  the  double  hearing  with  the  two  ears ;  and 
analogous  to  the  double  vision  with  one  eye,  dependent  on 
unequal  refraction,  is  the  double  hearing  of  a  single  sound 
with  one  ear,  owing  to  the  sound  coming  to  the  ear  through 
media  of  unequal  conducting  power.  The  first  kind  of  double 
hearing  is  very  rare  ;  instances  of  it  are  recorded,  however,  by 
Sauvages  and  Itard.  The  second  kind,  which  depends  on  the 
unequal  conducting  power  of  two  media  through  which  the 
same  sound  is  transmitted  to  the  ear,  may  easily  be  experi- 
enced. If  a  small  bell  be  sounded  in  water,  while  the  ears 
are  closed  by  plugs,  and  a  solid  conductor  be  interposed  be- 
tween the  water  and  the  ear,  two  sounds  will  be  heard  differ- 
ing in  tensity  and  tone ;  one  being  conveyed  to  the  ear  through 
the  medium  of  the  atmosphere,  the  other  through  the  conduct- 
ing-rod. 

The  sense  of  vision  may  vary  in  its  degree  of  perfection  as 
regards  either  the  faculty  of  adjustment  to  different  distances, 
the  power  of  distinguishing  accurately  the  particles  of  the 
retina  affected,  sensibility  to  light  and  darkness,  or  the  per- 
ception of  the  different  shades  of  color.  In  the  sense  of  hear- 
ing, there  is  no  parallel  to  the  faculty  by  which  the  eye  is 


546  THE    SENSE    OF     HEARING. 

accommodated  to  distance,  nor  to  the  perception  of  the  particu- 
lar part  of  the  nerve  affected  ;  but  just  as  one  person  sees  dis- 
tinctly only  in  a  bright  light,  and  another  only  in  a  moderate 
light,  so  in  different  individuals  the  sense  of  hearing  is  more 
perfect  for  sounds  of  different  pitch  ;  and  just  as  a  person 
whose  vision  for  the  forms  of  objects,  &c.,  is  acute,  neverthe- 
less distinguishes  colors  with  difficulty,  and  has  no  perception 
of  the  harmony  and  disharmony  of  colors,  so  one,  whose  hear- 
ing is  good  as  far  as  regards  the  sensibility  to  feeble  sounds,  is 
sometimes  deficient  in  the  power  of  recognizing  the  musical 
relation  of  sounds,  and  in  the  sense  of  harmony  and  discord  ; 
while  another  individual,  whose  hearing  is  in  other  respects 
imperfect,  has  these  endowments.  The  causes  of  these  differ- 
ences are  unknown. 

Subjective  sounds  are  the  result  of  a  state  of  irritaton  or 
excitement  of  the  auditory  nerve  produced  by  other  causes 
than  sonorous  impulses.  A  state  of  excitement  of  this  nerve, 
however  induced,  gives  rise  to  the  sensation  of  sound.  Hence 
the  ringing  and  buzzing  in  the  ears  heard  by  persons  of  irrita- 
ble and  exhausted  nervous  system,  and  by  patients  with  cerebral 
disease,  or  disease  of  the  auditory  nerve  itself;  hence  also  the 
noise  in  the  ears  heard  for  some  time  after  a  long  journey  in  a 
rattling  noisy  vehicle.  Hitter  found  that  electricity  also  excites 
a  sound  in  the  ears.  From  the  above  truly  subjective  sound 
we  must  distinguish  those  dependent,  not  on  a  state  of  the  audi- 
tory nerve  itself  merely,  but  on  sonorous  vibrations  excited  in 
the  auditory  apparatus.  Such  are  the  buzzing  sounds  atten- 
dant on  vascular  congestion  of  the  head  and  ear,  or  on  aneu- 
rismal  dilatation  of  the  vessels.  Frequently  even  the  simple 
pulsatory  circulation  of  the  blood  in  the  ear  is  heard.  To  the 
sounds  of  this  class  belong  also  the  snapping  sound  in  the  ear 
produced  by  a  voluntary  effort,  and  the  buzz  or  hum  heard 
during  the  contraction  of  the  palatine  muscles  in  the  act  of 
yawning ;  during  the  forcing  of  air  into  the  tympanum,  so  as 
to  make  tense  the  membrana  tympani ;  and  in  the  act  of  blow- 
ing the  nose,  as  well  as  during  the  forcible  depression  of  the 
lower  jaw. 

Irritation  or  excitement  of  the  auditory  nerve  is  capable  of 
giving  rise  to  movements  in  the  body,  and  to  sensations  in 
other  organs  of  sense.  In  both  cases  it  is  probable  that  the 
laws  of  reflex  action,  through  the  medium  of  the  brain,  come 
into  play.  An  intense  and  sudden  noise  excites,  in  every 
person,  closure  of  the  eyelids,  and,  in  nervous  individuals,  a 
start  of  the  whole  body  or  an  unpleasant  sensation,  like  that 
produced  by  an  electric  shock,  throughout  the  body,  and 
sometimes  a  particular  feeling  in  the  external  ear.  Various 


THE    SENSE    OF    TASTE.  547 

sounds  cause  in  many  people  a  disagreeable  feeling  in  the 
teeth,  or  a  sensation  of  cold  trickling  through  the  body,  and, 
in  some  people,  intense  sounds  are  said  to  make  the  saliva  col- 
lect. 

The  sense  of  hearing  may  in  its  turn  be  affected  by  impres- 
sions on  many  other  parts  of  the  body ;  especially  in  diseases 
of  the  abdominal  viscera,  and  in  febrile  affections.  Here, 
also,  it  is  probable  that  the  central  organs  of  the  nervous 
system  are  the  media  through  which  the  impression  is  trans- 
mitted. 

SENSE    OF    TASTE. 

The  conditions  for  the  perception  of  taste  are  :  1,  the  pres- 
ence of  a  nerve  with  special  endowments ;  2,  the  excitation  of 
the  nerves  by  the  sapid  matters,  which  for  this  purpose  must 
be  in  a  state  of  solution.  The  nerves  concerned  in  the  produc- 
tion of  the  sense  of  taste  have  been  already  considered  (pp. 
431  and  437). 

The  mode  of  action  of  the  substances  which  excite  taste 
probably  consists  in  the  production  of  a  change  in  the  internal 
condition  of  the  gustatory  nerves ;  and,  according  to  the  dif- 
ference of  the  substances,  an  infinite  variety  of  changes  of  con- 
dition, and  consequently  of  tastes,  may  be  induced.  It  is  not, 
however,  necessary  for  the  manifestation  of  taste  that  sapid 
substances  in  solution  should  be  brought  into  contact  with  its 
nerves.  For  the  nerves  of  taste,  like  the  nerves  of  other 
special  senses,  may  have  their  peculiar  properties  excited  by 
various  other  kinds  of  irritation,  such  as  electricity  and  me- 
chanical impressions.  Thus  Henle  observed  that  a  small  cur- 
rent of  air  directed  upon  the  tongue  gives  rise  to  a  cool  saline 
taste,  like  that  of  saltpetre ;  and  Dr.  Baly  has  shown  that  a 
distinct  sensation  of  taste,  similar  to  that  caused  by  electricity, 
may  be  produced  by  a  smart  tap  applied  to  the  papillae  of  the 
tongue.  Moreover,  the  mechanical  irritation  of  the  fauces  and 
palate  produces  the  sensation  of  nausea,  which  is  probably 
only  a  modification  of  taste. 

The  matters  to  be  tasted  must  either  be  in  solution  or  be 
soluble  in  the  moisture  covering  the  tongue ;  hence  insoluble 
substances  are  usually  tasteless,  and  produce  merely  sensations 
of  touch.  Moreover,  for  the  perfect  action  of  a  sapid,  as  of  an 
odorous  substance,  it  is  necessary  that  the  sentient  surface 
should  be  moist.  Hence,  when  the  tongne  and  fauces  are 
dry,  sapid  substances,  even  in  solution,  are  with  difficulty 
tasted. 

The  principal,  but  not  exclusive  seat  of  the  sense  of  taste  is 
the  fauces  and  tongue. 


548  THE    SENSE    OF    TASTE. 

The  tongue  is  a  muscular  organ  covered  by  mucous  mem- 
brane ;  the  latter  resembling  other  mucous  membranes  (p. 
316)  in  essential  points  of  structure,  but  containing  certain 
parts,  the  papillae,  more  or  less  peculiar  to  itself;  peculiar, 
however,  in  details  of  structure  and  arrangement,  not  in  their 
nature.  The  tongue  is  beset  with  numerous  mucous  follicles 
and  glands.  Its  use  in  relation  to  mastication  and  deglutition 
has  already  been  considered  (p.  213). 

Besides  other  functions,  the  mucous  membrane  of  the  tongue 
serves  as  a  groundwork  for  the  ramification  of  the  abundant 
bloodvessels  and  nerves  which  the  tongue  receives,  and  affords 
insertion  to  the  extremities  of  the  muscular  fibres  of  which  the 
chief  substance  of  the  organ  is  composed. 

The  larger  papillae  of  the  tongue  are  thickly  set  over  the  an- 
terior two-thirds  of  its  upper  surface,  or  dor  sum  (Fig.  202),  and 
give  to  it  its  characteristic  roughness.  Their  greater  promi- 
nence than  those  of  the  skin  is  due  to  their  interspaces  not  being 
filled  up  with  epithelium,  as  the  interspaces  of  the  papillae  of 
the  skin  are.  The  papillae  of  the  tongue  present  several  di- 
versities of  form  ;  but  three  principal  varieties,  differing  both 
in  seat  and  general  characters,  may  usually  be  distinguished, 
namely,  the  circumvallate  or  calyciform,  the  funpiform,  and  the 
filiform  papillae.  Essentially  these  have  all  of  them  the  same 
structure,  that  is  to  say,  they  are  all  formed  by  a  projection 
of  the  mucous  membrane,  and  contain  special  branches  of 
bloodvessels  and  nerves.  In  details  of  structure,  however,  they 
differ  considerably  one  from  another. 

All  the  three  varieties  of  papillae  just  described  have  been 
commonly  regarded  as  simple  processes,  like  the  papillae  of  the 
skin;  but  Todd  and  Bowman  have  shown  that  the  surface  of 
each  kind  is  studded  by  minute  conical  processes  of  mucous 
membrane,  which  thus  form  secondary  papillae.  These  secon- 
dary papillae  also  occur  over  most  other  parts  of  the  tongue,  not 
occupied  by  the  compound  papillae,  and  extend  for  some  dis- 
tance behind  the  papillae  circumvallatae.  The  mucous  mem- 
brane immediately  in  front  of  the  epiglottis  is,  however,  free 
from  them.  They  are  commonly  buried  beneath  the  epithe- 
lium ;  hence  they  had  been  previously  overlooked. 

Circumvallate  or  Calyciform  Papillce. — These  papillae  (Fig. 
203),  eight  or  ten  in  number,  are  situate  in  two  V-shaped 
lines  at  the  base  of  the  tongue  (1,  1,  Fig.  202).  They  are 
circular  elevations,  from  o^th  to  y^th  of  an  inch  wide,  each 
with  a  central  depression,  and  surrounded  by  a  circular  fissure, 
at  the  outside  of  which  again  is  a  slightly  elevated  ring,  both 
the  central  elevation  and  the  ring  being  formed  of  close-set 
simple  papillae  (Fig.  203). 


STRUCTURE    OF    THE    TONGUE. 


549 


Fungiform  Papillae.— The  fungiform  papilla  (Fig.  204)  are 
scattered  chiefly  over  the  sides  and  tip,  and  sparingly  over  the 


FIG.  202. 


Papillar  surface  of  the  tongue,  with  the  fauces  and  tonsils  (from  Sappey).— 1,  1, 
circuruvallate  papillae,  in  front  of  2,  the  foramen  caecum;  3,  fungiform  papillae;  4, 
filiform  and  conical  papillae;  5,  transverse  and  oblique  rugae ;  6,  mucous  glands  at 
the  hase  of  the  tongue  and  in  the  fauces;  7,  tonsils;  8,  part  of  the  epiglottis;  9, 
median  glosso-epiglottidean  fold,  frsenum  epiglottidis. 

middle  of  the  dorsum,  of  the  tongue;  their  name  is  derived 
from  their  being  usually  narrower  at  their  base  than  at  their 


550 


THE    SENSE    OF    TASTE. 


summit.  They  also  consist  of  groups  of  simple  papillae,  each 
of  which  contains  in  its  interior  a  loop  of  capillary  blood- 
vessels, and  a  nerve-fibre. 


FIG.  203. 


Vertical  section  of  the  circumvallate  papillae  (from  Kolliker).  ij> . — A,  the  papillae  ; 
B,  the  surrounding  wall ;  a,  the  epithelial  covering ;  &,  the  nerves  of  the  papilla  and 
wall  spreading  towards  the  surface  ;  c,  the  secondary  papillae. 

Conical  or  Filiform  Papillae. — These,  which  are  the  most 
abundant  papillae,  are  scattered  over  the  whole  surface  of  the 
tongue,  but  especially  over  the  middle  of  the  dorsum. 


FIG.  204. 


a 


Surface  and  section  of  the  fungiform  papillae  (from  Kolliker,  after  Todd  and  Bow- 
man.)—A,  the  surface  of  a  fungiform  papilla,  partially  denuded  of  its  epithelium,  3^5. 
a,  epithelium.  B,  section  of  a  fungiform  papilla  with  the  bloodvessels  injected ; 
a,  artery ;  v,  vein ;  c,  capillary  loops  of  simple  papillae  in  the  neighboring  structure 
of  the  tongue. 

They  vary  in  shape  somewhat,  but  for  the  most  part  are 
conical  or  filiform,  and  covered  by  a  thick  layer  of  epidermis, 
which  is  arranged  over  them,  either  in  an  imbricated  manner, 
or  is  prolonged  from  their  surface  in  the  form  of  fine,  stiff 
projections,  hair-like  in  appearance,  and  in  some  instances  in 
structure  also  (Fig.  205).  From  their  peculiar  structure,  it 
seems  likely  that  these  papillae  have  a  mechanical  function,  or 


PAPILLJE    OF    THE    TONGUE. 


551 


one  allied  to  that  of  touch,  rather  than  of  taste ;  the  latter 
sense  being  probably  seated  especially  in  the  other  two  va- 
rieties of  papillae,  the  circumvallate  and  the  fungiform. 


FIG.  205. 


ft    7,    A   c'     a 

A.  Vertical  section  near  the  middle  of  the  dorsal  surface  of  the  tongue :  a,  a. 
Fungiform  papillae.    6.  Filiform  papillae,  with  their  hair-like  processes,    c.  Similar 
ones  deprived  of  their  epithelium,  magnified  2  diameters. 

B.  Filiform  compound  papillae:  a.  Artery,    v.  Vein.     c.  Capillary  loops  of  the 
secondary  papillae,    b.  Line  of  basement-membrane,    d.  Secondary  papillae,  deprived 
of  e,  e,  the  epithelium.    /.  Hair-like  processes  of  epithelium  capping  the  simple 
papillae,  magnified  25  diameters,    g.  Separated  nucleated  particles  of  epithelium, 
magnified  800  diameters. 

1,  2.  Hairs  found  on  the  surface  of  the  tongue.  3,  4,  5.  Ends  of  hair-like  epithelial 
processes,  showing  varieties  in  the  imbricated  arrangement  of  the  particles,  but  in 
all  a  coalescence  of  the  particles  towards  the  point.  5  incloses  a  soft  hair,  magnified 
160  diameters.  (Todd  and  Bowman.) 

The  epithelium  of  the  tongue  is  of  the  squamous  or  tessel- 
lated kind  (p.  34).     It  covers  every  part  of  the  surface ;  but 


552  THE    SENSE    OF    TASTE. 

over  the  fungiform  papillae  forms  a  thinner  layer  than  else- 
where, so  that  these  papillae  stand  out  more  prominently  than 
the  rest.  The  epithelium  covering  the  filiform  papillae  has 
been  shown  by  Todd  and  Bowman  to  have  a  singular  arrange- 
ment ;  being  extremely  dense  and  thick,  and,  as  before-men- 
tioned, projecting  from  their  sides  and  summits  in  the  form  of 
long,  stiff,  hair-like  processes.  Many  of  these  processes  bear 
a  close  resemblance  to  hairs,  and  some  actually  contain  minute 
hair-tubes.  Bloodvessels  and  nerves  are  supplied  freely  to  the 
papillae.  The  nerves  in  the  fungiform  and  circurnvallate  pa- 
pillae form  a  kind  of  plexus,  spreading  out  brush-wise  (Fig. 
203),  but  the  exact  mode  of  termination  of  the  nerve  filaments 
is  not  certainly  known. 

Such,  in  outline,  is  the  structure  of  the  sensitive  surface  of 
the  tongue.  But  the  tongue  is  not  the  only  seat  of  the  sense 
of  taste ;  for  the  results  of  experiments  as  well  as  ordinary  ex- 
perience show  that  the  soft  palate  and  its  arches,  the  uvula, 
tonsils,  and  probably  the  upper  part  of  the  pharynx,  are  en- 
dowed with  taste.  These  parts,  together  with  the  base  and 
posterior  parts  of  the  tongue,  are  supplied  with  branches  of  the 
glosso-pharyngeal  nerve,  and  evidence  has  been  already  ad- 
duced (p.  437  et  seq.)  that  the  sense  of  taste  is  conferred  upon 
them  by  this  nerve. 

In  most,  though  not  in  all  persons,  the  anterior  part  of  the 
tongue,  especially  the  edges  and  tip,  are  endowed  with  the 
sense  of  taste.  The  middle  of  the  dorsuni  is  only  feebly  en- 
dowed with  the  sense,  probably  because  of  the  density  and 
thickness  of  the  epithelium  covering  the  filiform  papillae  of 
this  part  of  the  tongue,  which  will  prevent  the  sapid  substances 
from  penetrating  to  their  sensitive  parts.  The  gustatory  prop- 
erty of  the  anterior  part  of  the  tongue  is  due,  as  already  said 
(p.  431 ),  to  the  lingual  branches  of  the  fifth  nerve. 

Besides  the  sense  of  taste,  the  tongue,  by  means  also  of  its 
papillae,  is  endued,  especially  at  its  sides  and  tip,  with  a  very 
delicate  and  accurate  sense  of  touch,  which  renders  it  sensible 
of  the  impressions  of  heat  and  cold,  pain  and  mechanical  pres- 
sure, and  consequently  of  the  form  of  surfaces.  The  tongue 
may  lose  its  common  sensibility,  and  still  retain  the  sense  of 
taste,  and  vice  versa.  This  fact  renders  it  probable  that,  al- 
though the  senses  of  taste  and  of  touch  may  be  exercised  by 
the  same  papillae  supplied  by  the  same  nerves,  yet  the  nervous 
conductors  for  these  two  different  sensations  are  distinct,  just 
as  the  nerves  for  smell  and  common  sensibility  in  the  nostrils 
are  distinct ;  and  it  is  quite  conceivable  that  the  same  nervous 
trunk  may  contain  fibres  differing  essentially  in  their  specific 
properties.  Facts  already  detailed  (p.  430)  seem  to  prove  that 


THE    SENSE    OF    TASTE.  553 

the  lingual  branch  of  the  fifth  nerve  is  the  seat  of  sensations  of 
taste  in  the  anterior  part  of  the  tongue:  and  it  is  also  certain, 
from  the  marked  manifestations  of  pain  to  which  its  division 
in  animals  gives  rise,  that  it  is  likewise  a  nerve  of  common  sen- 
sibility. The  glosso-pharyngeal  also  seems  to  contain  fibres 
both  of  common  sensation  and  of  the  special  sense  of  taste. 

The  concurrence  of  common  and  special  sensibility  in  the 
same  part  makes  it  sometimes  difficult  to  determine  whether 
the  impression  produced  by  a  substance  is  perceived  through 
the  ordinary  sensitive  fibres,  or  through  those  of  the  sense  of 
taste.  In  many  cases,  indeed,  it  is  probable  that  both  sets  of 
nerve-fibres  are  concerned,  as  when  irritating  acrid  substances 
are  introduced  into  the  mouth. 

The  impressions  on  the  mind  leading  to  the  perception  of 
taste  seem  to  result,  as  already  said,  from  certain  changes  in 
the  internal  condition  of  the  nerves  produced  by  the  contact 
of  sapid  substances  with  the  papillae  in  which  the  fibres  of  these 
nerves  are  distributed.  This  explanation,  obscure  though  it 
be,  may  account  generally  for  the  sense ;  but  the  variations  of 
taste  produced  by  different  substances  are  as  yet  inexplicable. 
In  the  case  of  hearing,  we  know  that  sounds  differ  from  one 
another  according  to  the  differences  in  the  number  of  undula- 
tions producing  them  ;  and  in  the  case  of  vision,  it  is  reasonably 
inferred  that  different  colors  result  from  differences  in  the  num- 
ber of  undulations,  or  in  the  rate  of  transit,  of  the  principle  of 
light.  But,  in  the  cases  of  taste  and  smell,  no  such  probable 
explanation  has  yet  been  offered.  It  would  appear,  indeed, 
from  the  experiments  of  Horn,  that  while  some  substances 
taste  alike  in  all  regions  of  the  tongue's  surface,  others  excite 
different  tastes,  according  as  they  are  applied  to  different  pa- 
pillae of  the  tongue.  This  observation,  if  confirmed,  would 
seem  to  show  that,  in  some  cases  at  least,  different  fibres  are 
capable  of  receiving  different  impressions  from  the  same  sapid 
substance. 

Much  of  the  perfection  of  the  sense  of  taste  is  often  due  to 
the  sapid  substances  being  also  odorous,  and  exciting  the  sim- 
ultaneous action  of  the  sense  of  smell.  This  is  shown  by  the 
imperfection  of  the  taste  of  such  substances  when  their  action 
on  the  olfactory  nerves  is  prevented  by  closing  the  nostrils. 
Many  fine  wines  lose  much  of  their  apparent  excellence  if  the 
nostrils  are  held  close  while  they  are  drunk. 

Very  distinct  sensations  of  taste  are  frequently  left  after  the 
substances  which  excited  them  have  ceased  to  act  on  the  nerve ; 
and  such  sensations  often  endure  for  a  long  time,  and  modify 
the  taste  of  other  substances  applied  to  the  tongue  afterwards. 
Thus,  the  taste  of  sweet  substances  spoils  the  flavor  of  wine, 


554  THE    SENSE    OF    TOUCH. 

the  taste  of  cheese  improves  it.  There  appears,  therefore,  to 
exist  the  same  relation  between  tastes  as  between  colors,  of 
which  those  that  are  opposed  or  complementary  render  each 
other  more  vivid,  though  no  general  principles  governing  this 
relation  have  been  discovered  in  the  case  of  tastes.  In  the  art 
of  cooking,  however,  attention  has  at  all  times  been  paid  to  the 
consonance  or  harmony  of  flavors  in  their  combination  or  order 
of  succession,  just  as  in  painting  and  music  the  fundamental 
principles  of  harmony  have  been  employed  empirically  while 
the  theoretical  laws  were  unknown. 

Frequent  and  continued  repetitions  of  the  same  taste  render 
the  perception  of  it  less  and  less  distinct,  in  the  same  way  that 
a  color  becomes  more  and  more  dull  and  indistinct  the  longer 
the  eye  is  fixed  upon  it.  Thus,  after  frequently  tasting  first 
one  and  then  the  other  of  two  kinds  of  wine,  it  becomes  im- 
possible to  discriminate  between  them. 

The  simple  contact  of  a  sapid  substance  with  the  surface  of 
the  gustatory  organ  seldom  gives  rise  to  a  distinct  sensation  of 
taste ;  it  needs  to  be  diffused  over  the  surface,  and  brought  into 
intimate  contact  with  the  sensitive  parts  by  compression,  fric- 
tion, and  motion  between  the  tongue  and  palate. 

The  sense  of  taste  seems  capable  of  being  excited  also  by  in- 
ternal causes,  such  as  changes  in  the  conditions  of  the  nerves 
or  nerve-centres,  produced  by  congestion  or  other  causes,  which 
excite  subjective  sensations  in  the  other  organs  of  sense.  But 
little  is  known  of  the  subjective  sensations  of  taste ;  for  it  is 
difficult  to  distinguish  the  phenomena  from  the  effects  of  ex- 
ternal causes,  such  as  changes  in  the  nature  of  the  secretions 
of  the  mouth. 

SENSE    OF    TOUCH. 

The  sense  of  touch  is  not  confined  to  particular  parts  of  the 
body  of  small  extent,  like  the  other  senses ;  on  the  contrary, 
all  parts  capable  of  perceiving  the  presence  of  a  stimulus  by 
ordinary  sensation  are,  in  certain  degrees,  the  seat  of  this  sense  ; 
for  touch  is  simply  a  modification  or  exaltation  of  common 
sensation  or  sensibility.  The  nerves  on  which  the  sense  of 
touch  depends  are,  therefore,  the  same  as  those  which  confer 
ordinary  sensation  on  the  different  parts  of  the  body,  viz.,  those 
derived  from  the  posterior  roots  of  the  nerves  of  the  spinal 
cord,  and  the  sensitive  cerebral  nerves. 

But,  although  all  parts  of  the  body  supplied  with  sensitive 
nerves  are  thus,  in  some  degree,  organs  of  touch,  yet  the  sense 
is  exercised  in  perfection  only  in  those  parts  the  sensibility  of 
which  is  extremely  delicate,  e.g.,  the  skin,  the  tongue, and  the 


THE    SENSE    OF    TOUCH.  555 

lips,  which  are  provided  with  abundant  papillae.  (See  chapter 
on  SKIN,  and  section  on  TASTE.) 

The  sensations  of  the  common  sensitive  nerves  have  as  pe- 
culiar a  character  as  those  of  any  other  organ  of  sense.  The 
sense  of  touch  renders  us  conscious  of  the  presence  of  a  stimu- 
lus, from  the  slightest  to  the  most  intense  degree  of  its  action, 
neither  by  sound,  nor  by  light,  nor  by  color,  but  by  that  inde- 
scribable something  which  we  call  feeling,  or  common  sensa- 
tion. The  modifications  of  this  sense  often  depend  on  the 
extent  of  the  parts  affected.  The  sensation  of  pricking,  for 
example,  informs  us  that  the  sensitive  particles  are  intensely 
affected  in  a  small  extent ;  the  sensation  of  pressure  indicates 
a  slighter  affection  of  the  parts  in  a  greater  extent,  and  to  a 
greater  depth.  It  is  by  the  depth  to  which  the  parts  are 
affected  that  the  feeling  of  pressure  is  distinguished  from  that 
of  mere  contact.  Schiff  and  Brown-Sequard  are  of  opinion 
that  common  sensibility  and  tactile  sensibility  manifest  them- 
selves to  the  individual  by  the  aid  of  different  sets  of  fibres. 
Dr.  Sieveking  has  arrived  at  the  same  conclusion  from  patho- 
logical observation. 

By  the  sense  of  touch  the  mind  is  made  acquainted  with 
the  size,  form,  and  other  external  characters  of  bodies.  And 
in  order  that  these  characters  may  be  easily  ascertained,  the 
sense  of  touch  is  especially  developed  in  those  parts  which  can 
be  readily  moved  over  the  surface  of  bodies.  Touch,  in  its 
more  limited  sense,  or  the  act  of  examining  a  body  by  the 
touch,  consists  merely  in  a  voluntary  employment  of  this  sense 
combined  with  movement,  and  stands  in  the  same  relation  to 
the  sense  of  touch,  or  common  sensibility,  generally,  as  the  act 
of  seeking,  following,  or  examining  odors,  does  to  the  sense  of 
smell.  Every  sensitive  part  of  the  body  which  can,  by  means 
of  movement,  be  brought  into  different  relations  of  contact 
with  external  bodies,  is  an  organ  of  "touch."  No  one  part, 
consequently,  has  exclusively  this  function.  The  hand,  how- 
ever, is  best  adapted  for  it,  by  reason  of  its  peculiarities  of 
structure, — namely,  its  capability  of  pronation  and  supination, 
which  enables  it,  by  the  movement  of  rotation,  to  examine  the 
whole  circumference  of  a  body ;  the  power  it  possesses  of  op- 
posing the  thumb  to  the  rest  of  the  hand ;  and  the  relative 
mobility  of  the  fingers.  Besides — the  hand,  and  especially 
the  fingers,  are  abundantly  endowed  with  papillce  and  touch- 
eorpuscles  (pp.  336,  337)  which  are  specially  necessary  for  the 
perfect  employment  of  this  sense. 

In  forming  a  conception  of  the  figure  and  extent  of  a  sur- 
face, the  mind  multiplies  the  size  of  the  hand  or  fingers  used 
in  the  inquiry  by  the  number  of  times  which  it  is  contained 


556  THE    SENSE    OF    TOUCH. 

in  the  surface  traversed  ;  and  by  repeating  this  process  with 
regard  to  the  different  dimensions  of  a  solid  body,  acquires  a 
notion  of  its  cubical  extent. 

The  perfection  of  the  sense  of  touch  on  different  parts  of 
the  surface  is  proportioned  to  the  power  which  such  parts  pos- 
sess of  distinguishing  and  isolating  the  sensations  produced  by 
two  points  placed  closed  together.  This  power  depends,  at 
least  in  part,  on  the  number  of  primitive  nerve-fibres  distributed 
to  the  part ;  for  the  fewer  the  primitive  fibres  which  an  organ 
receives,  the  more  likely  is  it  that  several  impressions  on  differ- 
ent contiguous  points  will  act  on  only  one  nervous  fibre,  and 
hence  be  confounded,  and  perhaps  produce  but  one  sensation. 
Experiments  to  determine  the  tactile  properties  of  different 
parts  of  the  skin,  as  measured  by  this  power  of  distinguishing 
distances,  were  made  by  E.  H.  Weber.  One  experiment  con- 
sisted in  touching  the  skin,  while  the  eyes  were  closed,  with 
the  points  of  a  pair  of  compasses  sheathed  with  cork,  and  in 
ascertaining  how  close  the  points  of  the  compasses  might  be 
brought  to  each  other,  and  still  be  felt  as  two  bodies.  He  ex- 
amined in  this  manner  nearly  every  part  of  the  surface  of  the 
body,  and  has  given  tables  showing  the  relative  degrees  of  sen- 
sibility of  different  parts.  Experiments  of  a  similar  kind 
have  been  performed  also  by  Valentin ;  and,  among  the  nu- 
merous results  obtained  by  both  these  investigators,  it  appears 
that  the  extremity  of  the  third  finger,  and  the  point  of  the 
tongue  are  the  parts  most  sensitive :  a  distance  of  as  little  as 
half  a  line  being  here  distinguished.  Next  in  sensitiveness  to 
these  is  the  mucous  surface  of  the  lips,  which  can  perceive  the 
two  points  of  the  compass  when  separated  to  the  distance  of 
about  a  line  and  a  half:  on  the  dorsum  of  the  tongue  they  re- 
quire to  be  separated  two  lines.  The  parts  in  which  the  sense 
of  touch  is  least  acute  are  the  neck,  the  middle  of  the  back, 
the  middle  of  the  arm,  and  the  middle  of  the  thigh,  on  which 
the  points  of  the  compass  have  to  be  separated  to  the  distance 
of  thirty  lines  to  be  perceived  as  distinct  points  (Weber). 
Other  parts  of  the  body  possess  various  degrees  of  sensibility 
intermediate  between  the  above  extremes. 

A  sensation  in  a  part  endowed  with  touch  appears  to  the 
mind  to  be,  cceteris  paribus,  more  intense  when  it  is  excited  in 
a  large  extent  of  surface  than  when  it  is  confined  to  a  small 
space.  The  temperature  of  water  into  which  he  dipped  his 
whole  hand,  appeared  to  Weber  to  be  higher  than  that  of 
water  of  really  higher  temperature,  in  which  he  immersed 
only  one  finger  of  the  other  hand.  Similar  observations  may 
be  made  by  persons  bathing  in  warm  or  cold  water. 

Part  of  the  ideas  which  we  obtain  of  the  conditions  of  ex- 


THE    SENSE    OF    TOUCH.  557 

ternal  bodies  is  derived  through  the  peculiar  sensibility  with 
which  muscles  are  endowed — -the  sensibility  by  which  we  are 
made  acquainted  with  their  position,  and  the  degree  of  their 
contraction.  By  this  sensation,  we  are  enabled  to  estimate  the 
degree  of  force  exerted  in  resisting  pressure  or  in  raising 
weights.  The  estimate  of  weight  by  muscular  effort  is  more 
accurate  than  that  by  pressure  on  the  skin,  according  to  Weber, 
who  states  that  by  the  former  a  difference  between  two  weights 
may  be  detected  when  one  is  only  one-twentieth  or  one-fifteenth 
less  than  the  other.  It  is  not  the  absolute,  but  the  relative, 
amount  of  the  difference  of  weight  which  we  have  thus  the 
faculty  of  perceiving. 

It  is  not,  however,  certain,  that  our  idea  of  the  amount  of 
muscular  force  used  is  derived  solely  from  sensation  in  the 
muscles.  We  have  the  power  of  estimating  very  accurately 
beforehand,  and  of  regulating,  the  amount  of  nervous  influ- 
ence necessary  for  the  production  of  a  certain  degree  of  move- 
ment. When  we  raise  a  vessel,  with  the  contents  of  which  we 
are  not  acquainted,  the  force  we  employ  is  determined  by  the 
idea  we  have  conceived  of  its  weight.  If  it  should  happen  to 
contain  some  very  heavy  substance,  as  quicksilver,  we  shall 
probably  let  it  fall ;  the  amount  of  muscular  action,  or  of  ner- 
vous energy,  which  we  had  exerted,  being  insufficient.  The 
same  thing  occurs  sometimes  to  a  person  descending  stairs  in 
the  dark ;  he  makes  the  movement  for  the  descent  of  a  step 
which  does  not  exist.  It  is  possible  that  in  the  same  way  the 
idea  of  weight  and  pressure  in  raising  bodies,  or  in  resisting 
forces,  may  in  part  arise  from  a  consciousness  of  the  amount 
of  nervous  energy  transmitted  from  the  brain  rather  than  from 
a  sensation  in  the  muscles  themselves.  The  mental  conviction 
of  the  inability  longer  to  support  a  weight  must  also  be  dis- 
tinguished from  the  actual  sensation  of  fatigue  in  the  muscles. 

So,  with  regard  to  the  ideas  derived  from  sensation  of  touch 
combined  with  movements,  it  is  doubtful  how  far  the  conscious- 
ness of  the  extent  of  muscular  movement  is  obtained  from  sen- 
sations in  the  muscles  themselves.  The  sensation  of  movement 
attending  the  motions  of  the  hand  is  very  slight ;  and  persons 
who  do  not  know  that  the  action  of  particular  muscles  is  nec- 
essary for  the  production  of  given  movements,  do  not  suspect 
that  the  movement  of  the  fingers,  for  example,  depends  on  an 
action  in  the  forearm.  The  mind  has,  nevertheless,  a  very 
definite  knowledge  of  the  changes  of  position  produced  by 
movements ;  and  it  is  on  this  that  the  ideas  which  it  conceives 
of  the  extension  and  form  of  a  body  are  in  great  measure 
founded. 

In  order  that  an  impression  made  on  a  sensitive  surface 

47 


558  THE    SENSE    OF    TOUCH. 

may  be  perceived,  it  is  necessary  that  there  should  exist  a 
reciprocal  influence  between  the  mind  and  the  sense  of  touch ; 
for,  if  the  mind  does  not  thus  co-operate,  the  organic  condi- 
tions for  the  sensation  may  be  fulfilled,  but  it  remains  unper- 
ceived.  Moreover,  the  distinctness  and  intensity  of  a  sensa- 
tion in  the  nerves  of  touch  depend,  in  great  measure,  on  the 
degree  in  which  the  mind  co-operates  for  its  perception.  A 
painful  sensation  becomes  more  intolerable  the  more  the  at- 
tention is  directed  to  it :  thus,  a  sensation  in  itself  inconsider- 
able, as  an  itching  in  a  very  small  spot  of  the  skin,  may  be 
rendered  very  troublesome  and  enduring. 

As  every  sensation  is  attended  with  an  idea,  and  leaves 
behind  it  an  idea  in  the  mind  which  can  be  reproduced  at 
will,  we  are  enabled  to  compare  the  idea  of  a  past  sensation 
with  another  sensation  really  present.  Thus  we  can  compare 
the  weight  of  one  body  with  another  which  we  had  previously 
felt,  of  which  the  idea  is  retained  in  our  mind.  Weber  was 
indeed  able  to  distinguish  in  this  manner  between  tempera- 
tures, experienced  one  after  the  other,  better  than  between 
temperatures  to  which  the  two  hands  were  simultaneously 
subjected.  This  power  of  comparing  present  with  past  sensa- 
tions diminishes,  however,  in  proportion  to  the  time  which  has 
elapsed  between  them. 

The  after-sensations  left  by  impressions  on  nerves  of  common 
sensibility  or  touch  are  very  vivid  and  durable.  As  long  as 
the  condition  into  which  the  stimulus  has  thrown  the  organ 
endures,  the  sensation  also  remains,  though  the  exciting  cause 
should  have  long  ceased  to  act.  Both  painful  and  pleasurable 
sensations  afford  many  examples  of  this  fact. 

The  law  of  contrast,  which  we  have  shown  modifies  the  sen- 
sations of  vision,  prevails  here  also.  After  the  body  has  been 
exposed  to  a  warm  atmosphere,  a  degree  of  temperature  a  very 
little  lower,  which  would  under  other  circumstances  appear 
warm,  produces  the  sensation  of  cold;  and  a  sudden  change  to 
the  extent  of  a  few  degrees  from  a  cold  temperature  to  one  less 
severe,  will  produce  the  sensation  of  warmth.  Heat  and  cold 
are,  therefore,  relative  terms ;  for  a  particular  state  of  the 
sentient  organs  causes  what  would  otherwise  be  warmth  to 
appear  cold.  So,  also  a  diminution  in  the  intensity  of  a  long- 
continued  pain  gives  pleasure,  even  though  the  degree  of  pain 
that  remains  would  in  the  healthy  state  have  seemed  intoler- 
able. 

Subjective  sensations,  or  sensations  dependent  on  internal 
causes,  are  in  no  sense  more  frequent  than  in  the  sense  of 
touch.  All  the  sensations  of  pleasure  and  pain,  of  heat  and 
cold,  of  lightness  and  weight,  of  fatigue,  &c.,  may  be  produced 


GENERATION    AND    DEVELOPMENT.          559 

by  internal  causes.  Neuralgic  pains,  the  sensation  of  rigor, 
formication  or  the  creeping  of  ants,  and  the  states  of  the  sexual 
organs  occurring  during  sleep,  afford  striking  examples  of  sub- 
jective sensations. 

The  mind,  also,  has  a  remarkable  power  of  exciting  sensa- 
tions in  the  nerves  of  common  sensibility ;  just  as  the  thought 
of  the  nauseous  excites  sometimes  the  sensation  of  nausea,  so 
the  idea  of  pain  gives  rise  to  the  actual  sensation  of  pain  in  a 
part  predisposed  to  it.  The  thought  of  anything  horrid  excites 
the  sensation  of  shuddering;  the  feelings  of  eager  expectation, 
of  pathetic  emotion,  of  enthusiasm,  excite  in  some  persons  a 
sensation  of  "  concentration"  at  the  top  of  the  head,  and  of  cold 
trickling  through  the  body ;  fright  causes  sensations  to  be  felt 
in  many  parts  of  the  body ;  and  even  the  thought  of  tickling 
excites  that  sensation  in  individuals  very  susceptible  of  it, 
when  they  are  threatened  with  it  by  the  movements  of  another 
person.  These  sensations  from  internal  causes  are  most  fre- 
quent in  persons  of  excitable  nervous  systems,  such  as  the 
hypochondriacal  and  the  hysterical,  of  whom  it  is  usual  to  say 
that  their  pains  are  imaginary.  If  by  this  is  meant  that  their 
pains  exist  in  their  imagination  merely,  it  is  certainly  quite  in- 
correct. Pain  is  never  imaginary  in  this  sense ;  but  is  as  truly 
pain  when  arising  from  internal  as  from  external  causes ;  the 
idea  of  pain  only  can  be  unattended  with  sensation,  but  of  the 
mere  idea  no  one  will  complain.  Still,  it  is  quite  certain  that 
the  imagination  can  render  pain  that  already  exists  more  in- 
tense and  can  excite  it  when  there  is  a  disposition  to  it. 


CHAPTER  XX. 

GENERATION  AND  DEVELOPMENT. 

THE  several  organs  and  functions  of  the  human  body  which 
have  been  considered  in  the  previous  chapters,  have  relation 
to  the  individual  being.  We  have  now  to  consider  those 
organs  and  functions  which  are  destined  for  the  propagation 
of  the  species.  These  comprise  the  several  provisions  made 
for  the  formation,  impregnation,  and  development  of  the 
ovum,  from  which  the  embryo  or  foetus  is  produced  and  gradu- 
ally perfected  into  a  fully-formed  human  being. 

The  organs  concerned  in  effecting  these  objects  are  named 


560          GENERATION    AND    DEVELOPMENT. 

the  geDerative  organs,  or  sexual  apparatus,  since  part  belong 
to  the  male  and  part  to  the  female  sex. 

Generative  Organs  of  the  Female. 

The  female  organs  of  generation  consist  of  two  ovaries, 
whose  function  is  the  formation  of  ova ;  of  a  Fallopian  tube, 
or  oviduct,  connected  with  each  ovary,  for  the  purpose  of  con- 
ducting the  ovum  from  the  ovary  to  the  uterus  or  cavity  in 
which,  if  impregnated,  it  is  retained  until  the  embryo  is  fully 
developed,  and  fitted  to  maintain  its  existence,  independently 
of  internal  connection  with  the  parent;  and,  lastly,  of  a  canal, 
of  vagina,  with  its  appendages,  for  the  reception  of  the  male 
generative  organ  in  the  act  of  copulation,  and  for  the  subse- 
quent discharge  of  the  foetus. 

FIG.  206. 


Diagrammatic  view  of  the  uterus  and  its  appendages,  as  seen  from  behind  (from 
Quain).  %.— The  uterus  and  upper  part  of  the  vagina  have  been  laid  open  by  re- 
moving the  posterior  wall ;  the  Fallopian  tube,  round  ligament,  and  ovarian  liga- 
ment have  been  cut  short,  and  the  broad  ligament  removed  on  the  left  side  ;  u.  the 
upper  part  of  the  uterus;  c,  the  cervix  opposite  the  os  internum  ;  the  triangular 
shape  of  the  uterine  cavity  is  shown,  and  the  dilatation  of  the  cervical  cavity  with 
the  rugae  termed  arbor  vitse  ;  v,  upper  part  of  the  vagina;  od,  Fallopian  tube  or  ovi- 
duct ;  the  narrow  communication  of  its  cavity  with  that  of  the  cornu  of  the  uterus 
on  each  side  is  seen  ;  /,  round  ligament ;  lo,  ligament  of  the  ovary ;  o,  ovary ;  t,  wide 
outer  part  of  the  right  Fallopian  tube  ;fi,  its  fimbriated  extremity;  po,  parovarium; 
A,  one  of  the  hydatids  frequently  found  connected  with  the  broad  ligament. 

The  ovaries  are  two  oval  compressed  bodies,  situated  in  the 
cavity  of  the  pelvis,  one  on  each  side,  inclosed  in  the  folds  of 
the  broad  ligament.  Each  ovary  is  attached  to  the  uterus  by 


FEMALE  ORGANS  OF  GENERATION. 


561 


a  narrow  fibrous  cord  (the  ligament  of  the  ovary),  and,  more 
slightly,  to  the  Fallopian  tube  by  one  of  the  fimbrise,  into 
which  the  walls  of  the  extremity  of  the  tube  expand. 

The  ovary  is  enveloped  by  a  capsule  of  dense  nbro-cellular 
tissue,  which  again  is  surrounded  by  peritoneum.  The  internal 
structure  of  the  organ  consists  of  a  peculiar  soft  fibrous  tissue, 
or  stroma,  abundantly  supplied  with  bloodvessels,  and  having 
imbedded  in  it,  in  various  stages  of  development,  numerous 
minute  follicles  or  vesicles,  the  Graafian  vesicles,- or  sacculi, 
containing  the  ova  (Fig.  207).  A  further  account  of  the 

FIG.  207. 


View  of  a  section  of  the  prepared  ovary  of  the  cat  (from  Schron)  6. — 1,  outer  cover- 
ing and  free  border  of  the  ovary ;  1',  attached  border ;  2,  the  ovarian  stroma,  present- 
ing a  fibrous  and  vascular  structure ;  3,  granular  substance  lying  external  to  the 
fibrous  stroma;  4,  bloodvessels ;  5,  ovigerms  in  their  earliest  stages  occupying  a 
part  of  the  granular  layer  near  the  surface ;  6,  ovigerms  which  have  begun  to  enlarge 
and  to  pass  more  deeply  into  the  ovary;  7,  ovigerms  round  which  the  Graafian 
follicle  and  tunica  granulosa  are  now  formed,  and  which  have  passed  somewhat 
deeper  into  the  ovary  and  are  surrounded  by  the  fibrous  stroma  ;  8,  more  advanced 
Graafian  follicle  with  the  ovum  imbedded  in  the  layer  of  cells  constituting  the  pro- 
ligerous  disk;  9,  the  most  advanced  follicle  containing  the  ovum,  &c. ;  9',  a  follicle 
from  which  the  ovum  has  accidentally  escaped  ;  10,  corpus  luteum. 

Graafian  vesicles  and  of  their  contained  ova  will  be  presently 
given. 

The  Fallopian  tubes  are  about  four  inches  in  length,  and  ex- 
tend between  the  ovaries  and  the  upper  angles  of  the  uterus. 
At  the  point  of  attachment  to  the  uterus,  the  Fallopian  tube 
is  very  narrow ;  but  in  its  course  to  the  ovary  it  increases  to 
about  a  line  and  a  half  in  thickness ;  at  its  distal  extremity, 
which  is  free  and  floating,  it  bears  a  number  of  fimbrice,  one 
of  which,  longer  than  the  rest,  is  attached  to  the  ovary.  The 


562          GENERATION    AND    DEVELOPMENT. 

canal  by  which  each  Fallopian  tube  is  traversed  is  narrow, 
especially  at  its  point  of  entrance  into  the  uterus,  at  which  it 
will  scarcely  admit  a  bristle ;  its  other  extremity  is  wider,  and 
opens  into  the  cavity  of  the  abdomen,  surrounded  by  the  zone 
of  fimbrise.  Externally,  the  Fallopian  tube  is  invested  with 
peritoneum  ;  internally,  its  canal  is  lined  with  mucous  mem- 
brane, covered  with  ciliary  epithelium  (p.  37) :  between  the 
peritoneal  and  mucous  coats,  the  walls  are  composed  like  those 
of  the  uterus,  of  fibrous  tissue  and  organic  muscular  fibres 
(pp.  456-7). 

The  uterus  (u,  c,  Fig.  206)  is  a  somewhat  pyriform,  fibrous 
organ,  with  a  central  cavity  lined  with  mucous  membrane.  In 
the  unimpregnated  state  it  is  about  three  inches  in  length,  two 
in  breadth  at  its  upper  part,  or  fundus,  but  at  its  lower  pointed 
part  or  neck,  only  about  half  an  inch.  The  part  between  the 
fundus  and  neck  is  termed  the  body  of  the  uterus;  it  is  about 
an  inch  in  thickness.  The  walls  of  the  organ  are  composed  of 
dense  fibro-cellular  tissue,  with  which  are  intermingled  fibres 
of  organic  muscle :  in  the  impregnated  state  the  latter  are  much 
developed  and  increased  in  number.  The  cavity  of  the  uterus 
corresponds  in  form  to  that  of  the  organ  itself:  it  is  very  small 
in  the  unimpregnated  state ;  the  sides  of  its  mucous  surface 
being  almost  in  contact,  and  probably  only  separated  from 
each  other  by  mucus.  Into  its  upper  part,  at  each  side,  opens 
the  canal  of  the  corresponding  Fallopian  tube:  below,  it  com- 
municates with  the  vagina  by  a  fissure-like  opening  in  its  neck, 
the  os  uteri,  the  margins  of  which  are  distinguished  into  two 
lips,  an  anterior  and  posterior.  In  the  mucous  membrane  of 
the  cervix  are  found  several  mucous  follicles,  termed  ovula  or 
glaudulse  Nabothi:  they  probably  form  the  jelly-like  substance 
by  which  the  os  uteri  is  usually  found  closed. 

The  vagina  is  a  membranous  canal,  six  or  eight  inches  long, 
extending  obliquely  downwards  arid  forwards  from  the  neck 
of  the  uterus,  which  it  embraces,  to  the  external  organs  of 
generation.  It  is  lined  with  mucous  membrane,  which,  in  the 
ordinary  contracted  state  of  the  canal,  is  thrown  into  trans- 
verse folds.  External  to  the  mucous  membrane,  the  walls  of 
the  vagina  are  constructed  of  fibro-cellular  tissue,  within  which, 
especially  around  the  lower  part  of  the  tube,  is  a  layer  of 
erectile  tissue.  The  lower  extremity  of  the  vagina  is  embraced 
by  an  orbicular  muscle,  the  constrictor  vaginae ;  its  external 
orifice,  in  the  virgin,  is  partially  closed  by  a  fold  or  ring  of 
mucous  membrane,  termed  the  hymen.  The  external  organs 
of  generation  consist  of  the  clitoris,  a  small  elongated  body, 
situated  above  and  in  the  middle  line,  and  constructed,  like 
the  male  penis,  of  two  erectile  corpora  cavernosa,  but  unlike 


THE    UNIMPREGNATED    OVUM.  563 

it,  without  a  corpus  spongiosum,  and  not  perforated  by  the 
urethra ;  of  two  folds  of  mucous  membrane,  termed  labia  in- 
terna,  or  nymphce;  and,  in  front  of  these,  of  two  other  folds, 
the  labia  externa,  or  pudenda,  formed  of  the  external  integu- 
ment, and  lined  internally  by  mucous  membrane.  Between 
the  nymphse  and  beneath  the  clitoris  is  an  angular  space, 
termed  the  vestibule,  at  the  centre  of  whose  base  is  the 
orifice  of  the  meatus  urinarius.  Numerous  mucous  follicles 
are  scattered  beneath  the  mucous  membrane  composing  these 
parts  of  the  external  organs  of  generation ;  and  at  the  side  of 
the  fore  part  of  the  vagina,  are  two  large  lobulated  glands, 
named  vulvo-vaginal,  or  Duverney's  glands,  which  are  anal- 
ogous to  Cowper's  glands  in  the  male. 

Having  given  this  general  outline  of  the  several  parts  which, 
in  the  female,  contribute  to  the  reproduction  of  the  species,  it 
will  now  be  necessary  to  examine  successively  the  formation, 
discharge,  impregnation,  and  development  of  the  ovum,  to 
which  these  several  parts  are  subservient. 

Unimpregnated  Ovum. 

If  the  structure  and  formation  of  the  human  ovary  be  ex- 
amined at  any  period  between  early  infancy  and  advanced 
age,  but  especially  during  that  period  of  life  in  which  the  power 
of  conception  exists,  it  will  be  found  to  contain,  on  an  average, 
from  fifteen  to  twenty  small  vesicles  or  membranous  sacs  of 
various  sizes;  these  have  been  already  alluded  to  as  the  follicles 
or  vesicles  of  De  Graaf,  the  anatomist  who  first  accurately  de- 
scribed them  ;  they  are  also  sometimes  called  ovisacs.  At  their 
first  formation,  the  Graafian  vesicles,  according  to  Schron,  are 
near  the  surface  of  the  stroma  of  the  ovary,  but  subsequently 
become  more  deeply  placed ;  and  again,  as  they  increase  in 
size,  make  their  way  towards  the  surface.  When  mature,  they 
form  little  prominences  on  the  exterior  of  the  ovary,  covered 
only  by  the  peritoneum.  Each  follicle  has  an  external  mem- 
branous envelope,  composed  of  fine  fibro-cellular  tissue,  and 
connected  with  the  surrounding  stroma  of  the  ovary  by  net- 
works of  bloodvessels  (Fig.  208).  This  envelope  or  tunic  is 
lined  with  a  layer  of  nucleated  cells,  forming  a  kind  of  epi- 
thelium or  internal  tunic,  and  named  membrana  granulosa. 
The  cavity  of  the  follicle  is  filled  with  an  albuminous  fluid  in 
which  microscopic  granules  float;  and  it  contains  also  the  ovum 
or  ovule. 

The  ovum  is  a  minute  spherical  body  situated,  in  immature 
follicles,  near  the  centre ;  but  in  those  nearer  maturity,  in  con- 
tact with  the  membrana  granulosa  at  that  part  of  the  follicle 


564          GENERATION    AND    DEVELOPMENT. 

which  forms  a  prominence  on  the  surface  of  the  ovary.  The 
cells  of  the  membrana  granulosa  are  at  that  point  more  numer- 
ous than  elsewhere,  and  are  heaped  around  the  ovum,  forming 
a  kind  of  granular  zone,  the  discus  proligerus  (Fig.  208.) 

In  order  to  examine  an  ovum,  one  of  the  Graafian  vesicles, 
it  matters  not  whether  it  be  of  small  size  or  arrived  at  maturity, 
should  be  pricked,  and  the  contained  fluid  received  upon  a 
piece  of  glass.  The  ovum  then,  being  found  in  the  midst  of 
the  fluid  by  means  of  a  simple  lens,  .may  be  further  examined 
with  higher  microscopic  powers.  Owing  to  its  globular  form, 
however,  its  structure  cannot  be  seen  until  it  is  subjected  to 
gentle  pressure. 

The  human  ovum  is  extremely  small,  measuring  according 
to  Bischoff,  from  5|(j  to  ^-Q-  of  an  inch.  Its  external  invest- 
ment is  a  transparent  membrane,  about  ^QQ  of  an  inch  in 
thickness,  which  under  the  microscope,  appears  as  a  bright 
ring  (Fig.  209),  bounded  externally  and  internally  by  a  dark 


FIG.  208. — Section  of  the  Graafian  vesicle  of  a  Mammal,  after  Von  Baer.  1.  Stroma 
of  the  ovary  with  bloodvessels.  2.  Peritoneum.  3  and  4.  Layers  of  the  external 
coat  of  the  Graafian  vesicle.  5.  Membrana  granulosa.  6.  Fluid  of  the  Graafian 
vesicle.  7.  Granular  zone,  or  discus  proligerus,  containing  the  ovum  (8). 

Fitt.  209.— Ovum  of  the  sow,  after  Barry.  1.  Germinal  spot.  2.  Germinal  vesicle. 
3.  Yelk.  4.  Zona  pellucida.  5.  Discus  proligerus.  6.  Adherent  granules  or  cells. 

outline :  it  is  called  the  zona  pellucida,  or  vitelline  membrane. 
It  adheres  externally  to  the  heap  of  cells  constituting  the  dis- 
cus proligerus. 

Within  this  transparent  investment  or  zona  pellucida,  and 
usually  in  close  contact  with  it,  lies  the  yelk  or  vitellus,  which 
is  composed  of  granules  and  globules  of  various  sizes,  imbed- 
ded in  a  more  or  less  fluid  substance.  The  smaller  granules, 
which  are  the  more  numerous,  resemble  in  their  appearance, 
as  well  as  their  constant  motion,  pigment-granules.  The  larger 
granules  or  globules,  which  have  the  aspect  of  fat-globules,  are 
in  greatest  number  at  the  periphery  of  the  yelk.  The  number 
of  the  granules  is,  according  to  Bischoff,  greatest  in  the  ova  of 


DEVELOPMENT    OF    OVUM. 


565 


carnivorous  animals.     In  the  human  ovum  their  quantity  is 
comparatively  small. 

In  the  substance  of  the  yelk  is  imbedded  the  germinal  vesicle, 
or  vesicula  germinativa  (Figs.  209,  210).  This  vesicle  is  of 
greatest  relative  size  in  the  smallest  ova,  and  is  in  them  sur- 
rounded closely  by  the  yelk,  nearly  in  the  centre  of  which  it 
lies.  During  the  development  of  the  ovum,  the  germinal  vesicle 
increases  in  size  much  less  rapidly  than  the  yelk,  and  comes 
to  be  placed  near  to  its  surface.  Its  size  in  the  human  ovum 
has  not  yet  been  ascertained,  owing  to  the  difficulty  of  isolat- 
ing it;  but  it  is  probably  about  ^^  of  an  inch  in  diameter. 
It  consists  of  a  fine,  transparent,  structureless  membrane,  con- 


Diagram  of  a  Graafian  vesicle,  containing  an  ovum.  1.  Stroma  or  tissue  of  the 
ovary.  2  and  3.  External  and  internal  tunics  of  the  Graafian  vesicle.  4.  Cavity  of 
the  vesicle.  5.  Thick  tunic  of  the  ovum  or  yelk-sac.  6.  The  yelk.  7.  The  germinal 
vesicle.  8.  The  germinal  spot. 


taining  a  clear,  watery  fluid,  in  which  are  sometimes  a  few 
granules  ;  and  at  that  part  of  the  periphery  of  the  germinal 
vesicle  which  is  nearest  to  the  periphery  of  the  yelk  is  situated 
the  germinal  spot  (macula  germinativa},  a  finely  granulated  sub- 
stance, of  a  yellowish  color,  strongly  refracting  the  rays  of 
light,  and  measuring,  in  the  Mammalia  generally,  from  ^g1^ 
to  ^7770  °f  an  iucn  (Wagner). 

Such  are  the  parts  of  which  the  Graafian  follicle  and  its 
contents,  including  the  ovum,  are  composed.  The  diagram 
(Fig.  210)  represents  them  in  their  relative  positions  when 
mature.  With  regard  to  the  mode  and  order  of  development 
of  these  parts  there  is  considerable  uncertainty;  but  it  seems 
most  likely  that  the  ovum  is  formed  before  the  Graafian  vesi- 
cle or  ovisac. 

48 


566          GENERATION    AND    DEVELOPMENT. 

With  regard  to  the  parts  of  the  ovum  first  formed,  it  appears 
certain  that  the  formation  of  the  germinal  vesicle  precedes 
that  of  the  yelk  and  zona  pellucida,  or  vitelline  membrane. 
Whether  the  germinal  spot  is  formed  first,  and  the  germinal 
vesicle  afterwards  developed  around  it,  cannot  be  decided  in 
the  case  of  vertebrate  animals ;  but  the  observations  of  Kol- 
liker  and  Bagge  on  the  development  of  the  ova  of  intestinal 
worms  show  that  in  these  animals,  the  first  step  in  the  process 
is  the  production  of  round  bodies  resembling  the  germinal 
spots  of  ova,  the  germinal  vesicles  being  subsequently  devel- 
oped around  these  in  the  form  of  transparent  membranous 
cells. 

The  more  important  changes  that  take  place  in  the  ovum 
next  to  the  formation  of  these  its  essential  component  parts, 
consist  in  alterations  of  the  size  and  position  of  these  parts 
with  relation  to  each  other,  and  of  the  ovum  itself  with  rela- 
tion to  the  Graafian  vesicle,  and  in  the  more  complete  elabora- 
tion of  the  yelk.  The  earlier  the  stage  of  development  the 
larger  is  the  germinal  vesicle  in  relation  to  the  whole  ovum, 
and  of  the  ovum  in  relation  to  the  Graafian  vesicle.  For,  as 
the  ovum  becomes  mature,  although  all  these  parts  increase  in 
size,  the  Graafian  vesicle  enlarges  most,  and  the  germinal 
vesicle  least.  Changes  take  place  also  in  the  position  of  the 
parts.  The  ovum  at  first  occupies  the  centre  of  the  Graafian 
vesicle,  but  subsequently  is  removed  to  its  periphery.  The 
germinal  vesicle,  too,  which  in  young  ova  is  in  the  centre  of 
the  yelk,  is  in  mature  ova  found  at  the  periphery. 

The  change  of  position  of  the  ovum,  from  the  centre  to  the 
periphery  of  the  Graafian  vesicle,  is  possibly  connected  with 
the  formation  of  the  membrana  granulosa  which  lines  the 
vesicle.  For,  according  to  Valentin,  at  a  very  early  period, 
the  contents  of  the  vesicle  between  its  wall  and  the  ovum  are 
almost  wholly  formed  of  granules ;  but  in  the  process  of  growth 
a  clear  fluid  collects  in  the  centre  of  the  vesicle,  and  the 
granules,  which  from  the  first  have  a  regular  arrangement, 
are  pushed  outwards,  and  form  the  membrana  granulosa. 
Now,  as  the  mature  ovum  lies  imbedded  in  a  thickened  por- 
tion of  the  membrana  granulosa,  it  is  possible  that  when  the 
elementary  parts  of  this  membrane  are  pushed  outwards,  in 
the  way  just  described,  the  ovum  is  carried  with  them  from 
the  centre  to  the  periphery  of  the  follicle.  While  the  changes 
here  described  take  place,  the  zona  pellucida  increases  in  thick- 
ness. 

According  to  Bischoff,  the  number  of  the  granules  of  the 
yelk  is  greater  the  more  mature  the  ovum,  consequently  the 
the  yelk  is  more  opaque  in  the  mature,  and  more  transparent 


DISCHARGE    OF    THE    OVUM.  567 

in  the  immature  ova.  The  matter  in  which  the  granules  are 
contained  is  fluid  in  the  immature  ova  of  all  animals  ;  in  some 
it  remains  so ;  but  in  others,  as  the  human  ovum,  it  subse- 
quently becomes  a  consistent  gelatinous  substance. 

From  the  earliest  infancy,  and  through  the  whole  fruitful 
period  of  life,  there  appears  to  be  a  constant  formation,  devel- 
opment, and  maturation  of  Graafian  vesicles,  with  their  con- 
tained ova.  Until  the  period  of  puberty,  however,  the  pro- 
cess is  comparatively  inactive ;  for  previous  to  this  period,  the 
ovaries  are  small  and  pale,  the  Graafian  vesicles  in  them  are 
very  minute,  few  in  number,  and  probably  never  attain  full 
development,  but  soon  shrivel  and  disappear,  instead  of  burst- 
ing, as  matured  follicles  do ;  the  contained  ova  are  also  inca- 
pable of  being  impregnated.  But,  coincident  with  the  other 
changes  which  occur  in  the  body  at  the  time  of  puberty,  the 
ovaries  enlarge,  and  become  very  vascular,  the  formation  of 
Graafian  vesicles  is  more  abundant,  the  size  and  degree  of 
development  attained  by  them  are  greater,  and  the  ova  are 
capable  of  being  fecundated. 

Discharge  of  the  Ovum. 

In  the  process  of  development  of  individual  vesicles,  it  has 
been  already  observed,  that  as  each  increases  in  size,  it  gradu- 
ally approaches  the  surface  of  the  ovary,  and  when  fully  ripe 
or  mature,  forms  a  little  projection  on  the  exterior.  Coinci- 
dent with  the  increase  of  size,  caused  by  the  augmentation  of 
its  liquid  contents,  the  external  envelope  of  the  distended 
vesicle  becomes  very  thin  and  eventually  bursts.  By  this 
means,  the  ovum  and  fluid  contents  of  the  Graafian  vesicle 
are  liberated,  and  escape  on  the  exterior  of  the  ovary,  whence 
they  pass  into  the  Fallopian  tube,  the  fimbriated  processes  of 
the  extremity  of  which  are  supposed  coincidentally  to  grasp 
the  ovary,  while  the  aperture  of  the  tube  is  applied  to  the 
part  corresponding  to  the  matured  and  bursting  vesicle. 

In  animals  whose  capability  of  being  impregnated  occurs  at 
regular  periods,  as  in  the  human  subject,  and  most  Mammalia, 
the  Graafian  vesicles  and  their  contained  ova  appear  to 
arrive  at  maturity,  and  the  latter  to  be  discharged  at  such 
periods  only.  But  in  other  animals,  e.  g.,  the  common  fowl, 
the  formation,  maturation,  and  discharge  of  ova  appear  to 
take  place  almost  constantly. 

It  has  long  been  known,  that  in  the  so-called  oviparous 
animals,  the  separation  of  ova  from  the  ovary  may  take  place 
independently  of  impregnation  by  the  male,  or  even  of  sexual 
union.  And  it  is  now  established  that  a  like  maturation  and 


568          GENERATION    AND    DEVELOPMENT. 

discharge  of  ova,  independently  of  coition,  occurs  in  Mamma- 
lia, the  periods  at  which  the  matured  ova  are  separated  from 
the  ovaries  and  received  into  the  Fallopian  tubes  being  indi- 
cated in  the  lower  Mammalia,  by  the  phenomena  of  heat  or 
rut;  in  the  human  female  by  the  phenomena  of  menstruation. 
Sexual  desire  manifests  itself  in  the  human  female  to  a  greater 
degree  at  these  periods,  and  in  the  female  of  mammiferous 
animals  at  no  other  time.  If  the  union  of  the  sexes  take  place, 
the  ovum  may  be  fecundated,  and  if  no  union  occur  it  perishes. 

That  this  maturation  and  discharge  occur  periodically,  and 
only  during  the  phenomena  of  heat  in  the  lower  Mammalia, 
is  made  probable  by  the  facts  that,  in  all  instances  in  which 
Graafian  vesicles  have  been  found  presenting  the  appearance 
of  recent  rupture,  the  animals  were  at  the  time,  or  had  recently 
been,  in  heat;  that  on  the  other  hand,  there  is  no  authentic 
and  detailed  account  of  Graafian  vesicles  being  found  ruptured 
in  the  intervals  of  the  periods  of  heat;  and  that  female  animals 
do  not  admit  the  males,  and  never  become  impregnated,  ex- 
cept at  those  periods. 

Many  circumstances  make  it  probable  that  the  human 
female  is  subject,  in  these  respects,  to  the  same  law  as  the 
females  of  other  mammiferous  animals ;  namely,  that  in  her 
as  in  them,  ova  are  matured  and  discharged  from  the  ovary 
independent  of  sexual  union,  and  that  this  maturation  and 
discharge  occur  periodically  at  the  epochs  of  menstruation. 
Thus  Graafian  vesicles  recently  ruptured  have  been  frequently 
seen  in  ovaries  of  virgins  or  women  who  could  not  have  been 
recently  impregnated,  and  although  it  is  true  that  the  ova  dis- 
charged under  these  circumstances  have  rarely  been  discovered 
in  the  Fallopian  tube,1  partly  on  account  of  their  minute  size, 
and  partly  because  the  search  has  seldom  been  prosecuted  with 
much  care,  yet  analogy  forbids  us  to  doubt  that  in  the  human 
female,  as  in  the  domestic  quadrupeds,  the  result  and  purpose 
of  the  rupture  of  the  follicles  is  the  discharge  of  the  ova. 

The  evidence  of  the  periodical  discharge  of  ova  at  the  epochs 
of  menstruation  is,  first,  that  nearly  all  authors  who  have 
touched  on  the  point,  agree  that  no  traces  of  follicles  having 
burst  are  ever  seen  in  the  ovaries  before  puberty  or  the  first 
menstruation ;  secondly,  that  in  all  cases  in  which  ovarian 
follicles  have  been  found  burst,  independently  of  sexual  inter- 
course, the  women  were  at  the  time  menstruating,  or  had  very 
recently  passed  through  the  menstrual  state ;  thirdly,  that 
although  conception  is  not  confined  to  the  periods  of  menstru- 

1  See,  however,  the  record  of  two  such  cases  by  Dr.  Letheby,  in  the 
Philosophical  Transactions,  1861. 


MENSTRUATION.  569 

ation,  yet  it  is  more  likely  to  occur  within  a  few  days  after  the 
cessation  of  the  menstrual  flux  than  at  other  times  ;  and,  lastly, 
that  the  ovaries  of  the  human  female  become  turgid  and  vas- 
cular at  the  menstrual  periods,  as  those  of  animals  do  at  the 
time  of  heat. 

From  what  has  been  said,  it  may,  therefore,  be  concluded 
that  the  two  states,  heat  and  menstruation,  are  analogous,  and 
that  the  essential  accompaniment  of  both,  is  the  maturation 
and  extrusion  of  ova.  In  both  there  is  a  state  of  active  con- 
gestion of  the  sexual  organs,  sympathizing  with  the  ovaries  at 
the  time  of  the  highest  degree  of  development  of  the  Graafian 
vesicles;  and,  in  both,  the  crisis  of  this  state  of  congestion  is 
attended  by  a  discharge  of  blood  or  mucus,  or  both,  from  the 
external  organs  of  generation. 

The  occurrence  of  a  menstrual  discharge  is  one  of  the  most 
prominent  indications  of  the  commencement  of  puberty  in  the 
female  sex ;  though  its  absence  even  for  several  years  is  not 
necessarily  attended  with  arrest  of  the  other  characters  of  this 
period  of  life,  or  with  inaptness  for  sexual  union,  or  incapabil- 
ity of  impregnation.  The  average  time  of  its  first  appearance  in 
females  of  this  country  and  others  of  about  the  same  latitude, 
is  from  fourteen  to  fifteen;  but  it  is  much  influenced  by  the 
kind  of  life  to  which  girls  are  subjected,  being  accelerated  by 
habits  of  luxury  and  indolence,  and  retarded  by  contrary 
conditions.  On  the  whole,  its  appearance  is  earlier  in  persons 
dwelling  in  warm  climes  than  in  those  inhabiting  colder  lati- 
tudes; though  the  extensive  investigations  of  Mr.  Roberton 
show  that  the  influence  of  temperature  on  the  development  of 
puberty  has  been  exaggerated.  Much  of  the  influence  attrib- 
uted to  climate  appears  due  to  the  custom  prevalent  in  many 
hot  countries,  as  in  Hindostan,  of  giving  girls  in  marriage  at 
a  very  early  age,  and  inducing  sexual  excitement  previous  to 
the  proper  menstrual  time.  The  menstrual  functions  continue 
through  the  whole  fruitful  period  of  a  woman's  life,  and  usually 
cease  between  the  forty-fifth  and  fiftieth  years. 

The  several  menstrual  periods  usually  occur  at  intervals  of 
a  lunar  month,  the  duration  of  each  being  from  three  to  six 
days.  In  some  women  the  intervals  are  as  short  as  three  weeks 
or  even  less;  while  in  others  they  are  longer  than  a  month. 
The  periodical  return  is  usually  attended  by  pain  in  the  loins, 
a  sense  of  fatigue  in  the  lower  limbs,  and  other  symptoms, 
which  are  different  in  different  individuals.  Menstruation 
does  not  usually  occur  in  pregnant  women,  or  in  those  who 
are  suckling ;  but  instances  of  its  occurrence  in  both  these  con- 
ditions are  by  no  means  rare. 

The  menstrual  discharge  consists  of  blood  effused  from  the 


570          GENERATION    AND    DEVELOPMENT. 

inner  surface  of  the  uterus,  and  mixed  with  mucus  from  the 
uterus,  vagina,  and  external  parts  of  the  generative  apparatus. 
Being  diluted  by  this  admixture,  the  menstrual  blood  coagu- 
lates less  perfectly  than  ordinary  blood ;  and  the  frequent 
acidity  of  the  vaginal  mucus  tends  still  further  to  diminish  its 
coagulability.  This  has  led  to  the  erroneous  supposition  that 
the  menstrual  blood  contains  an  unusually  small  quantity  of 
fibrin,  or  none  at  all.  The  blood-corpuscles  exists  in  it  in  their 
natural  state :  mixed  with  them  may  also  be  found  numerous 
scales  of  epithelium  derived  from  the  mucous  passages  along 
which  the  discharge  flows. 

Corpus  Luteum. 

Immediately  before,  as  well  as  subsequent  to,  the  rupture  of 
a  Graafian  vesicle,  and  the  escape  of  its  ovum,  certain  changes 
ensue  in  the  interior  of  the  vesicle,  which  result  in  the  produc- 
tion of  a  yellowish  mass,  termed  a  corpus  luteum. 

When  fully  formed  the  corpus  luteum  of  mammiferous 
animals  is  a  roundish  solid  body,  of  a  yellowish  or  orange  color, 
and  composed  of  a  number  of  lobules,  which  surround,  some- 
times a  small  cavity,  but  more  frequently  a  small  stelliform 
mass  of  white  substance,  from  which  delicate  processes  pass  as 
septa  between  the  several  lobules.  Very  often,  in  the  cow  and 
sheep,  there  is  no  white  substance  in  the  centre  of  the  corpus 
luteum  ;  and  the  lobules  projecting  from  the  opposite  walls  of 
the  Graafian  vesicle  appear  in  a  section  to  be  separated  by  the 
thinnest  possible  lamina  of  semi-transparent  tissue. 

When  a  Graafian  vesicle  is  about  to  burst  and  expel  the 
ovum,  it  becomes  highly  vascular  and  opaque ;  and,  immedi- 
ately before  the  rupture  takes  place,  its  walls  appear  thickened 
on  the  interior  by  a  reddish  glutinous  or  fleshy-looking  sub- 
stance. Immediately  after  the  rupture,  the  inner  layer  of  the 
wall  of  the  vesicle  appears  pulpy  and  flocculent.  It  is  thrown 
into  wrinkles  by  the  contraction  of  the  outer  layer,  and,  soon, 
red  fleshy  mammillary  processes  grow  from  it,  and  gradually 
enlarge  till  they  nearly  fill  the  vesicle,  and  even  protrude  from 
the  orifice  in  the  external  covering  of  the  ovary.  Subsequently 
this  orifice  closes,  but  the  fleshy  growth  within  still  increases 
during  the  earlier  period  of  pregnancy,  the  color  of  the  sub- 
stance gradually  changing  from  red  to  yellow,  and  its  con- 
sistence becoming  firmer. 

The  corpus  luteum  of  the  human  female  (Fig.  211)  differs 
from  that  of  the  domestic  quadruped  in  being  of  a  firmer  tex- 
ture, and  having  more  frequently  a  persistent  cavity  at  its 
centre,  and  in  the  stelliform  cicatrix,  which  remains  in  the 


CORPUS    LUTEUM. 


571 


cases  where  the  cavity  is  obliterated,  being  proportionately  of 
much  larger  bulk.  The  quantity  of  yellow  substance  formed 
is  also  much  less  :  and,  although  the  deposit  increases  after  the 
vesicle  has  burst,  yet  it  does  not  usually  form  mammillary 
growths  projecting  into  the  cavity  of  the  vesicle,  and  never 
protrudes  from  the  orifice,  as  is  the  case  in  other  Mammalia. 
It  maintains  the  character  of  a  uniform,  or  nearly  uniform, 
layer,  which  is  thrown  into  wrinkles,  In  consequence  of  the 
contraction  of  the  external  tunic  of  the  vesicle.  After  the 
orifice  of  the  vesicle  has  closed,  the  growth  of  the  yellow  sub- 
stance continues  during  the  first  half  of  pregnancy,  till  the 
cavity  is  reduced  to  a  comparatively  small  size,  or  is  obliterated ; 
in  the  latter  case,  nearly  a  white  stelliform  cicatrix  remains  in 
the  centre  of  the  corpus  luteum. 


A 


Corpora  lutea  of  different  periods.  B.  Corpus  luteum  of  about  the  sixth  week  after 
impregnation,  showing  its  plicated  form  at  that  period.  1.  Substance  of  the  ovary. 
'2.  Substance  of  the  corpus  luteum.  3.  A  grayish  coagulum  in  its  cavity.  After  Dr. 
Paterson.  A.  Corpus  luteum,  two  days  after  delivery.  D.  In  the  twelfth  week  after 
delivery.  After  Dr.  Montgomery. 

An  effusion  of  blood  generally  takes  place  into  the  cavity  of 
the  Graah'an  vesicle  at  the  time  of  its  rupture,  especially  in 
the  human  subject ;  but  it  has  no  share  in  forming  the  yellow 
body;  it  gradually  loses  its  coloring  matter,  and  acquires  the 
character  of  a  mass  of  fibrin.  The  serum  of  the  blood  some- 
times remains  included  within  a  cavity  in  the  centre  of  the 
coagulum,  and  then  the  decolorized  fibrin  forms  a  membrani- 
form  sac,  lining  the  corpus  luteum.  At  other  times  the  serum 
is  removed,  and  the  fibrin  constitutes  a  solid  stelliform  mass. 

The  yellow  substance  of  which  the  corpus  luteum  consists, 
both  in  the  human  subject  and  in  the  domestic  animals,  is  a 
growth  from  the  inner  surface  of  the  Graafian  vesicle,  the  re- 
sult of  an  increased  development  of  the  cells  forming  the  mem- 


572 


GENERATION  AND  DEVELOPMENT. 


brana  granulosa,  which  naturally  Hues  the  internal  tunic  of 
the  vesicle. 

The  first  changes  of  the  internal  coat  of  the  Graafian  vesicle 
in  the  process  of  formation  of  a  corpus  luteura,  seem  to  occur 
in  every  case  in  which  an  ovum  escapes ;  as  well  in  the  human 
subject  as  in  the  domestic  quadrupeds.  If  the  ovum  is  im- 
pregnated, the  growth  of  the  yellow  substance  grows  on  during 
nearly  the  whole  period  of  gestation,  and  forms  the  large  cor- 
pus luteum  commonly  described  as  a  characteristic  mark  of 
impregnation.  If  the  ovum  is  not  impregnated,  the  growth  of 
yellow  substance  on  the  internal  surface  of  the  vesicle  proceeds, 
in  the  human  ovary,  no  further  than  the  formation  of  a  thin 
layer,  which  shortly  disappears ;  but  in  the  domestic  animals 
it  continues  for  some  time  after  the  ovum  has  perished,  and 
forms  a  corpus  luteum  of  considerable  size.  The  fact,  that  a 
structure,  in  its  essential  characters  similar  to,  though  smaller 
than,  a  corpus  luteum  observed  during  pregnancy,  is  formed 
in  the  human  subject,  independent  of  impregnation  or  of  sexual 
union,  coupled  with  the  varieties  in  size  of  corpora  lutea  formed 
during  pregnancy,  necessarily  renders  unsafe  all  evidence  of 
previous  impregnation  founded  on  the  existence  of  a  corpus 
luteum  in  the  ovary. 

The  following  table  by  Daltou,  expresses  well  the  differences 
between  the  corpus  luteum  of  the  pregnant  and  uuimpregnated 
condition  respectively. 


At  the  end  of 
three  weeks, 
Gne  month, 


Two  months, 
Six  months, 
Nine  months, 


CORPUS  LUTEUM  OF  MEN- 
STRUATION. 

Three-quarters  of  an   inch 

reddish  ;  convoluted  wall 
Smaller;  convoluted  wall 

bright  yellow;  clot  still 

reddish. 
Reduced  to  the  condition 

of  an  insignificant  cica- 

trix. 

Absent. 


Absent. 


CORPUS  LUTEUM  OP  PREG- 
NANCY. 

in  diameter;  central  clot 

pale. 

Larger;  convoluted  wall 
bright  yollow  ;  clot  still 
reddish. 

Seven-eighths  of  an  inch 
in  diameter;  convoluted 
wall  bright  yellow  ;  clot 
perfectly  decolorized. 

Still  as  large  as  at  end  of 
second  mouth  ;  clot  fib- 
rinous;  convoluted  wall 
paler. 

One-half  an  inch  in  diam- 
eter ;  central  clot  con- 
verted into  a  radiating 
cicatrix  ;  the  external 
wall  tolerably  thick  and 
convoluted,  but  without 
anj7  bright  yellow  color. 


IMPREGNATION    OF    THE    OVUM.  573 

IMPREGNATION    OF    THE   OVUM. 

Male  Sexual  Functions. 

The  fluid  of  the  male,  by  which  the  ovum  is  impregnated, 
consists  essentially  of  the  semen  secreted  by  the  testicles  ;  and 
to  this  are  added,  as  necessary,  perhaps,  to  its  perfection,  a 
material  secreted  by  the  vesiculae  serainales,  in  which,  as  in 
reservoirs,  the  semen  lies  before  its  discharge,  as  well  as  the 
secretion  of  the  prostate  gland,  and  of  Cowper's  glands.  Por- 
tions of  these  several  fluids  are,  probably,  all  discharged,  to- 
gether with  the  proper  secretion  of  the  testicles. 

The  secreting  structure  of  the  testicle  is  disposed  in  two 
contiguous  parts  (1),  the  body  of  the  testicle  inclosed  within 
a  tough  fibrous  membrane,  the  tunica  albuginea,  on  the  outer 
surface  of  which  is  the  serous  covering  formed  by  the  tunica 
vaginalis,  and  (2)  the  epididymw.  The  vas  deferens,  the  main 
trunk  of  the  secreting  tube,  when  followed  back  to  its  origin, 
is  found  to  pass  to  the  lower  part  of  the  epididymis,  and  as- 
sumes there  a  much  less  diameter  with  a  very  tortuous  course ; 
with  its  various  convolutions  it  forms  first  the  mass  named 
globus  minor,  then  the  body,  and  then  the  globus  major  of  the 
epididymis.  At  the  last-named  part,  the 
duct  divides  into  ten  or  twelve  small 
branches,  the  convolutions  of  which  form 
coniform  masses,  named  coni  vasculosi ; 
and  the  vessels  con  tinned  from  these,  the 
vasa  efferentia,  after  anastomosing,  one 
with  another,  in  what  is  called  the  rete 
testis,  lead  finally  through  the  tubuli  recti 
or  vasa  recta  to  the  tubules  which  form 
the  proper  substance  of  the  testicle, 
wherein  they  are  arranged  in  lobules, 
closely  packed,  and  all  attached  to  the 
tough  fibrous  tissue  at  the  back  of  the 
testicle. 

The  seminal  tubes,  or  tubuli  seminiferi, 
which  compose  the  proper  substance  of 
the  testicle,  are  fine  thread-like  tubules, 
formed  of  simple  homogeneous  membrane,  measuring  on  an 
average  TiTth  to  ^^h  of  an  inch  in  diameter,  and  lined  with 
epithelium  or  gland-C3lls.  Rarely  branching,  they  extend  as 
simple  tubes  through  a  great  length,  with  the  same  uniform 
structure,  and  probably  terminate  either  in  free  closed  extremi- 
ties or  in  loops.  Their  walls  are  covered  with  fine  capillary 
bloodvessels,  through  which,  reckoning  their  great  extent  in 


574          GENERATION    AND    DEVELOPMENT. 

comparison  with  the  size  of  the  spermatic  artery,  the  blood 
must  move  very  slowly. 

The  seminal  fluid  secreted  by  the  testicle  is  one  of  those  se- 
cretions in  which  a  process  of  development  is  continued  after 
its  formation  by  the  secreting  cells,  and  its  discharge  from  them 
into  the  tubes.  The  principal  part  of  this  development  con- 
sists in  the  formation  of  the  peculiar  bodies  named  seminal  fila- 
ments, spermatozoa  or  spermatozoids  (Fig.  213),  the  complete 
development  of  which,  in  their  full  proportion  of  number,  is 
not  achieved  till  the  semen  has  reached,  or  has  for  some  time 
lain  in,  the  vesiculse  seminales.  Earlier,  after  its  first  secretion, 
the  semen  contains  none  of  these  bodies,  but  granules  and 
round  corpuscles  (seminal  corpuscles),  like  large  nuclei,  in- 
closed within  parent-cells  (Fig.  213).  Within  reach  of  these 
corpuscles,  or  nuclei,  a  seminal  filament  is  developed,  by  a 
similar  process  in  nearly  all  animals.  Each  corpuscle,  or  nu- 
cleus, is  filled  with  granular  matter ;  this  is  gradually  con- 
verted into  a  spermatozoid,  which  is  at  first  coiled  up,  and  in 
contact  with  the  inner  surface  of  the  wall  of  the  corpuscle 
CFig.  213,  C,  1). 

Thus  developed,  the  human  seminal  filaments  consist  of  a 
long,  slender,  tapering  portion,  called  the  body  or  tail,  to  dis- 
tinguish it  from  the  head,  an  oval  or  pyriform  portion  of  larger 
diameter,  flattened,  and  sometimes  pointed.  They  are  from 
5- j-0th  to  gj^th  of  an  inch  in  length,  the  length  of  the  head 
alone  being  from  70Vi)ta  to  ^oVotn  °f  an  incn>  an(*  its  width 
about  half  as  much.  They  present  no  trace  of  structure,  or 
dissimilar  organs ;  a  dark  spot  often  observed  in  the  head,  is 
probably  due  to  its  being  concave,  like  a  blood-corpuscle. 
They  move  about  in  the  fluid  like  so  many  minute  corpuscles, 
with  each  a  ciliary  process,  lashing  their  tails,  and  propelling 
their  heads  forwards  in  various  lines.  Their  movement,  which 
is  probably  essentially,  as  well  as  apparently,  similar  to  that 
of  ciliary  processes,  appears  nearly  independent  of  external 
conditions,  provided  the  natural  density  of  the  fluid  is  pre- 
served ;  disturbing  this  condition,  by  either  evaporating  the 
semen  or  diluting  it,  will  stop  the  movement.  It  may  continue 
within  the  body  of  the  female  for  seven  or  eight  days,  and  out 
of  the  body  for  at  least  nearly  twenty-four  hours.  The  direc- 
tion of  the  movement  is  quite  uncertain ;  but  in  general,  the 
current  that  each  excites  keeps  it  from  the  contact  of  others. 
The  rate  of  motion,  according  to  Valentin,  is  about  one  inch 
in  thirteen  minutes. 

Respecting  the  purpose  served  by  these  seminal  filaments, 
or  concerning  their  exact  nature,  little  that  is  certain  can  be 
said.  Their  occurrence  in  the  impregnating  fluid  of  nearly  all 


SEMINAL    FILAMENTS. 


575 


classes  of  animals,  proves  that  they  are  essential  to  the  process 
of  impregnation ;  but  beyond  this,  and  that  their  contact  with 
the  ovum  is  necessary  for  its  development,  nothing  is  known. 


A,  spermatic  filaments  from  the  human 
vas  deferens  (from  Kolliker).  1,  magnified 
850  diameters ;  2,  magnified  800  diameters  ; 
a,  from  the  side ;  6,  from  above.  B,  sper- 
matic cells  and  spermatozoa  of  the  bull 
undergoing  development  (from  Kolliker) 
15.0..  i(  spermatic  cells,  with  one  or  two 
nuclei,  one  of  them  clear;  2,  3,  free  nuclei, 
with  spermatic  filaments  forming;  4,  the 
filaments  elongated  and  the  body  widened  ; 
5,  filaments  nearly  fully  developed.  C,  es- 
cape of  the  spermatozoa  from  their  cells  in 
the  same  animal.  1,  spermatic  cell  contain- 
ing the  spermatozoon  coiled  up  within  it; 
2,  the  cells  elongated  by  the  partial  uncoil- 
ing of  the  spermatic  filament ;  3,  a  cell  from 
which  the  filament  has  in  part  become  free  ; 
4,  the  same  with  the  body  also  partially 
free  ;  5,  spermatozoon  from  the  epididymis 
with  vestiges  of  the  cell  adherent;  6,  sper- 
matozoon from  the  vas  deferens,  showing 
the  small  enlargement,  b,  on  the  filament. 


The  seminal  fluid  is,  probably,  after  the  period  o£  puberty, 
secreted  constantly,  though,  except  under  excitement,  very 
slowly,  in  the  tubules  of  the  testicles.  From  these  it  passes 


576          GENERATION    AND    DEVELOPMENT. 

along  the  vasa  deferentia  into  the  vesiculse  seminales,  whence, 
if  not  expelled  in  emission,  it  may  be  discharged,  as  slowly  as 
it  enters  them,  either  with  the  urine,  which  may  remove  mi- 
nute quantities,  mingled  with  the  mucus  of  the  bladder  and 
the  secretion  of  the  prostate,  or  from  the  urethra  in  the  act  of 
defecation. 

The  vcsiculce  seminales  have  the  appearance  of  outgrowths 
from  the  vasa  deferentia.  Each  vas  deferens,  just  before  it 
enters  the  prostate  gland,  through  part  of  which  it  passes  to 
terminate  in  the  urethra,  gives  off  a  side-branch,  which  bends 
back  from  it  at  an  acute  angle;  and  this  branch  dilating, 
variously  branching,  and  pursuing  in  both  itself  and  its 
branches  a  tortuous  course,  constructs  the  vesicula  serninalis. 
Each  of  the  vesiculse,  therefore,  might  be  unravelled  into  a 
single  branching  tube,  sacculated,  convoluted,  and  folded  up. 

The  mucous  membrane  lining  the  vesiculse  seminales,  like 
that  of  the  gall-bladder,  is-  minutely  wrinkled  and  set  with 
folds  and  ridges  arranged  so  as  to  give  it  a  finely  reticulated 
appearance.  The  rest  of  their  walls  is  formed,  chiefly  of  a 

FIG.  214. 


The  base  of  the  male  bladder,  with  the  .vesiculae  semiuales  and  prostate  gland. 
1.  The  urinary  bladder.  2.  The  longitudinal  layer  of  muscular  fibres.  3.  The  pro- 
state gland.  4  Membranous  portion  of  the  urethra.  5.  The  ureters.  6.  Bloodves- 
sels. 7.  Left;  8.  Right  vas  deferens.  9.  Left  seminal  vesicle  in  its  natural  posi- 
tion. 10.  Dnctus  ejaculatorius  of  the  left  side  traversing  the  prostate  gl  and.  11. 
Right  seminal  vesicle  injected  and  unravelled.  12,  13.  Blind  pouches  of  vesiculse. 
14  Right  ductus  ejaculatorius  traversing  the  prostate.— (Haller.) 

layer  of  organic  muscular  fibres,  from  which  they  derive  con- 
tractile power  for  the  expulsion  of  their  contents. 

To  the  vesiculse  seminales  a  double  function  may  be  as- 
signed ;  for  they  both  secrete  some  fluid  to  be  added  to  that  of 


THE    VESICUL^:    SEMINALES.  577 

the  testicles,  and  serve  as  reservoirs  for  the  seminal  fluid.  The 
former  is  their  most  constant  and  probably  most  important 
office ;  for  in  the  horse,  bear,  guinea-pig,  and  several  other 
animals,  in  whom  the  vesiculse  seminales  are  large  and  of  ap- 
parently active  function,  they  do  not  communicate  with  the 
vasa  deferentia,  but  pour  their  secretions,  separately,  though 
it  may  be  simultaneously,  into  the  urethra.  In  man,  also, 
when  one  testicle  is  lost,  the  corresponding  vesicula  seminalis 
suffers  no  atrophy,  though  its  function  as  a  reservoir  is  abro- 
gated. But  how  the  vesiculse  seminales  act  as  secreting  or- 
gans is  unknown  ;  the  peculiar  brownish  fluid  which  they  con- 
tain after  death  does  not  properly  represent  their  secretion,  for 
it  is  different  in  appearance  from  anything  discharged  during 
life,  and  is  mixed  with  semen.  It  is  nearly  certain,  however, 
that  their  secretion  contributes  to  the  proper  composition  of 
the  impregnating  fluid  ;  for  in  all  the  animals  in  whom  they 
exist,  and  in  whom  the  generative  functions  are  exercised  at 
only  one  season  of  the  year,  the  vesiculse  seminales,  whether 
they  communicate  with  the  vasa  deferentia  or  not,  enlarge 
commensurately  with  the  testicles  at  the  approach  of  that 
season. 

That  the  vesiculse  are  also  reservoirs  in  which  the  seminal 
fluid  may  lie  for  a  time  previous  to  its  discharge,  is  shown  by 
their  commonly  containing  the  seminal  filaments  in  larger 
abundance  than  any  portion  of  the  seminal  ducts  themselves 
do.  The  fluid-like  mucus,  also,  which  is  often  discharged  from 
the  vesiculse  in  straining  during  defecation,  commonly  contains 
seminal  filaments.  But  no  reason  can  be  given  why  this  office 
of  the  vesiculse  should  not  be  equally  necessary  to  all  the 
animals  whose  testicles  are  organized  like  those  of  man,  or 
why  in  many  animals  the  vesiculse  are  wholly  absent. 

There  is  an  equally  complete  want  of  information  respecting 
the  secretions  of  the  prostate  and  Cowper's  glands,  their  nature 
and  purposes.  That  they  contribute  to  the  right  composition 
of  the  impregnating  fluid,  is  shown  both  by  the  position  of  the 
glands  and  by  their  enlarging  with  the  testicles  at  the  ap- 
proach of  an  animal's  breeding-time.  But  that  they  contribute 
only  a  subordinate  part  is  shown  by  the  fact,  that,  when  the 
testicles  are  lost,  though  these  other  organs  be  perfect,  all 
procreative  power  ceases. 

The  mingled  secretions  of  all  the  organs  just  described, 
form  the  semen  or  seminal  fluid.  Its  corpuscles  have  been 
already  described  (p.  574) ;  its  fluid  part  has  not  been  satis- 
factorily analyzed;  but  Henle  says  it  contains  fibrin,  because, 
shortly  after  being  discharged,  flocculi  form  in  it  by  sponta- 


578          GENERATION     AND     DEVELOPMENT. 

neous  coagulation,  and  leave  the  rest  of  it  thinner  and  more 
liquid,  so  that  the  filaments  move  in  it  more  actively. 

Nothing  has  shown  what  it  is  that  makes  this  fluid  with  its 
corpuscles  capable  of  impregnating  the  ovum,  or  (what  is  yet 
more  remarkable)  of  giving  to  the  developing  offspring  all  the 
characters,  in  features,  size,  mental  disposition,  and  liability 
to  disease,  which  belong  to  the  father.  This  is  a  fact  wholly  in- 
explicable ;  and  is,  perhaps,  only  exceeded  in  strangeness  by 
those  facts  which  show  that  the  seminal  fluid  may  exert  such 
an  influence,  not  only  on  the  ovum  which  it  impregnates,  but, 
through  the  medium  of  the  mother,  on  many  which  are  sub- 
sequently impregnated  by  the  seminal  fluid  of  another  male. 
It  has  been  often  observed,  for  example,  that  a  well-bred  bitch, 
if  she  have  been  once  impregnated  by  a  mongrel  dog,  will  not 
bear  thorough-bred  puppies  in  the  next  two  or  three  litters 
after  that  succeeding  the  copulation  with  the  mongrel.  But 
the  best  instance  of  the  kind  was  in  the  case  of  a  mare  belong- 
ing to  Lord  Morton,  who,  while  he  was  in  India,  wished  to 
obtain  a  cross-breed  between  the  horse  and  quagga,  and  caused 
this  mare  to  be  covered  by  a  male  quagga.  The  foal  that  she 
next  bore  had  distinct  marks  of  the  quagga,  in  the  shape  of 
its  head,  black  bars  on  the  legs  and  shoulders,  and  other  char- 
acters. After  this  time  she  was  thrice  covered  by  horses,  and 
every  time  the  foal  she  bore  had  still  distinct,  though  decreas- 
ing marks  of  the  quagga ;  the  peculiar  characters  of  the  quagga 
being  thus  impressed  not  only  on  the  ovum  then  impregnated, 
but  on  the  three  following  ova  impregnated  by  horses.  It 
would  appear,  therefore,  that  the  constitution  of  an  impreg- 
nated female  may  become  so  altered  and  tainted  with  the 
peculiarities  of  the  impregnating  male,  through  the  medium 
of  the  foetus,  that  she  necessarily  imparts  such  peculiarities  to 
any  offspring  she  may  subsequently  bear  by  other  males.  Of 
the  direct  means  by  which  a  peculiarity  of  structure  on  the 
part  of  a  male  is  thus  transmitted,  nothing  whatever  is  known. 

DEVELOPMENT. 

Changes  in  the  Ovum  previous  to  the  Formation  of  the  Embryo. 

Of  the  changes  which  the  ovum  undergoes  previous  to  the 
formation  of  the  embryo,  some  occur  while  it  is  still  in  the 
ovary,  and  are  apparently  independent  of  impregnation  : 
others  take  place  after  it  has  reached  the  Fallopian  tube.  The 
knowledge  we  possess  of  these  changes  is  derived  almost  ex- 
clusively from  observations  on  the  ova  of  mammiferous  ani- 


CLEAVAGE    OF    THE     YELK.  579 

mals,  especially  the  bitch  and  rabbit :  but  it  may  be  inferred 
that  analogous  changes  ensue  in  the  human  ovum. 

Bischoff  describes  the  yelk  of  an  ovarian  ovum  after  coitus 
as  being  unchanged  in  its  characters,  with  the  single  exception 
of  being  fuller  and  more  dense ;  it  is  still  granular,  as  before, 
and  does  not  possess  any  of  the  cells  subsequently  found  in  it. 
The  germinal  vesicle  always  disappears,  sometimes  before  the 
ovum  leaves  the  ovary,  at  other  times  not  until  it  has  entered 
the  Fallopian  tube ;  but  always  before  the  commencement  of 
the  metamorphosis  of  the  yelk. 

As  the  ovum  approaches  the  middle  of  the  Fallopian  tube,  it 
begins  to  receive  a  new  investment,  consisting  of  a  layer  of 
transparent  albuminous  or  glutinous  substance,  which  forms 
upon  the  exterior  of  the  zona  pellucida.  It  is  at  first  exceed- 
ingly fine,  and,  owing  to  this,  and  to  its  transparency,  is  not 
easily  recognized  :  but  at  the  lower  part  of  the  Fallopian  tube 
it  acquires  considerable  thickness. 

About  this  time,  that  is  to  say,  during  its  passage  through 
the  Fallopian  tube,  a  very  remarkable  change  takes  place  in 
the  interior  of  the  ovum.  The  whole  yelk  becomes  constricted 
in  the  middle,  and  surrounded  by  a  furrow,  which,  gradually 
deepening,  at  length  cuts  the  yelk  in  half,  while  the  same 
process  begins  almost  immediately  in  each  half  of  the  yelk, 
and  cuts  it  also  in  two.  The  same  process  is  repeated  in  each 
of  the  quarters,  and  so  on,  until  at  last  by  continual  cleavings 
the  whole  yelk  is  changed  into  a  mulberry-like  mass  of  small 
and  more  or  less  rounded  bodies,  sometimes  called  "vitelline 
spheres,"  the  whole  still  inclosed  by  the  zona  pellucida  or  vitel- 
line membrane  (Fig.  215).  Each  of  these  little  spherules  con- 
tains a  transparent  vesicle,  like  an  oil-globule,  which  is  seen 
with  difficulty,  on  account  of  its  being  enveloped  by  the  yelk- 
granules  which  adhere  closely  to  its  surface. 

The  cause  of  this  singular  subdivision  of  the  yelk  is  quite 
obscure :  though  the  immediate  agent  in  its  production  seems 
so  be  the  central  vesicle  contained  in  each  division  of  the  yelk. 
Originally  there  was  probably  but  one  vesicle,  situated  in  the 
centre  of  the  entire  granular  mass  of  the  yelk,  and  probably 
derived  from  the  germinal  vesicle.  This,  by  some  process  of 
multiplication,  divides  and  subdivides  :  then  each  division  and 
subdivision  attracts  around  itself,  as  a  centre,  a  certain  portion 
of  the  substance  of  the  yelk. 

About  the  time  at  which  the  manimiferous  ovum  reaches 
the  uterus,  the  process  of  division  and  subdivision  of  the  yelk 
appears  to  have  ceased,  its  substance  having  been  resolved 
into  its  ultimate  and  smallest  divisions,  while  its  surface  pre- 


580 


GENERATION  AND  DEVELOPMENT. 


FIG.  215. 


sents  a  imiform  finely-granular  aspect,  instead  of  its  late  mul- 
berry-like appearance.      The  ovum,  indeed,  appears  at  fii\<t 

sight  to  have  lost  all  trace  of 
the  cleaving  process, and,  with 
the  exception  of  being  paler 
and  more  translucent,  almost 
exactly  resembles  the  ovarian 
ovum,  its  yelk  consisting  ap- 
parently of  a  confused  mass 
of  finely  granular  substance. 
But  on  a  more  careful  exam- 
ination, it  is  found  that  these 
granules  are  aggregated  into 
numerous  minute  spherical 
masses,  each  of  which  contains 
a  clear  vesicle  in  its  centre, 
but  is  not,  at  this  period,  pro- 
vided with  an  enveloping  mem- 
brane, and  possesses  none  of 
the  other  characters  of  a  cell. 
The  zona  pellucida,  and  the 
layer  of  albuminous  matter 
surrounding  it,  have  at  this 
time  the  same  character  as 
when  at  the  lower  part  of  the 
Fallopian  tube. 

The  time  occupied  in  the 
passage  of  the  ovum,  from  the 
ovary  to  the  uterus,  occupies 
probably  eight  or  ten  days  in 
the  human  female. 

Shortly  after  this,  important 
changes  ensue.  Each  of  the 
several  globular  segments  of 
the  yelk  becomes  surrounded 
by  a  membrane,  and  is  thus 
converted  into  a  cell,  the 
nucleus  of  which  is  formed  by 
the  central  vesicle,  the  con- 
tents by  the  granular  matter 
originally  composing  the  glob- 
ule: these  granules  usually 
arrange  themselves  concen- 
trically around  the  nucleus. 

Diagrams  of  the  various  stages  of  cleav-       When     the     peripheral     Cells, 

age  of  the  yelk  (after  Daiton).  which    are  formed    first,  are 


CHANGES    OF    THE    OVUM.  581 

fully  developed,  they  arrange  themselves  at  the  surface  of 
the  yelk  into  a  kind  of  membrane,  and  at  the  same  time  as- 
sume a  pentagonal  or  hexagonal  shape  from  mutual  pressure, 
so  as  to  resemble  pavement-epithelium.  As  the  globular 
masses  of  the  interior  are  gradually  converted  into  cells,  they 
also  pass  to  the  surface  and  accumulate  there,  thus  increasing 
the  thickness  of  the  membrane  already  formed  by  the  more 
superficial  layer  of  cells,  while  the  central  part  of  the  yelk  re- 
mains filled  only  with  a  clear  fluid.  By  this  means  the  yelk 
is  shortly  converted  into  a  kind  of  secondary  vesicle,  the  walls 
of  which  are  composed  externally  of  the  original  vitelline 
membrane,  and  within  by  the  newly  formed  cellular  layer, 
the  blastodermic  or  germinal  membrane,  as  it  is  called.  Very 
soon,  however,  the  latter,  by  the  development  of  new  cells,  in- 
creases in  thickness,  and  splits  into  two  layers,  so  that  now 
the  ovum  has  three  coats.  The  vitelline  membrane  on  the 
outside,  and,  within  this,  the  outer  and  the  inner  layers  of  the 
blastodermic  membrane. 

Of  the  last-named  layers,  the  superior  or  outer,  which  lies 
next  to  the  zona  pellucida  or  vitelline  membrane,  is  called  the 
serous  layer ;  from  it  are  developed  the  organs  of  the  animal 
system  of  the  body,  e.  g.,  the  bones,  muscles,  and  integuments. 
The  inferior  or  inner  layer,  in  contact  with  the  yelk  itself,  is 
named  the  mucous  layer,  and  serves  for  the  formation  of  the 
internal  or  visceral  system  of  organs. 

Changes  of  the  Ovum  within  the  Uterus. 

Very  soon  after  its  formation,  and  division  into  two  layers, 
the  blastodermic  vesicle  or  membrane  presents  at  one  point 
on  its  surface  an  opaque  roundish  spot,  which  is  produced  by 
an  accumulation  of  cells  and  nuclei  of  cells,  of  less  transpar- 
ency than  elsewhere.  This  space,  the  "  area  germinativa  " 
or  germinal  area,  is  the  part  at  which  the  embryo  first  ap- 
pears. 

At  first  the  area  germinativa  has  a  rounded  form,  but  it 
soon  loses  this  and  becomes  oval,  then  pear-shaped,  and  while 
this  change  in  form  is  taking  place,  there  gradually  appears 
in  its  centre  a  clear  space  or  area  pellucida  (Fig.  216),  bounded 
externally  by  a  more  opaque  circle,  the  obscurity  being  due 
to  the  greater  accumulation  of  nucleated  cells  and  nuclei  at 
that  part  than  in  the  area  pellucida. 

The  first  trace  of  the  embryo  in  the  centre  of  the  area  pellu- 
cida consists  of  a  shallow  groove  or  channel,  the  primitive 
groove  (Fig.  216),  formed  of  the  external  or  serous  fold  of  the 

49 


582 


GENERATION  AND  DEVELOPMENT. 


FIG. 216. 


(After  Dalton.)  Impregnated  egg, 
with  commencement  of  formation  of 
ombryo  ;  showing  the  area  germina- 
tiva  or  embryonic  spot,  the  area  pel- 
lucida,  and  the  primitive  groove  or 
trace. 


germinal  membrane,  the  groove  being  wider  at  its  anterior  or 

cephalic  extremity,  and  taper- 
ing towards  the  opposite  ex- 
tremity. 

Coincidently  with  the  forma- 
tion of  the  primitive  groove,  two 
oval  masses  of  cells,  the  lamincK 
dorsales,  appear,  one  on  each 
side  of  the  groove.  At  first 
scarcely  elevated  above  the 
plane  of  the  germinal  mem- 
brane, they  soon  rise  into  two 
prominent  masses,  the  upper 
borders  of  which  gradually  tend 
towards  each  other,  turning  in- 
wards over  the  primitive  groove. 
The  parts  from  opposite  sides 
then  unite,  and  convert  the 
primitive  groove  into  a  <tube, 
large  and  rounded  in  front,  nar- 
row and  lancet-shaped  behind,  which  is  the  central  canal  of 
the  cerebro-spinal  axis,  and  contains  the  rudimental  spinal 
cord  and  brain,  which  are  developed  in  its  interior  (Fig.  217). 
Immediately  beneath,  and  in  a  line  parallel  with  the  primi- 
tive groove,  may  be  seen,  about  the  same  time,  a  narrow  linear 
mass  of  cells,  the  chorda  dorsalis,  which  forms  the  basis  around 
which  the  bodies  of  the  vertebrae  are  developed.  The  devel- 
opment of  this  column  is  early  indicated  by  the  appearance 
of  a  few  square,  at  first  indistinct,  plates,  the  rudiments  of 
vertebrae  (Fig.  217,  D),  which  begin  to  appear  at  about  the 
middle  of  each  dorsal  lamina. 

While  the  dorsal  laminae  are  closing  over  the  primitive 
groove,  thickened  prolongations  of  the  same  serous  layer  are 
given  off  from  the  lower  margin  of  each  of  them,  and  are 
named  lamince  viscerales  sen  ventrales.  These  visceral  laminae 
by  degrees  bend  downwards  and  inwards,  and  at  length,  in- 
closing a  part  of  the  yelk,  unite  and  form  the  anterior  walls 
of  the  trunk — inclosing  the  abdominal  cavity  below,  as  the 
dorsal  plates  inclose  the  cerebro-spinal  canal  above. 


Umbilical  Vesicle. 

The  ventral  laminae,  as  they  extend  downwards  and  inwards, 
at  first  proceed  on  the  same  plane  with  the  inner  layer  of 
the  germinal  membrane,  which  immediately  lines  them.  Soon, 
however,  they  show  a  tendency  to  turn  inwards,  so  as  to  con- 


THE    UMBILICAL    VESICLE. 


583 


strict  the  yelk,  and  inclose  only  a  part  of  it ;  and  soon  after- 
wards the  yelk  and  the  inner  layer  of  the  germinal  membrane 


FIG.  217. 


Portion  of  the  germinal  membrane,  with  rudiments  of  the  embryo;  from  the 
ovum  of  a  bitch.  The  primitive  groove,  A,  is  not  yet  closed,  and  at  its  upper  or 
cephalic  end  presents  three  dilatations  B,  which  correspond  to  the  three  divisions  or 
vesicles  of  the  brain.  At  its  lower  extremity  the  groove  presents  a  lancet-shaped 
dilatation  (sinus  rhomboidalis)  c.  The  margins  of  the  groove  consist  of  clear  pel- 
lucid nerve  substance.  Along  the  bottom  of  the  groove  is  observed  a  faint  streak, 
which  is  probably  the  chorda  dorsalis.  D.  Vertebral  plates.  After  Bischoff. 


FIG.  218. 


Diagram  showing  vascular  area  in  the  chick,    a.  Area  pellucida.    6.  Area 
vasculosa.    c.  Area  vitellina. 


584 


GENERATION  AND  DEVELOPMENT. 


that  contains  it,  are  separated  into  two  portions,  one  of  which 
is  retained  within  the  body  of  the  embryo,  while  the  other  re- 
mains outside,  and  receives  the  name  of  the  umbilical  vesicle 
(v,  Fig.  219).  The  cavity  of  the  latter  communicates  for  some 
time  with  that  of  the  abdomen,  through  what  is  called  the 
umbilicus,  by  means  of  a  gradually  narrowing  canal,  called 
the  vitelline  duct;  the  interior  of  the  abdomen  and  that  of  the 


Diagrammatic  section  showing  the  relation  in  a  mammal  and  in  man  between  the 
primitive  alimentary  canal  and  the  membranes  of  the  ovum.  The  stage  represented 
in  this  diagram  corresponds  to  that  of  the  fifteenth  or  seventeenth  day  in  the  human 
embryo,  previous  to  the  expansion  of  the  allantois :  c,  the  villous  chorion ;  a,  the 
amnion ;  a',  the  place  of  convergence  of  the  amnion  and  reflection  of  the  false  am- 
nion  a"  a",  or  outer  or  corneous  layer;  e,  the  head  and  trunk  of  the  embryo,  com- 
prising the  primitive  vertebrae  and  cerebro^spinal  axis ;  i,  i,  the  simple  alimentary 
canal  in  its  upper  and  lower  portions;  v,  the  yelk-sac  or  umbilical  vesicle  ;  v  i,  the 
vitello- intestinal  opening;  u,  the  allantois  connected  by  a  pedicle  with  the  anal  por- 
tion of  the  alimentary  canal. 


umbilical  vesicle  being  lined  by  a  continuous  layer  of  the 
inner  stratum,  or  mucous  layer  of  the  germinal  membrane ; 
while  around  both  of  them  is  a  continuation  of  the  outer,  or 
serous  layer  (Fig.  219).  From  that  portion  of  the  mucous  layer 


THE    AM  N  ION    AND    ALLANTOIS.  585 

which  is  now  inclosed  within  the  body  of  the  embryo,  the  in- 
testinal canal  is  developed. 

Thus  by  the  constriction  which  the  fold  of  germinal  mem- 
brane, in  which  the  abdominal  walls  are  formed,  produces  at 
the  umbilicus,  the  body  of  the  embryo  becomes  in  great  meas- 
ure detached  from  the  yelk-sac  or  umbilical  vesicle,  though 
the  cavity  of  the  rudimentary  intestine  still  communicates  with 
it  through  the  vitelline  or  omphalo-mesenteric  duct,  and  con- 
tains part  of  the  yelk-substance  with  which  the  vesicle  was 
filled.  The  yelk-sac  contains,  however,  the  greater  part  of  the 
substance  of  the  yelk,  and  furnishes  a  source  whence  nutriment 
is  derived  for  the  embryo.  In  birds,  the  contents  of  the  yelk- 
sac  afford  nourishment  until  the  end  of  incubation :  but  in 
Mammalia,  the  office  of  the  corresponding  umbilical  vesicle 
ceases  at  a  very  early  period,  the  quan- 
tity of  yeik  is  small,  and  the  embryo  FIG.  2-20. 
soon  becomes  independent  of  it  by  the 
connections  it  forms  with  the  parent. 
Moreover,  in  birds,  as  the  sac  is  emptied, 
it  is  gradually  drawn  into  the  abdomen 
through  the  umbilical  opening,  which 
then  closes  over  it :  but  in  Mammalia  it 
always  remains  on  the  outside ;  and  as 
it  is  emptied  it  contracts  (Fig.  220), 
shrivels  up,  and  together  with  the  part 

of  its  duct  external  to  the  abdomen,  is 

detached  and  disappears  either  before,       Human  embryo  with  um_ 
or  at  the  termination  of  intra-uterine     biiicai  vesicle;  about  the 
life,  the  period  of  its  disappearance  vary-     fifth  week  (after  Daiton  . 
ing  in  different  orders  of  Mammalia. 

When  bloodvessels  begin  to  be  developed,  they  ramify 
largely  over  the  walls  of  the  umbilical  vesicle,  and  are  actively 
concerned  in  absorbing  its  contents,  and  conveying  them  away 
for  the  nutrition  of  the  embryo. 

The  Amnion  and  Allantois. 

At  an  early  stage  of  development  of  the  foetus,  and  some 
time  before  the  completion  of  the  changes  which  have  been 
just  described,  two  important  structureSj  called  respectively 
the  amnion  and  the  allantois,  begin  to  be  formed — the  amnion 
being  developed  by  the  external,  and  the  allantois  by  the  in- 
ternal layer  of  the  blastodermic  membrane. 

The  amnion  is  produced  in  the  following  manner:  The  ex- 
ternal layer  of  the  blastodermic  membrane  is  raised  up  in  the 
form  of  a  fold  around  the  body  of  the  embryo,  so  that  the 


586 


GENERATION  AND  DEVELOPMENT. 


latter  appears  as  if  sunk  in  a  kind  of  depression,  with  the 
outer  layer  of  the  membrane  raised  up  wall-like  around  it. 
On  section,  the  appearance  is  that  represented  in  Fig.  221. 

Soon  the  edges  of  the  fold,  rising  higher  and  higher  above 
and  around  the  embryo,  coalesce  over  it ;  and  the  double  layer 
of  membrane  at  their  place  of  junction  being  absorbed,  the 

Fm.  221. 


FIG.  221.— Diagram  of  fecundated  egg  (after  Dalton).  a,  umbilical  vesicle  ;  b,  am- 
niotic  cavity  ;  c,  allantois. 

FIG.  222.— Fecundated  egg  with  allantois  nearly  complete,  a,  inner  layer  of  am- 
niotic  fold;  b,  outer  layer  of  ditto;  c,  point  where  the  amniotic  folds  come  in  con- 
tact. The  allautois  is  seen  penetrating  between  the  outer  and  inner  layers  of  the 
amniotic  folds.  This  figure,  which  represents  only  the  amniotic  folds  and  the  parts 
within  them,  should  be  compared  with  Figs.  223,  224,  in  which  will  be  found  the 
structures  external  to  these  folds. 

two  layers  of  which  the  fold  was  originally  made  up  are  sep- 
arated from  each  other  (Figs.  223,  224).  The  inner  of  the  two 
forms  the  amnion,  and  remains  continuous  with  the  integu- 
ment of  the  foetus  at  the  umbilicus;  while  the  outer  layer, 
receding  farther  and  farther,  is  fused,  and  forms  one  with  the 
inner  surface  of  the  original  vitelline  membrane,  which  in  the 
meantime  has  undergone  various  alterations,  to  be  immediately 
described  (p.  588). 

As  the  term  of  pregnancy  advances,  the  amnion  becomes 
more  and  more  separated  from  the  body  of  the  foetus  by  a  con- 
siderable quantity  of  fluid,  the  so-called  liquor  amnii. 

During  the  process  of  development  of  the  amnion,  the  allan- 
tois (c,  Fig.  222)  begins  to  be  formed.  Growing  out  from,  or 
near  the  hinder  portion  of  the  intestinal  canal,  with  which  it 
communicates,  it  is  at  first  a  pear-shaped  mass  of  cells ;  but 
becoming  vesicular,  and  very  soon  simply  membranous  and 
vascular,  it  insinuates  itself  between  the  araniotic  folds,  just 
described,  and  comes  into  close  contact  and  union  with  the 
outer  of  the  two  folds,  which  has  itself,  as  before  said,  become 
one  with  the  external  investing  membrane  of  the  egg.  As  it 
grows,  the  allantois  becomes  exceedingly  vascular,  and  in  birds 


THE    URACHUS. 


587 


(Fig.  222s)  envelops  the  whole  embryo — taking  up  vessels, 
so  to  speak,  to  the  outer  investing  membrane  of  the  egg,  and 
lining  the  inner  surface  of  the  shell  with  a  vascular  membrane  ; 
by  these  means  affording  an  extensive  surface  in  which  the 
blood  may  be  aerated.  In  the  human  subject,  and  in  other 
mammalia,  the  vessels  carried  out  by  the  allantois  are  distrib- 
uted only  to  a  special  part  of  the  outer  membrane,  at  which  a 
structure  called  the  placenta  is  developed. 

In  Mammalia,  as  the  visceral  laminae  close  in  the  abdominal 
cavity,  the  allantois  is  thereby  divided  at  the  umbilicus  into 
two  portions ;  the  outer  part,  extending  from  the  umbilicus  to 
the  chorion  (p.  588),  soon  shrivelling ;  while  the  inner  part, 
remaining  in  the  abdomen,  is  in  part  converted  into  the  urin- 


FlG.  223. 


FIG.  224. 


a,  chorion  with  villi.  The  villi  are  shown-  to  be  best  developed  in  the  part  of  the 
chorion  to  which  the  allantois  is  extending;  this  portion  ultimately  becomes  the 
placenta,  b,  space  between  the  two  layers  of  the  amnion.  c,  amniotic  cavity,  d, 
situation  of  the  intestine,  showing  its  connection  with  the  umbilical  vesicle,  e,  um- 
bilical vesicle.  /,  situation  of  heart  and  vessels,  g,  allantois  (after  Todd  and  Bowman). 

ary  bladder;  the  portion  of  the  inner  part,  not  so  converted, 
extending  from  the  bladder  to  the  umbilicus,  under  the  name 
of  the  urachus.  After  birth,  the  umbilical  cord,  and  with  it 
the  external  and  shrivelled  portion  of  the  allantois,  are  cast 
off  at  the  umbilicus,  while  the  urachus  remains  as  an  imper- 
vious cord  stretched  from  the  top  of  the  urinary  bladder  to  the 
umbilicus,  in  the  middle  line  of  the  body,  immediately  be- 
neath the  parietal  layer  of  the  peritoneum.  It  is  sometimes 
enumerated  among  the  ligaments  of  the  bladder. 

It  must  not  be  supposed  that  the  phenomena  which  have 
been  successively  described,  occur  in  any  regular  order  one 
after  another.  On  the  contrary,  the  development  of  one  part 
is  going  on  side  by  side  with  that  of  another. 


588          GENERATION    AND    DEVELOPMENT. 


Development  of  Bloodvessels. 

At  an  early  period  of  development,  and  during  the  changes 
just  described,  an  accumulation  of  cells  ensues  between  the 
mucous  and  serous  laminae  at  a  part  of  the  germinal  mem- 
brane named  the  area  vasculosa  (b,  Fig.  218).  Within  this 
mass,  which  constitutes  a  third  or  middle  layer  of  the  blasto- 
dermic  membrane,  is  laid  the  foundation  for  the  development 
of  the  vascular  system.  At  the  circumference  of  the  vascular 
area,  insulated  red  spots  and  lines  make  their  appearance,  and 
these  soon  unite,  so  as  to  form  a  network  of  vessels  filled  with 
blood.  The  margin  of  the  vascular  layer  is  at  first  limited  and 
quite  circular,  being  bounded  by  vessels  united  in  a  cireulus 
venosus,  or  sinus  terminalis,  but  it  soon  extends  over  the  whole 
surface  of  the  germinal  membrane. 

At  about  the  same  time,  the  rudimentary  heart  is  formed  in 
the  same  layer  of  the  germinal  membrane.  As  shown  by 
Schwann,  the  bloodvessels  are  developed  originally  from  nu- 
cleated cells.  These  cells  sent  out  processes  ;  the  processes 
from  different  cells  unite ;  and  in  this  way  ramifications  and  a 
network  are  produced — vessels  extending  from  this  network 
in  the  area  vasculosa  into  the  area  pellucida,  and  joining  the 
rudimentary  heart  (see  p.  599). 

The  Chorion. 

It  has  been  already  remarked  that  the  allantois  is  a  structure 
which  extends  from  the  body  of  the  foetus  to  the  outer  in- 
vesting membrane  of  the  ovum,  that  it  insinuates  itself  be- 
tween the  two  layers  of  the  amniotic  fold,  and  becomes  fused 
with  the  outer  layer,  which  has  itself  become  previously 

fused  with  the  vitelline  membrane. 
FIG.  225.  By  these  means   the   external  in- 

vesting membrane  of  the  ovum,  or 
the  chorion,  as  it  is  now  called, 
represents  three  layers,  namely,  the 
original  vitelline  membrane,  the 
outer  layer  of  the  amniotic  fold, 
and  the  allantois. 

Very  soon  after  the  entrance  of 
the  ovum  into  the  uterus,  in  the 
human  subject,  the  outer  surface 
of  the  chorion  is  found  beset  with 
fine  processes,  the  so-called  villi  of 
the  chorion  (a,  Figs.  223,  224),  which 
give  it  a  rough  and  shaggy  ap- 
pearance. At  first  only  cellular  in 


THE  GLANDS  OF  THE  UTERUS.       589 

structure,  these  little  outgrowths  subsequently  become  vascular 
by  the  development  in  them  of  loops  of  capillaries  (Fig.  225)  ; 
and  the  latter  at  length  form  the  minute  extremities  of  the 
bloodvessels  which  are,  so  to  speak,  conducted  from  the  foetus 
to  the  chorion  by  the  allantois.  The  function  of  the  villi  of 
the  chorion  is  evidently  the  absorption  of  nutrient  matter  for 
the  fcetus ;  and  this  is  probably  supplied  to  them  at  first  from 
the  fluid  matter  secreted  by  the  follicular  glands  of  the  uterus, 
in  which  they  are  soaked.  Soon,  however,  the  foetal  vessels 
of  the  villi  come  into  more  intimate  relation  with  the  vessels 
of  the  uterus.  The  part  at  which  this  relation  between  the 
vessels  of  the  foetus  and  those  of  the  parent  ensues,  is  not,  how- 
ever, over  the  whole  surface  of  the  chorion :  for,  although  all 
the  villi  become  vascular,  yet  they  become  indistinct  or  dis- 
appear except  at  one  part  where  they  are  greatly  developed, 
and  by  their  branching  give  rise,  with  the  vessels  of  the  uterus, 
to  the  formation  of  the  placenta. 

To  understand  the  manner  in  which  the/te&z/  and  maternal 
bloodvessels  come  into  relation  with  each  other  in  the  pla- 
centa, it  is  necessary  briefly  to  notice  the  changes  which  the 
uterus  undergoes  after  impregnation.  These  changes  consist 
especially  of  alterations  in  structure  of  the  superficial  part  of 
the  mucous  membrane  which  lines  the  interior  of  the  uterus, 
and  which  forms,  after  a  kind  of  development  to  be  immedi- 
ately described,  the  membrana  deddua,  so  called  on  account 
of  its  being  discharged  from  the  uterus  at  the  period  of  partu- 
rition. 

Changes  of  the  Mucous  Membrane  of  the  Uterus,  and  Formation 
of  the  Placenta. 

The  mucous  membrane  of  the  human  uterus  is  abundantly 
beset  with  tubular  follicles,  arranged  perpendicularly  to  the 
surface.  These  follicles  are  very  small  in  the  unimpregnated 
uterus  ;  but  when  examined  shortly  after  impregnation,  they 
are  found  elongated,  enlarged,  and  much  waved  and  contorted 
towards  their  deep  and  closed  extremity,  which  is  implanted 
at  some  depth  in  the  tissue  of  the  uterus,  and  commonly  dilates 
into  two  or  three  closed  sacculi  (Fig.  226). 

According  to  Dr.  Sharpey,  the  glands  of  the  mucous  mem- 
brane of  the  bitch's  uterus  (and  according  to  H.  Miiller,  that 
of  the  human  female  also)  are  of  two  kinds,  simple  and  com- 
pound. The  former,  which  are  the  more  numerous,  are  merely 
very  short  unbranched  tubes  closed  atone  end  (Fig.  227, 1, 1,), 
the  latter  (2,  2)  have  a  long  duct  dividing  into  convoluted 
branches ;  both  open  on  the  inner  surface  of  the  membrane  by 

50 


590 


GENERATION  AND  DEVELOPMENT. 


small  round  orifices,  lined  with  epithelium  and  set  closely  to- 
gether. 

On  the  internal  surface  of  the  mucous  membrane  may  be 
seen  the  circular  orifices  of  the  glands,  many  of  which  are,  in 


FIG.  226. 


Section  of  the  lining  membrane  of  a  human  uterus  at  the  period  of  commencing 
pregnancy,  showing  the  arrangement  and  other  peculiarities  of  the  glands,  d,  d,  d, 
with  their  orifices,  a,  a,  a,  on  the  internal  surface  of  the  organ.  Twice  the  natural 
size. 

the  early  period  of  pregnancy,  surrounded  by  a  whitish  ring, 
formed  of  the  epithelium  which  lines  the  follicles  (Fig.  228). 


FIG.  227. 


FIG.  228. 


FIG.  227.— A  vertical  section  of  the  mucous  membrane,  showing  uterine  glands  of 
the  bitch,  magnified  twelve  diameters;  1,  1,  simple  glands;  2,  2,  compound  ditto 
(from  Sharpey). 

FIG.  228. — Two  thin  segments  of  human  decidua  after  recent  impregnation,  viewed 
on  a  dark  ground  :  they  show  the  openings  on  the  surface  of  the  membrane.  A  is 
magnified  six  diameters,  and  B  twelve  diameters.  At  1,  the  lining  of  epithelium  is 
seen  within  the  orifices,  at  2  it  has  escaped  (from  Sharpey). 

Coincidently  with  the  increasing  size  of  the  follicles,  the 
quantity  of  their  secretion  is  augmented,  the  vessels  of  the 
mucous  membrane  become  larger  and  more  numerous,  while  a 
substance  composed  chiefly  of  nucleated  cells  fills  up  the  inter- 


THE    PLACENTA.  591 

foil icular  spaces  in  which  the  bloodvessels  are  contained.  The 
effect  of  these  changes  is  an  increased  thickness,  softness,  and 
vascularity  of  the  mucous  membrane,  the  superficial  part  of 
which  itself  forms  the  membrana  decidua. 

The  object  of  this  increased  development  seems  to  be  the 
production  of  nutritive  materials  for  the  ovum  ;  for  the  cavity 
of  the  uterus  shortly  becomes  filled  with  secreted  fluid,  consist- 
ing almost  entirely  of  nucleated  cells,  in  which  the  villi  of  the 
chorion  are  imbedded. 

When  the  ovum  first  enters  the  uterus  it  becomes  imbedded 
in  the  structure  of  the  decidua,  which  is  yet  quite  soft,  and  in 
which  soon  afterwards  three  portions  are  distinguishable.  These 
have  been  named  the  decidua  vera,  the  decidua  reflexa,  and 
the  decidua  serotina.  The  first  of  these,  the  decidua  vera, 
lines  the  cavity  of  the  uterus;  the  second,  or  decidua  reflexa, 
is  a  part  of  the  decidua  vera,  which  grows  up  around  the  ovum, 
and,  wrapping  it  closely,  forms  its  immediate  investment.  The 
third,  or  decidua  serotina,  is  the  part  of  the  decidua  vera  which 
becomes  especially  developed  in  connection  with  those  villi  of 
the  choriori  which,  instead  of  disappearing,  remain  to  form  the 
foetal  part  of  the  placenta. 

As  the  ovum  increases  in  size,  the  decidua  vera  and  the 
decidua  reflexa  gradually  come  into  contact,  and  in  the  third 
month  of  pregnancy  the  cavity  between  them  has  quite  disap- 
peared. Henceforth  it  is  very  difficult,  or  even  impossible,  to 
distinguish  the  two  layers. 

During  these  changes  the  deeper  part  of  the  mucous  mem- 
brane of  the  uterus,  at  and  near  the  region  where  the  placenta 
is  placed,  becomes  hollowed  out  by  sinuses,  or  cavernous  spaces, 
which  communicate  on  the  one  hand  with  arteries  and  on  the 
other  with  veins  of  the  uterus.  Into  these  sinuses  the  villi  of 
the  chorion  protrude,  pushing  the  thin  wall  of  the  sinus  before 
them,  and  so  come  into  intimate  relation  with  the  blood  con- 
tained in  them.  There  is  no  direct  communication  between 
the  bloodvessels  of  the  mother  and  those  of  the  foetus  ;  but  the 
layer  or  layers  of  membrane  intervening  between  the  blood  of 
the  one  and  of  the  other  offer  no  obstacle  to  a  free  interchange 
of  matters  between  them.  Thus  the  villi  of  the  chorion,  con- 
taining foetal  blood,  are  bathed  or  soaked  in  maternal  blood 
contained  in  the  uterine  sinuses.  The  arrangement  may  be 
roughly  compared  to  filling  a  glove  with  foetal  blood,  and 
dipping  its  fingers  into  a  vessel  containing  maternal  blood. 
But  in  the  foetal  villi  there  is  a  constant  stream  of  blood 
into  and  out  of  the  loop  of  capillary  bloodvessel  contained  in 
it,  as  there  is  also  into  and  out  of  the  maternal  sinuses. 

It  would  seem  from  the  observations  of  Professor  Goodsir, 


592         GENERATION    AND    DEVELOPMENT. 

that,  at  the  villi  of  the  placental  tufts,  where  the  foetal  and 
maternal  portions  of  the  placenta  are  brought  into  close  rela- 
tion with  each  other,  the  blood  in  the  vessels  of  the  mother  is 
separated  from  that  in  the  vessels  of  the  fetus  by  the  inter- 
vention of  two  distinct  sets  of  nucleated  cells  (Fig.  229).  One 
of  these  (6)  belongs  to  the  maternal  portion  of  the  placenta,  is 
placed  between  the  membrane  of  the  villus  and  that  of  the 
vascular  system  of  the  mother,  and  is  probably  designed  to 
separate  from  the  blood  of  the  parent  the  materials  destined 
for  the  blood  of  the  foetus ;  the  other  (/)  belongs  to  the  foetal 
portion  of  the  placenta,  is  situated  between  the  membrane  of 
the  villus  and  the  loop  of  vessels  contained  within,  and  prob- 
ably serves  for  the  absorption  of  the  material  secreted  by  the 
other  sets  of  cells,  and  for  its  conveyance  into  the  bloodvessels 
of  the  foetus.  Between  the  two  sets  of  cells  with  their  invest- 
ing membrane  there  exists  a  space  (cT),  into  which  it  is  proba- 
ble that  the  materials  secreted  by 
FIG.  229.  -the  one  set  of  cells  of  the  villus 

are  poured  in  order  that  they  may 
be  absorbed  by  the  other  set,  and 
thus  conveyed  into  the  foetal  ves- 
sels. 

Not  only,  however,  is  there  a 
passage  of  materials  from  the 
blood  of  the  mother  into  that  of 
the  foetus,  but  there  can  be  no 

Extremity  of  a  placental  villus.  a,    doubt  of    the    existence   of    a    mu- 

lining  membrane  of  the  vascular  tual  interchange  of  materials  be- 

system  of  the  mother;  ft,  cells  im-    ,  ji       r  i       j  r     .1       .<?  j?    j.  j 

mediately  lininga;  d,  space  between    tween  the  Wood  both  of  fotUS  and 

the  maternal  and  fetal  portions  of  of  parent,  the  latter  supplying  the 
the  villus ;  e,  internal  membrane  of  former  with  nutriment,  and  in  turn 
the  villus,  or  external  membrane  of  abstracting  from  it  materials  which 

the  chorion  ;  /,  internal  cells  of  the  require  to  be  removed.  Dr.  Alex- 
villus.  or  cells  of  the  chorion  ;  a,  loop  j  -rr  •> 

of  umbilical  vessel  (after  Goodsir).     andei\  Harvey  s  experiments  were 

very  decisive  on  this  point,  ihe 
view  has  also  received  abundant 

support  of  late  from  Mr.  Hutchinson's  important  observations 
on  the  communication  of  syphilis  from  the  father  to  the  mother, 
through  the  instrumentality  of  the  foetus  ;  and  still  more  from 
Mr.  Savory's  experimental  researches,  which  prove  quite  clearly 
that  the  female  parent  may  be  directly  inoculated  through  the 
foetus.  Having  opened  the  abdomen  and  uterus  of  a  pregnant 
bitch,  Mr.  Savory  injected  a  solution  of  strychnia  into  the 
abdominal  cavity  of  one  foetus,  and  into  the  thoracic  cavity  of 
another,  and  then  replaced  all  the  parts,  every  precaution 
being  taken  to  prevent  escape  of  the  poison.  In  less  than 


THE    PLACENTA.  593 

half  an  hour,  the  bitch  died  from  tetanic  spasms ;  the  foetuses 
operated  on  were  also  found  dead,  while  the  others  were  alive 
and  active.  The  experiments,  repeated  on  other  animals  with 
like  results,  leave  no  doubt  of  the  rapid  and  direct  transmis- 
sion of  matter  from  the  foetus  to  the  mother,  through  the  blood 
of  the  placenta. 

The  placenta,  therefore,  of  the  human  subject  is  composed 
of  a,  fatal  part  and  a  maternal  part, — the  term,  placenta,  prop- 
erly including  all  that  entanglement  of  foetal  villi  and  mater- 
nal sinuses,  by  means  of  which  the  blood  of  the  foetus  is  en- 
riched and  purified  after  the  fashion  necessary  for  the  proper 
growth  and  development  of  those  parts  which  it  is  destined  to 
nourish. 

The  whole  of  this  structure  is  not,  as  might  be  imagined, 
thrown  off  immediately  after  birth.  The  greater  part,  indeed, 
comes  away  at  that  time,  as  the  afterbirth,  and  the  separation 
of  this  portion  takes  place  by  a  rending  or  crushing  through 
of  that  part  at  which  its  cohesion  is  least  strong,  namely,  where 
it  is  most  burrowed  and  undermined  by  the  cavernous  spaces 
before  referred  to.  In  this  way  it  is  cast  off  with  the  foetal 
membranes  and  the  decidua  vera  and  reflexa,  together  with  a 
part  of  the  decidua  serotina.  The  remaining  portion  withers, 
and  disappears  by  being  gradually  either  absorbed,  or  thrown 
off  in  the  uterine  discharges  or  the  lochia,  which  occur  at  this 
period. 

A  new  mucous  membrane  is  of  course  gradually  developed, 
as  the  old  one,  by  its  peculiar  transformation  into  what  is 
called  the  decidua,  ceases  to  perform  its  original  functions. 

The  umbilical  cord,  which  in  the  latter  part  of  foetal  life  is 
almost  solely  composed  of  the  two  arteries  and  the  single  vein 
which  respectively  convey  foetal  blood  to  and  from  the  pla- 
centa, contains  the  remnants  of  other  structures  which  in  the 
early  stages  of  the  development  of  the  embryo  were,  as  already 
related,  of  great  comparative  importance.  Thus,  in  early 
foetal  life,  it  is  composed  of  the  following  parts :  (1.)  Exter- 
nally, a  layer  of  the  amnion,  reflected  over  it  from  the  um- 
bilicus. (2.)  The  umbilical  vesicle  with  its  duct  and  apper- 
taining omphalo-mesenteric  bloodvessels.  (3.)  The  remains 
of  the  allantois,  and  continuous  with  it  the  urachus.  (4.) 
The  umbilical  vessels,  which  as  just  remarked,  ultimately  form 
the  greater  part  of  the  cord. 

DEVELOPMENT    OF    ORGANS. 

It  remains  now  to  consider  in  succession  the  development 
of  the  several  organs  and  systems  of  organs  in  the  further  prog- 
ress of  the  embryo. 


594          GENERATION    AND     DEVELOPMENT. 

Development  of  the  Vertebral  Column  and  Cranium. 

The  primitive  part  of  the  vertebral  column  in  all  the  Ver- 
tebrata  is  the  gelatinous  chorda  dorsalis,  which  consists  entirely 
of  cells.  This  cord  tapers  to  a  point  at  the  cranial  and  caudal 
extremities  of  the  animal.  In  the  progress  of  its  development, 
it  is  found  to  become  inclosed  in  a  membranous  sheath,  which 
at  length  acquires  a  fibrous  structure,  composed  of  transverse 
annular  fibres.  The  chorda  dorsalis  is  to  be  regarded  as  the 
azygos  axis  of  the  spinal  column,  and,  in  particular,  of  the 
future  bodies  of  the  vertebrae,  although  it  never  itself  passes 
into  the  cartilaginous  or  osseous  state,  but  remains  inclosed  as 
in  a  case  within  the  persistent  parts  of  the  vertebral  column 
which  are  developed  around  it.  It  is  permanent,  however, 
only  in  a  few  animals:  in  the  majority  it  disappears  at  an 
early  period. 

The  cartilaginous  or  osseous  vertebrae  are  always  first  de- 
veloped in  pairs  of  lateral  elements  at  the  sides  of  the  chorda 
dorsalis.  From  these  lateral  elements  are  formed  the  bodies 
and  the  arches  of  the  vertebrae.  In  some  animals,  as  the  stur- 
geon, however,  the  lateral  elements  of  the  vertebrae  undergo 
no  further  development,  and  it  is  here  that  the  chorda  dorsalis 
is  persistent  through  life.  In  the  myxinoid  fishes  the  spinal 
column  presents  no  vertebral  segments,  and  there  exists  merely 
the  chorda  dorsalis  with  the  fibrous  layer  surrounding  its 
sheath,  which  is  the  layer  in  which  the  skeleton  originates. 
This  fibrous  layer  also  forms  superiorly  the  membranous  cover- 
ing of  the  vertebral  canal. 

In  reptiles,  birds,  and  mammals,  the  mode  in  which  the 
vertebrae  are  formed  around  the  chorda  dorsalis  seems  to  be 
different.  When  the  formation  of  these  parts  from  the  blastema 
commences,  there  appears  at  each  side  of  the  chorda  dorsalis 
a  series  of  quadrangular  figures,  the  rudiments  of  the  future 
vertebrae.  These  gradually  increase  in  number  and  size,  so 
as  to  surround  the  chorda  both  above  and  below,  sending  out, 
at  the  same  time,  superiorly,  processes  to  form  the  arches  des- 
tined to  inclose  the  spinal  cord.  In  this  primitive  condition 
the  body  and  arches  of  each  vertebra  are  formed  by  one  piece 
on  each  side.  At  a  certain  period  these  two  primary  elements, 
which  have  become  cartilaginous,  unite  iuferiorly  by  a  suture. 
The  chorda  is  now  inclosed  in  a  case,  formed  by  the  bodies  of 
the  vertebrae,  but  it  gradually  wastes  and  disappears.  Before 
the  disappearance  of  the  chorda,  the  ossification  of  the  bodies 
and  arches  of  the  vertebrae  begins  at  distinct  points. 

The  ossification  of  the  body  of  a  vertebra  is  first  observed 
at  the  point  where  the  two  primitive  elements  of  the  vertebrae 


FACE     AND    VISCERAL     ARCHES.  595 

have  united  inferiorly.  Those  vertebrae  which  do  not  bear 
ribs,  such  as  the  cervical  vertebrae,  have  generally  an  additional 
centre  of  ossification  in  the  transverse  process,  which  is  to  be 
regarded  as  an  abortive  rudiment  of  a  rib.  In  the  foetal  bird, 
these  additional  ossified  portions  exist  in  all  the  cervical  ver- 
tebrae, and  gradually  become  so  much  developed  in  the  lower 
part  of  the  cervical  region  as  to  form  the  upper  false  ribs  of 
this  class  of  animals.  The  same  parts  exist  in  mammalia  and 
man ;  those  of  the  last  cervical  vertebrae  are  the  most  developed, 
and  in  children  may,  for  a  considerable  period,  be  distinguished 
as  a  separate  part  on  each  side,  like  the  root  or  head  of  a  rib. 
The  true  cranium  is  a  prolongation  of  the  vertebral  column, 
and  is  developed  at  a  much  earlier  period  than  the  facial  bones. 
Originally,  it  is  formed  of  but  one  mass,  a  cerebral  capsule, 
the  chorda  dorsalis  being  continued  into  its  base,  and  ending 
there  with  a  tapering  point.  This  relation  of  the  chorda  dor- 
salis to  the  basis  of  the  cranium  is  persistent  through  life  in 
some  fish,  e.  g.,  the  sturgeon.  The  first  appearance  of  a  solid 
support  at  the  base  of  the  cranium  observed  by  Miiller  in  fish, 
consists  of  two  elongated  bands  of  cartilage,  one  on  the  right 
and  the  other  on  the  left  side,  which  are  connected  with  the 
cartilaginous  capsule  of  the  auditory  apparatus,  and  united 
with  each  other  in  an  arched  manner  anteriorly  beneath  the 
anterior  end  of  the  cerebral  capsule.  Hence,  in  the  cranium, 
as  in  the  spinal  column,  there  are  at  first  developed  at  the 
sides  of  the  chorda  dorsalis  two  symmetrical  elements,  which 
subsequently  coalesce,  and  may  wholly  inclose  the  chorda.1 

Development  of  the  Face  and  Visceral  Arches. 

It  has  been  said  before  that  at  an  early  period  of  develop- 
ment of  the  embryo,  there  grow  up  on  the  sides  of  the  primi- 
tive groove  the  so-called  dorsal  lamince,  which  at  length 
coalesce,  and  complete  by  their  union  the  spinal  canal.  The 
same  process  essentially  takes  place  in  the  head,  so  as  to  in- 
close the  cranial  cavity. 

The  so-called  visceral  lamince  have  been  also  described  as 
passing  forwards,  and  gradually  coalescing  in  front,  as  the 
dorsal  laminae  do  behind,  and  thus  inclosing  the  thoracic  and 
abdominal  cavity.  An  analogous  process  occurs  in  the  facial 
and  cervical  regions,  but  the  inclosing  laminae,  instead  of  being 
simple,  as  in  the  former  instances,  are  cleft. 

1  For  much  new  and  original  matter  relating  to  the  development 
of  the  cranium,  the  reader  is  referred  to  the  important  lectures  on 
Comparative  Anatomy,  delivered  at  the  College  of  Surgeons  by  Pro- 
fessor Huxley. 


596          GENERATION    AND     DEVELOPMENT. 

In  this  way  the  so-called  visceral  arches  and  clefts  are  formed, 
four  on  each  side  (Fig.  230,  A),  and  from  or  in  connection  with 
these  arches  the  following  parts  are  developed : 

From  the  first  arch,  and  its  maxillary  process,  the  superior 
maxillary,  the  palate  bone,  and  the  internal  pteryyoid  plate  of 
the  sphenoid  bone,  the  incus  and  malleus  and  the  lower  jaw. 

FlG.  230. 


A,  magnified  view  from  before  of  the  head  and  neck  of  a  human  embryo  of  about 
three  weeks  (from  Ecker) — 1,  anterior  cerebral  vesicle  or  cerebrum ;  2,  middle  ditto ; 
3,  middle  or  fronto-nasal  process ;  4,  superior  maxillary  process ;  5,  eye ;  6,  inferior 
maxillary  process,  or  first  visceral  arch,  and  below  it  the  first  cleft;  7,  8,  9,  second, 
third,  and  fourth  arches  and  clefts.  B,  anterior  view  of  the  head  of  a  human  foatus  of 
about  the  fifth  week  (from  Ecker,  as  before,  Fig.  IV).  1,  2,  3,  5,  the  same  parts  as 
in  A;  4,  the  external  nasal  or  lateral  frontal  process;  6,  the  superior  maxillary  pro- 
cess ;  7,  the  lower  jaw ;  X ,  the  tongue ;  8,  first  branchial  cleft  becoming  the  meatus 
auditorius  externus. 

The  upper  part  of  the  face  in  the  middle  line  is  developed 
from  the  so-called  fronto-nasal  process  (A,  3,  Fig.  230).  From 
the  second  arch  are  developed  the  stapes,  the  stapedius  muscle, 
the  styloid  process  of  the  temporal  bone,  the  stylo-hyoid  liga- 
ment, and  the  smaller  cornu  of  the  hyoid  bone.  From  the  third 
visceral  arch,  the  greater  cornu  and  body  of  the  hyoid  bone. 
In  man  and  other  mammalia  the  fourth  visceral  arch  is  indis- 
tinct. 

Development  of  the  Extremities. 

The  extremities  are  developed  in  a  uniform  manner  in  all 
vertebrate  animals.  They  appear  in  the  form  of  leaflike  ele- 
vations from  the  parietes  of  the  trunk  (see  Fig.  231),  at  points 
where  more  or  less  of  an  arch  will  be  produced  for  them  within. 
The  primitive  form  of  the  extremity  is  nearly  the  same  in  all 
Vertebrata,  whether  it  be  destined  for  swimming,  crawling, 
walking,  or  flying.  In  the  human  foetus  the  fingers  are  at  first 


DEVELOPMENT  OF  VASCULAR  SYSTEM.   597 

united,  as  if  webbed  for  swimming ;  but  this  is  to  be  regarded 
not  so  much  as  an  approximation  to  the  form  of  aquatic  ani- 


FlG.  231. 


'•if 


A  human  embryo  of  the  fourth  week,  3^  lines  in  length.  1,  the  chorion ;  3,  part 
of  the  amnion  ;  4,  umbilical  vesicle  with  its  long  pedicle  passing  into  the  abdomen ; 
7,  the  heart ;  8,  the  liver ;  9,  the  visceral  arch  destined  to  form  the  lower  jaw,  be- 
neath which  are  two  other  visceral  arches  separated  by  the  branchial  clefts ;  10,  ru- 
diment of  the  upper  extremity;  11,  that  of  the  lower  extremity;  12,  the  umbilical 
cord  ;  15,  the  eye ;  16,  the  ear  ;  17,  the  cerebral  hemispheres ;  18,  the  optic  lobes  or 
corpora  quadrigemina. 

mals,  as  the  primitive  form  of  the  hand,  the  individual  parts 
of  which  subsequently  become  more  completely  isolated. 

Development  of  the   Vascular  System. 

The  first  development  of  the  vascular  system  and  heart  in 
the  germinal  membrane  has  been  already  alluded  to  (p.  588). 
The  earliest  form  of  the  heart  presents  itself  as  a  solid  com- 
pact mass  of  embryonic  cells,  similar  to  those  of  which  the 
other  organs  of  the  body  are  constituted.  It  is  at  first  un- 
provided with  a  cavity ;  but  this  shortly  makes  its  appearance, 
resulting  apparently  from  the  separation  from  each  other  of 
the  cells  of  the  central  portion.  A  liquid  is  now  formed  in 
the  still  closed  cavity,  and  the  central  cells  may  be  seen  float- 
ing within  it.  These  contents  of  the  cavity  are  soon  observed  to 
be  propelled  to  and  fro  with  a  tolerable  degree  of  regularity, 
owing  to  the  commencing  pulsations  of  the  heart.  These  pul- 
sations take  place  even  before  the  appearance  of  a  cavity,  and 
immediately  after  the  first  "  laying  down"  of  the  cells  from 
which  the  heart  is  formed.  At  first  they  seldom  exceed  from 
fifteen  to  eighteen  in  the  minute.  The  fluid  within  the  cavity 


598 


GENERATION  AND  DEVELOPMENT. 


of  the  heart  shortly  assumes  the  characters  of  blood.  At  the 
same  time  the  cavity  itself  forms  a  communication  with  the 
great  vessels  in  contact  with  it,  and  the  cells  of  which  its  wall 


FIG.  232. 


Capillary  bloodvessels  of  the  tail  of  a  young  larval  frog.  Magnified  350  times 
(after  Kolliker). — a,  capillaries  permeable  to  blood  ;  b,  fat-granules  attached  to  the 
walls  of  the  vessels,  and  concealing  the  nuclei ;  c,  hollow  prolongation  of  a  capillary 
ending  in  a  point ;  d,  a  branching  cell  with  nucleus  and  fat-granules ;  it  communi- 
cates by  three  branches  with  prolongation  of  capillaries  already  formed  ;  e,  e,  blood- 
corpuscles  still  containing  granules  of  fat. 


are  composed  are  transformed  into  fibrous  and  muscular  tis- 
sues, and  into  epithelium. 

Bloodvessels  appear  to  be  developed  in  two  ways,  according 
to  the  size  of  the  vessels.     In  the  formation  of  large  bloodves- 


DEVELOPMENT    OF    VASCULAR    SYSTEM.       599 

sels,  masses  of  embryonic  cells  similar  to  those  from  which  the 
heart  and  other  structures  of  the  embryo  are  developed,  ar- 
range themselves  in  the  position,  form,  and  thickness  of  the 
developing  vessel.  Shortly  afterwards  the  cells  in  the  interior 
of  a  column  of  this  kind  seem  to  be  developed  into  blood-cor- 
puscles, while  the  external  layer  of  cells  is  converted  into  the 
walls  of  the  vessel. 

In  the  development  of  capillaries  another  plan  is  pursued. 
This  has  been  well  illustrated  by  Kolliker,  as  observed  in 
the  tails  of  tadpoles.  The  first  lateral  vessels  of  the  tail  have 
the  form  of  simple  arches,  passing  between  the  main  artery 
and  vein,  and  are  produced  by  the  junction  of  prolongations, 
sent  from  both  the  artery  and  vein,  with  certain  elongated  or 
star-shaped  cells,  in  the  substance  of  the  tail.  When  these 
arches  are  formed  and  are  permeable  to  blood,  new  prolonga- 
tions pass  from  them,  join  other  radiated  cells,  and  thus  form 
secondary  arches.  In  this  manner,  the  capillary  network  ex- 
tends in  proportion  as  the  tail  increases  in  length  and  breadth, 
and  it,  at  the  same  time,  becomes  more  dense  by  the  formation, 
according  to  the  same  plan,  of  fresh  vessels  within  its  meshes. 
The  prolongations  by  which  the  vessels  communicate  with  the 
star-shaped  cells,  consist  at  first  of  narrow-pointed  projections 
from  the  side  of  the  vessels,  which  gradually  elongate  until 
they  come  in  contact  with  the  radiated  processes  of  the  cells. 
The  thickness  of  such  a  prolongation  often  does  not  exceed 
that  of  a  fibril  of  fibrous  tissue,  and  at  first  it  is  perfectly 
solid ;  but,  by  degrees,  especially  after  its  junction  with  a  cell, 
or  with  another  prolongation,  or  with  a  vessel  already  per- 
meable to  blood,  it  enlarges,  and  a  cavity  then  forms  in  its  in- 
terior (see  Fig.  232).  With  Kolliker's  account,  our  own  ob- 
servations, made  on  the  fine  gelatinous  tissue  conveying  the 
umbilical  vessels  of  a  sheep's  embryo  to  the  uterine  cotyledons, 
completely  accord.  This  tissue  is  well  calculated  to  illustrate 
the  various  steps  in  the  development  of  bloodvessels  from 
elongating  and  branching  cells. 

About  the  time  that  the  heart  at  its  lowest  extremity  re- 
ceives the  venous  trunks,  and  at  its  upper  extremity  gives  off 
the  large  arterial  trunk,  it  becomes  curved  from  a  straight  into 
a  horseshoe  form,  and  shortly  divides  into  three  cavities  (Fig. 
233).  Of  these  three  cavities,  which  are  developed  in  all 
Vertebrata,  the  most  posterior  is  the  simple  auricle;  themidde 
one  the  simple  ventricle ;  and  the  most  anterior  the  bulbus 
arteriosus.  These  three  parts  of  the  heart  contract  in  succes- 
sion. The  auricle  and  the  bulbus  arteriosus  at  this  period  lie 
at  the  extremities  of  the  horseshoe.  The  bulging  out  of  the 
middle  portion  inferiorly  gives  the  first  indication  of  the  future 


600         GENERATION    AND     DEVELOPMENT. 

form  of  the  ventricle  (see  Fig.  233).  The  great  curvature  of  the 
horseshoe  by  the  same  means  becomes  much  more  developed 
than  the  smaller  curvature  between  the  auricle  and  bulbus; 

FIG.  233. 


Heart  of  the  chick  at  the  45th,  65th,  and  85th  hours,  of  incubation.  1,  the  venous 
trunks;  2,  the  auricle;  3,  the  ventricle;  4,  the  bulbus  arteriosus  (after  Dr.  Allen 
Thomson). 

and  the  two  extremities,  the  auricle  and  bulb,  approach  each 
other  superiorly,  so  as  to  produce  a  greater  resemblance  to  the 
latter  form  of  the  heart,  whilst  the  ventricle  becomes  more 
and  more  developed  inferiorly.  The  heart  of  fishes  retains 
these  three  cavities,  no  further  division  by  internal  septa 
into  right  and  left  chambers  taking  place.  In  Amphibia,  also, 
the  heart  throughout  life  consists  of  the  three  muscular  divi- 
sions which  are  so  early  formed  in  the  embryo ;  but  the  auricle 
is  divided  internally  by  a  septum  into  a  pulmonary  and  sys- 
temic auricle.  In  reptiles,  not  merely  the  auricle  is  thus 
divided  into  two  cavities,  but  a  similar  septum  is  more  or  less 
developed  in  the  ventricle.  In  birds,  mammals,  and  the  human 
subject,  both  auricle  and  ventricle  undergo  complete  division 
by  septa ;  whilst  in  these  animals  as  well  as  in  reptiles,  the 
bulbus  aortse  is  not  permanent,  but  becomes  lost  in  the  ven- 
tricles. The  septum  dividing  the  ventricle  commences  at  the 
apex  and  extends  upwards.  When  it  is  complete,  a  septum 
is  developed  in  the  bulbus  aortse,  separating  the  roots  of  the 
proper  aorta  and  the  pulmonary  artery.  The  septum  of  the 
auricles  is  developed  from  a  semilunar  fold,  which  extends 
from  above  downwards.  In  man,  the  septum  between  the 
ventricles,  according  to  Meckel,  begins  to  be  formed  about  the 
fourth  week,  and  at  the  end  of  eight  weeks  is  complete.  The 
septum  of  the  auricles,  in  man  and  all  animals  which  possess 
it,  remains  imperfect  throughout  foetal  life.  When  the  par- 
tition of  the  auricles  is  first  commencing,  the  two  venae  cavse 
have  different  relations  to  the  two  cavities.  The  superior  cava 
enters,  as  in  the  adult,  into  the  right  auricle ;  but  the  inferior 
cava  is  so  placed  that  it  appears  to  enter  the  left  auricle ;  and 
the  posterior  part  of  the  septum  of  the  auricles  is  formed  by 
the  Eustachian  valve,  which  extends  from  the  point  of  en- 


THE     FCETAL    CIRCULATION.  601 

trance  of  the  inferior  cava.  Subsequently,  however,  the  septum, 
growing  from  above  downwards,  becomes  directed  more  and 
more  to  the  left  of  the  vena  cava  inferior.  During  the  entire 
period  of  foetal  life,  there  remains  an  opening  in  the  septum, 
which  the  valve  of  the  foramen  ovale,  developed  in  the  third 
month,  imperfectly  closes. 

Circulation  of  Blood  in  the  Fcetus. 

The  circulation  of  blood  in  the  foetus  is  peculiar,  and  differs 
considerably  from  that  of  the  adult.  It  will  be  well,  perhaps, 
to  begin  its  description  by  tracing  the  course  of  the  blood, 
which,  after  being  carried  out  to  the  placenta  by  the  two  um- 
bilical arteries,  has  returned,  cleansed  and  replenished,  to  the 
foetus  by  the  umbilical  vein. 

It  is  at  first  conveyed  to  the  under  surface  of  the  liver,  and 
there  the  stream  is  divided, — a  part  of  the  blood  passing 
straight  on  to  the  inferior  vena  cava,  through  a  venous  canal 
called  the  ductus  venosus,  while  the  remainder  passes  into  the 
portal  vein,  and  reaches  the  inferior  vena  cava  only  after  cir- 
culating through  the  liver.  Whether,  however,  by  the  direct 
route  through  the  ductus  venosus  or  by  the  roundabout  way 
through  the  liver, — all  the  blood  which  is  returned  from  the 
placenta  by  the  umbilical  vein  reaches  the  inferior  vena  cava 
at  last,  and  is  carried  by  it  to  the  right  auricle  of  the  heart, 
into  which  cavity  is  also  pouring  the  blood  that  has  circulated 
in  the  head  and  neck  and  arms,  and  has  been  brought  to  .the 
auricle  by  the  superior  vena  cava.  It  might  be  naturally  ex- 
pected that  the  two  streams  of  blood  would  be  mingled  in  the 
right  auricle,  but  such  is  not  the  case,  or  only  to  a  slight  ex- 
tent. The  blood  from  the  superior  vena  cava — the  less  pure 
fluid  of  the  two — passes  almost  exclusively  into  the  right  ven- 
tricle, through  the  auriculo-ventricular  opening,  just  as  it  does 
in  the  adult ;  while  the  blood  of  the  inferior  vena  cava  is  di- 
rected by  a  fold  of  the  lining  membrane  of  the  heart,  called 
the  Eustachian  valve,  through  the  foramen  ovale  into  the  left 
auricle,  whence  it  passes  into  the  left  ventricle,  and  out  of  this 
into  the  aorta,  and  thence  to  all  the  body.  The  blood  of  the 
superior  vena  cava,  which,  as  before  said,  passes  into  the  right 
ventricle,  is  sent  out  thence  in  small  amount  through  the  pul- 
monary artery  to  the  lungs,  and  thence  to  the  left  auricle,  as 
in  the  adult.  The  greater  part,  however,  by  far,  does  not  go 
to  the  lungs,  but  instead,  passes  through  a  canal,  the  ductus 
arteriosus,  leading  from  the  pulmonary  artery  into  the  aorta 
just  below  the  origin  of  the  three  great  vessels  which  supply 
the  upper  parts  of  the  body ;  and  there  meeting  that  part  of 


602 


GENERATION  AND  DEVELOPMENT. 


the  blood  of  the  inferior  vena  cava  which  has  not  gone  into 
these  large  vessels,  it  is  distributed  with  it  to  the  trunk  and 
lower  parts, — a  portion  passing  out  by  way  of  the  two  umbili- 


FIG.  234. 


cal  arteries  to  the  placenta.  From  the  placenta  it  is  returned 
by  the  umbilical  vein  to  the  under  surface  of  the  liver,  from 
which  the  description  started. 

After  birth  the  foramen  ovale  closes,  and  so  do  the  ductus 


DEVELOPMENT  OF  ORGANS  OF  SENSE.   603 

arteriosus  and  ductus  venosus,  as  well  as  the  umbilical  vessels ; 
so  that  the  two  streams  of  blood  which  arrive  at  the  right 
auricle  by  the  superior  and  inferior  vena  cava  respectively, 
thenceforth  mingle  in  this  cavity  of  the  heart,  and  passing 
into  the  right  ventricle,  go  byway  of  the  pulmonary  artery  to 
the  lungs,  and  through  these,  after  purification,  to  the  left 
auricle  and  ventricle,  to  be  distributed  over  the  body.  (See 
chapter  on  Circulation.) 

Development  of  the  Nervous  System. 

The  mode  in  which  the  rudimentary  structures  of  the  cere- 
bro-spinal  nervous  system  are  formed,  has  been  already  stated 
(p.  582).  The  dorsal  laminae,  the  inner  borders  of  which  close 
in  and  form  the  canal  of  the  spinal  cord,  seem  to  leave  a  fis- 
sure in  the  situation  of  the  medulla  oblongata.  Between  this 
and  the  most  anterior  extremity  of  the  canal,  three  vesicular 
enlargements,  the  vesicles  of  the  brain,  are  developed  (see  Fig. 
217),  and  from  these  again  are  developed  the  following  parts : 

From  the  anterior  primary  vesicle — the  optic  thalami,  cor- 
pora striata,  the  third  ventricle,  and  the  cerebral  hemispheres, 
together  with  some  other  parts  in  connection  with  those  above 
named,  as  the  corpus  callosum,  fornix,  &c. 

From  the  middle  primary  vesicle — the  corpora  quadrigem- 
ina  and  crura  cerebri,  with  the  aqueduct  of  Sylvius. 

From  the  posterior  primary  vesicle — the  cerebellum,  pons 
Varolii,  medulla  oblongata,  &c. 

Development  of  the  Organs  of  Sense. 

The  eye  is  in  part  developed  as  a  protruded  portion  of  the 
first  primary  cerebral  vesicle ;  while  passing  backwards,  and 


Diagram  of  development  of  the  lens.  ABC.  Different  stages  of  development. 
1.  Epidermic  layer.  2.  Thickening  of  this  layer.  3.  Crystalline  depression.  4. 
Primitive  ocular  vesicle,  its  anterior  part  pushed  back  by  the  crystalline  depression. 
5.  Posterior  part  of  the  primitive  ocular  vesicle,  forming  the  external  layer  of  the 
secondary  ocular  vesicle.  6.  Point  of  separation  between  the  lens  and  the  epidermic 
layer.  7.  Cavity  of  the  secondary  ocular  vesicle,  occupied  by  the  vitreous. 


604 


GENERATION  AND  DEVELOPMENT. 


pressing  on  the  front  of  this  process  or  primary  optic  vesicle,  is 
a  pouch  of  the  common  integument,  which  subsequently  be- 
comes a  shut  sac,  and  in  which  is  developed  the  lens  and  its 
capsule  (Fig.  236).  Subsequently  there  is  protruded  from 
below  upwards,  between  the  lens  in  front  and  the  primary 
optic  vesicle  behind,  another  process  or  pouch,  remaining  for 
some  time  imperfect  below,  and  called  the  secondary  optic  vesicle. 
The  deficiency  below  contracts  into  what  is  called  the  ocular 
cleft,  which  subsequently  becomes  entirely  obliterated.  In 
connection  with  the  primary  optic  vesicle  are  developed  the 


FIG.  237. 


op 


FIG.  236.— Diagrammatic  sketch  of  a  vertical  longitudinal  section  through  the  eye- 
ball of  a  human  foetus  of  fourweeks  (after  Kolliker)  !£!.  The  section  is  alittle  to  the 
side,  so  as  to  avoid  passing  through  the  ocular  cleft ;  c,  the  cuticle  where  it  becomes 
later  the  cornea;  I,  the  lens;  op,  optic  nerve  formed  by  the  pedicle  of  the  pri- 
mary optic  vesicle ;  vp,  primary  medullary  cavity  or  optic  vesicle ;  p,  the  pigment 
layer  of  the  choroid  coat  of  the  outer  wall ;  r,  the  inner  wall  forming  the  retina;  vs, 
secondary  optic  vesicle  containing  the  rudiment  of  the  vitreous  humor. 

FIG.  237. — Transverse  vertical  section  of  the  eyeball  of  a  human  embryo  of  four 
weeks  (from  Kolliker)  1  o  o.  The  anterior  half  of  the  section  is  represented :  pr,  the 
remains  of  the  cavity  of  the  primary  optic  vesicle  ;  p,  the  inner  part  of  the  outer 
layer  forming  the  choroidal  pigment;  r,  the  thickened  inner  part  giving  rise  to 
the  columnar  and  other  structures  of  the  retina;  v,  the  commencing  vitreous 
humor  within  the  secondary  optic  vesicle  ;  v',  the  ocular  cleft  through  which  the 
loop  of  the  central  bloodvessel,  a,  projects  from  below  ;  I,  the  lens  with  a  central 
cavity. 

retina  from  the  invaginated  portion,  and  the  pigmentary 
portion  of  the  choroid  in  connection  with  the  outer  part  (Fig. 
236).  In  the  secondary  optic  vesicle  the  vitreous  humor  is 
formed.  The  outer  walls  of  the  eyeball,  the  sclerotic  and 
cornea,  are  developed  from  the  tissues  immediately  around 
those  which  have  been  just  described. 

The  iris  is  formed  rather  late,  as  a  circular  septum  project- 


DEVELOPMENT    OF    THE    EYEBALL.  605 

ing  inwards,  from  the  fore  part  of  the  choroid,  between  the 
lens  and  the  cornea.  In  the  eye  of  the  foetus  of  Mammalia, 
the  pupil  is  closed  by  a  delicate  membrane,  the  membrana 
pupillaris,  which  forms  the  front  portion  of  a  highly  vascular 
membrane  that,  in  the  foetus,  surrounds  the  lens,  and  is  named 
the  membrana  capsulo-pupillaris.  It  is  supplied  with  blood  by 

FIG.  238. 


Bloodvessels  of  the  capsulo-pupillary  membrane  of  a  new-born  kitten,  magnified 
(from  Kolliker).  The  drawing  is  taken  from  a  preparation  injected  by  Tiersch,  and 
shows  in  the  central  part  the  convergence  of  the  network  of  vessels  in  the  pupil- 
lary membrane. 

a  branch  of  the  arteria  centralis  retince,  which,  passing  for- 
wards to  the  back  of  the  lens,  there  subdivides.  The  mem- 
brana capsulo-pupillaris  withers  and  disappears  in  the  human 
subject  a  short  time  before  birth. 

The  eyelids  of  the  human  subject  and  mammiferous  animals, 
like  those  of  birds,  are  first  developed  in  the  form  of  a  ring. 
They  then  extend  over  the  globe  of  the  eye  until  they  meet 
and  become  firmly  agglutinated  to  each  other.  But  before 
birth,  or  in  the  Garni vora  after  biHh,  they  again  separate. 

The  ear  likewise,  according  to  Huschke,  consists  of  a  part 
developed  from  within,  and  of  one  formed  externally.  The 
labyrinth  is  developed  upon  the  hollow  protruded  part  of  the 
brain  which  forms  the  auditory  nerve.  It  appears  first  in  the 
form  of  an  elongated  vesicle  at  the  hinder  part  of  the  head  of 
very  young  embryos  above  the  second  so-named  branchial 
cleft.  From  it  is  developed  a  second  vesicle,  the  rudiment  of 
the  cochlea,  the  convolutions  of  which  are  then  formed.  The 

51 


606 


GENERATION  AND  DEVELOPMENT. 


semicircular  canals  are  produced  as  diverticula  of  the  vestibule, 
which  terminate  by  again  communicating  with  the  same  cavity. 
The  Eustachian  tube,  the  cavity  of  the  tympanum,  and  the 
external  auditory  passage,  are  remains  of  the  first  branchial 
cleft.  The  membrana  tympani  divides  the  cavity  of  this  cleft 
into  an  internal  space,  the  tympanum,  and  the  external  meatus. 
The  mucous  membrane  of  the  mouth,  which  is  prolonged  in 
the  form  of  a  diverticulum  through  the  Eustachian  tube  into 
the  tympanum,  and  the  external  cutaneous  system,  come  into 
relation  with  each  other  at  this  point ;  the  two  membranes 
being  separated  only  by  the  proper  membrane  of  the  tym- 
panum. 

Development  of  the  Alimentary  Canal. 

The  alimentary  canal,  the  early  stage  of  whose  development 
has  been  already  referred  to  (p.  585),  is  at  first  a  uniform 
straight  tube,  which  gradually  becomes  divided  into  its  special 
parts,  stomach,  small  intestine,  and  large  intestine  (Fig.  239). 


Outlines  of  the  form  and  position  of  the  alimentary  canal  in  successive  stages  of 
its  development  (from  Quain).  A,  alimentary  canal,  &c.,  in  an  embryo  of  four 
weeks ;  B,  at  six  weeks  ;  C,  at  eight  weeks ;  D,  at  ten  weeks ;  I,  the  primitive  lungs 
connected  with  the  pharynx ;  s,  the  stomach  ;  d,  duodenum ;  i,  the  small  intestine  ; 
i',  the  large ;  c,  the  caecum  and  vermiform  appendage  ;  r,  the  rectum  ;  cl,  in  A,  the 
cloaca ;  a,  in  B,  the  anus,  distinct  from  si,  the  sinus  uro-genitalis ;  v,  the  yelk-sac ; 
vi,  the  vitello-intestinal  duct ;  u,  the  urinary  bladder  and  urachus  leading  to  the 
allantois;  g,  genital  ducts. 


DEVELOPMENT    OF    THE     LIVER. 


607 


The  stomach  originally  has  the  same  direction  as  the  rest  of 
the  canal ;  its  cardiac  extremity  being  superior,  its  pylorus  in- 
ferior. The  changes  of  position  which  the  alimentary  canal 
undergoes  may  be  readily  gathered  from  the  accompanying 
figures. 

The  principal  glands  in  connection  with  the  intestinal  canal 
are  the  salivary,  pancreas,  and  the  liver.  In  Mammalia,  each 
salivary  gland  first  appears  as  a  simple  canal  with  bud-like 
processes  (Fig.  240),  lying  in  a  gelatinous  nidus  or  blastema, 
and  communicating  with  the  cavity  of  the  mouth.  As  the 
development  of  the  gland  advances,  the  canal  becomes  more 
and  more  rainitied,  increasing  at  the  expense  of  the  blastema 

FIG.  241. 


FIG.  240. 


FIG.  240. — First  appearaace  of  the  parotid  gland  in  the  embryo  of  a  sheep. 
FIG.  241. — Lobules  of  the  parotid,  with  the  salivary  ducts,  in  the  embryo  of  the 
sheep,  at  a  more  advanced  stage. 

in  which  it  is  still  inclosed.  The  branches  or  salivary  ducts 
constitute  an  independent  system  of  closed  tubes  (Fig.  241). 
The  pancreas  is  developed  exactly  as  the  salivary  glands. 

The  liver  in  the  embryo  of  the  bird  is  developed  by  the 
protrusion,  as  it  were,  of  a  part  of  the  walls  of  the  intestinal 
canal,  in  the  form  of  two  conical  hollow  branches,  which  em- 
brace the  common  venous  stem  (Fig.  242).  The  outer  part  of 
these  cones  involves  the  omphalo-meseuteric  vein,  which  breaks 
up  in  its  interior  into  a  plexus  of  capillaries,  ending  in  venous 


608         GENERATION     AND     DEVELOPMENT. 

trunks  for  the  conveyance  of  the  blood  to  the  heart.  The 
inner  portion  of  the  cones  forms  the  cellular  structure  of  the 
organ  into  which  the  bloodvessels  extend,  and  in  which  they 

FIG.  242. 


Rudiments  of  the  liver  on  th  '  intestine  of  a  chick  at  the  fifth  day  of  incubation, 
o,  heart;  b,  intestine  ;  c,  diverticulura  of  the  intestine  on  which  the  liver  (d)  is  de- 
veloped; e,  part  of  the  mucous  layer  of  the  germinal  membrane. 

are,  with  the  ducts,  gradually  developed.    The  gall-bladder  is 
developed  as  a  diverticulum  from  the  hepatic  duct. 

Development  of  the  Respiratory  Apparatus. 

The  lungs,  at  their  first  development,  appear  as  small  tuber- 
cles, or  diverticula  from  the  abdominal  surface  of  the  oesoph- 

FIG.  243. 
A  B  C 


I 


u  • 

Illustrating  the  development  of  the  respiratory  organs.  A,  is  the  oesophagus  of  a 
chick  on  the  fourth  day  of  incubation,  with  the  rudiments  of  the  trachea  on  the 
lung  of  the  left  side,  viewed  laterally:  1,  the  inferior  wall  of  the  resophagus;  2,  the 
upper  wall  of  the  same  tube;  3,  the  rudimentary  lung;  4,  the  stomach.  B,  is  the 
same  object  seen  from  below,  so  that  both  lungs  are  visible,  c,  shows  the  tongue  and 
respiratory  organs  of  the  embryo  of  a  horse:  1,  the  tongue;  2,  the  larynx;  3,  the 
trachea;  4,  the  lungs  viewed  from  the  upper  side.  (After  Rathke.) 

agus.  They  are  united  at  the  anterior  part  of  their  circum- 
ference ;  and  here  a  pedicle  is  formed  which  becomes  elongated 
into  the  trachea  (see  Fig.  243,  A,  B).  Soon  afterwards,  the 


THE    WOLFFIAN    BODIES.  609 

lung  is  seen  to  consist  of  a  mass  of  csecal  tubes  issuing  from 
the  branches  of  the  trachea.  (Fig.  243,  c.)  The  diaphragm 
is  early  developed. 

The  Wolffian  Bodies,  Urinary  Apparatus,  and  Sexual  Organs. 

The  Wolffian  bodies  are  organs  peculiar  to  the  embryonic 
state,  and  may  be  regarded  as  temporary,  rather  than  rudi- 
mental,  kidneys;  for  although  they  seem  to  discharge  the 
functions  of  these  latter  organs,  they  are  not  developed  into 
them.  They  probably  bear  the  same  relation  to  the  persistent 
kidneys  that  the  branchiae  of  Amphibia  do  to  the  lungs  which 
succeed  them. 

In  Mammalia,  the  Wolffian  bodies  (Fig.  244,  W)  are  bean- 
shaped,  and  are  composed  of  transverse  csecal  canals,  united 
by  an  excretory  duct  (to),  which  leads  from  the  lower  extrem- 
ity of  the  organ  to  the  sinus  urogenitalis  of  the  foetus  (Fig. 
244,  ug\  The  kidneys  (r)  and  suprarenal  capsules  (sr)  are 
developed  behind  them.  Their  size  is  at  first  so  great  that  they 
entirely  conceal  the  kidneys ;  but  in  proportion  as  the  latter 
bodies  increase  in  size,  they  grow  relatively  smaller,  and  come 
to  be  placed  more  inferiorly.  At  length,  towards  the  end  of 
foetal  life,  only  an  atrophied  remnant  of  them  is  left.  Their 
ducts,  in  the  male,  are  ultimately  developed  to  form  the  vas 
deferens  and  ejaculatory  duct  of  each  side ;  the  vesiculse  semi- 
nales  forming  diverticula  from  their  lower  part.  In  the  female, 
the  ducts  of  the  Wolffian  bodies  disappear. 

The  testicles  or  ovaries  are  formed  independently  at  the 
internal  excavated  border  of  these  organs;  and  at  first  it  is  not 

Cible  to  say  which  of  them — the  testicle  or  ovary — the  new 
lation  is  to  become.  Gradually,  however,  the  special  char- 
acters belonging  to  one  of  them  are  developed ;  and  in  either 
case  the  organ  soon  begins  to  assume  a  relatively  lower  posi- 
tion in  the  body ;  the  ovaries  being  ultimately  placed  in  the 
pelvis ;  while  towards  the  end  of  foetal  existence  the  testicles 
descend  into  the  scrotum,  the  testicle  entering  the  internal 
inguinal  ring  in  the  seventh  month  of  foetal  life,  and  complet- 
ing its  descent  through  the  inguinal  canal  and  external  ring 
into  the  scrotum  by  the  end  of  the  eighth  month.  A  pouch  of 
peritoneum,  the  processus  vaginalis,  precedes  it  in  its  descent, 
and  ultimately  forms  the  tunica  vaginalis  or  serous  covering 
of  the  organ ;  the  communication  between  the  tunica  vaginalis 
and  the  cavity  of  the  peritoneum  being  closed  only  a  short 
time  before  birth.  In  its  descent,  the  testicle  or  ovary  of 
course  retains  the  bloodvessels,  nerves,  and  lymphatics,  which 
were  supplied  to  it  while  in  the  lumbar  region,  and  which  are 


610         GENERATION     AND     DEVELOPMENT. 

compelled  to  follow  it,  so  to  speak,  as  it  assumes  a  lower  posi- 
tion in  the  body.  Hence  the  explanation  of  the  otherwise 
strange  fact  of  the  origin  of  these  parts  at  so  considerable  a 
distance  from  the  organ  to  which  they  are  distributed. 

The  means  by  which  the  descent  of  the  testicles  into  the 
scrotum  is  effected  are  not  fully  and  exactly  known.  It  was 
formerly  believed  that  a  membranous  and  partly  muscular 
cord,  called  the  gubernaculum  testis,  which  extends  while  the 
testicle  is  yet  high  in  the  abdomen,  from  its  lower  part, 
through  the  abdominal  wall  (in  the  situation  of  the  inguinal 
canal)  to  the  front  of  the  pubes  and  lower  part  of  the  scrotum, 
was  the  agent  by  the  contraction  of  which  the  descent  was 
effected.  It  is  now  generally  believed,  however,  that  such  is 
not  the  case ;  and  that  the  descent  of  the  testicle  and  ovary  is 
rather  the  result  of  a  general  process  of  development  in  these 
and  neighboring  parts,  the  tendency  of  which  is  to  produce 
this  change  in  the  relative  position  of  these  organs.  In  other 
words,  the  descent  is  not  the  result  of  a  mere  mechanical 
action,  by  which  the  organ  is  dragged  down  to  a  lower  position, 
but  rather  one  change  out  of  many  which  attend  the  gradual 
development  and  rearrangement  of  these  organs.  It  may  be 
repeated,  however,  that  the  details  of  the  process  by  which  the 
descent  of  the  testicle  into  the  scrotum  is  effected  are  not 
accurately  known. 

The  homologue,  in  the  female,  of  the  gubernaculum  testis, 
is  a  structure  called  the  round  ligament  of  the  uterus,  which  ex- 
tends through  the  inguinal  canal,  from  the  outer  and  upper 
part  of  the  uterus  to  the  subcutaneous  tissue  in  front  of  the 
symphysis  pubis. 

At  a  very  early  stage  of  fostal  life,  the  efferent  ducts  of  the 
Wolffian  bodies  of  the  kidneys  and  of  the  ovaries  or  testes, 
open  into  a  receptacle  formed  by  the  lower  end  of  the  allan- 
tois,  or  rudimentary  bladder ;  and  as  this  communicates  with 
the  lower  extremity  of  the  intestine,  there  is  for  the  time,  a 
common  receptacle  or  cloaca  for  all  these  parts,  which  opens  to 
the  exterior  of  the  body  through  a  part  corresponding  with 
the  future  anus.  In  a  short  time,  however,  the  intestinal  por- 
tion of  the  cloaca  is  cut  off  from  that  which  belongs  to  the 
urinary  and  generative  organs ;  a  separate  passage  or  canal  to 
the  exterior  of  the  body,  belonging  to  these  parts,  being  called 
the  sinus  urogenitalis.  Subsequently,  this  canal  is  divided,  by 
a  process  of  division  extending  from  before  backwards  or  from 
above  downwards,  into  a  "  pars  urinaria"  and  a  "  pars  genita- 
lis."  The  former,  continuous  with  the  urachus  (p.  587),  is 
converted  into  the  urinary  bladder. 

The  Fallopian  tubes,  the  uterus,  and  the  vagina  are  de- 


THE    MULLERIAN     DUCTS. 


611 


veloped  from  two  threads  of  blastema,  called  the  Mullerian 
ducts  (Fig.  244,  w),  which  appear  in  front  of  the  Wolffian 
bodies  at  about  the  time  that  these  begin  to  change  their  rela- 
tive position  to  neighboring  parts,  and  to  decrease  in  size. 
The  two  Mullerian  ducts  are  united  below  into  a  single  cord, 
called,  the  genital  cord,  and,  from  this  are  developed  the 
vagina,  as  well  as  the  cervix  and  the  lower  portion  of  the  body 
of  the  uterus ;  while  the  ununited  portion  of  the  duct  on  each 
side  forms  the  upper  part  of  the  uterus,  and  the  Fallopian 
tube.  In  certain  cases  of  arrested  or  abnormal  development, 
these  portions  of  the  Mullerian  ducts  may  not  become  fused 


FIG.  244. 


Diagram  of  the  Wolffian  bodies,  Mullerian  ducts  and  adjacent  parts  previous  to 
sexual  distinction,  as  seen  from  before  (from  Quain).  sr,  the  suprarenal  bodies; 
r,  the  kidneys  ;  ol,  common  blastema  of  ovaries  or  testicles ;  W,  Wolffian  bodies ;  w, 
Wolffian  ducts:  m,  m,  Miillerian  ducts;  gc,  genital  cord;  ug,  sinus  urogenitalis ;  i, 
intestine ;  cl,  cloaca. 

together  at  their  lower  extremities,  and  there  is  left  a  cleft  or 
horned  condition  of  the  upper  part  of  the  uterus,  resembling 
a  condition  which  is  permanent  in  certain  of  the  lower  ani- 
mals. 


612 


GENERATION  AND  DEVELOPMENT. 


In  the  male,  the  Mullerian  ducts  have  no  special  function, 
and  are  but  slightly  developed :  the  small  prostatic  pouch,  or 
sinus  pocularis,  forms  the  atrophied  remnant  of  the  genital 
cord,  and  is,  of  course,  therefore,  the  homologue,  in  the  male, 
of  the  vagina  and  uterus  in  the  female. 


FIG.  245. 


Urinary  and  generative  organs  of  a  human  female  embryo,  measuring  3%  inches 
in  length.  A,  general  view  of  these  parts  ;  1,  suprarenal  capsules  ;  2,  kidneys  ;  3, 
ovary  ;  4,  Fallopian  tuba ;  5,  uterus  ;  6,  intestine  ;  7,  the  bladder.  B,  Bladder  and 
generative  organs  of  the  same  embryo  viewed  from  the  side  ;  a,  the  urinary  bladder 
(at  the  upper  part  is  a  portion  of  the  urachus) ;  2,  urethra  ;  3,  uterus  (with  two  cor- 
nua) ;  4,  vagina ;  5,  part  as  yet  common  to  the  vagina  and  urethra  ;  6,  common  ori- 
fice of  the  urinary  and  generative  organs  ;  7,  the  clitoris,  c,  Internal  generative  or- 
gans of  the  same  embryo  ;  1,  the  uterus  ;  2,  the  round  ligaments  ;  3,  the  Fallopian 
tubes  (formed  by  the  Mullerian  duets) ;  4,  the  ovaries ;  5,  the  remains  of  the  Wolffian 
bodies.  r>,  External  generative  organs  of  the  same  embryo  ;  1,  the  labia  majora  ;  2 
the  nymphse  ;  3,  the  clitoris.  After  Miiller. 


The  external  parts  of  generation  are  at  first  the  same  in 
both  sexes.  The  opening  of  the  genito-urinary  apparatus  is, 
in  both  sexes,  bounded  by  two  folds  of  skin,  whilst  in  front  of 
it  there  is  formed  a  penis-like  body  surmounted  by  a  glans, 
and  cleft  or  furrowed  along  its  under  surface.  The  borders  of 


THE    MAMMARY    GLANDS.  613 

the  furrow  diverge  posteriorly,  running  at  the  sides  of  the 
genito-urinary  orifice  internally  to  the  cutaneous  folds  just 
mentioned  (see  Fig.  245,  B,  D).  In  the  female,  this  body  be- 
coming retracted,  forms  the  clitoris,  and  the  margins  of  the 
furrow  on  its  under  surface  are  converted  into  the  nymphse,  or 
labia  minora,  the  labia  majora  pudendse  being  constituted  by 
the  great  cutaneous  folds.  In  the  male  foetus,  the  margins  of 
the  furrow  at  the  under  surface  of  the  penis  unite  at  about  the 
fourteenth  week,  and  form  that  part  of  the  urethra  which  is 
included  in  the  penis.  The  large  cutaneous  folds  form  the 
scrotum,  and  at  a  later  period,  namely,  in  the  eighth  month 
of  development,  receive  the  testicles,  which  descend  into  them 
from  the  abdominal  cavity.  Sometimes  the  urethra  is  not 
closed,  and  the  deformity  called  hypospadias  then  results.  The 
appearance  of  hermaphroditism  may,  in  these  cases,  be  in- 
creased by  the  retention  of  the  testes  within  the  abdomen. 

The  Mammary  Glands. 

The  mammary  glands,  which  may  be  considered  as  organs 
superadded  to  the  reproductive  system  in  man  and  other  mem- 
bers of  the  class  (Mammalia)  which  derives  its  name  from 
them,  are,  in  the  essential  details  of  their  structure,  very  simi- 
lar to  other  compound  glands,  as  the  pancreas  and  salivary 
glands ;  that  is  to  say,  they  are  composed  of  larger  divisions 
or  lobes,  and  these  are  again  divisible  into  lobules, — the  lob- 
ules being  composed  of  the  follicular  extremities  of  ducts, 
lined  by  glandular  epithelium.  The  lobes  and  lobules  are 
bound  together  by  areolar  tissue ;  while,  penetrating  between 
the  lobes,  and  covering  the  general  surface  of  the  gland,  with 
the  exception  of  the  nipple,  is  a  considerable  quantity  of  yellow 
fat,  itself  lobulated  by  sheaths  and  processes  of  tough  areolar 
tissue  (Fig.  246)  connected  both  with  the  skin  in  front  and 
the  gland  behind  ;  the  same  bond  of  connection  extending  also 
from  the  under  surface  of  the  gland  to  the  sheathing  connec- 
tive tissue  of  the  great  pectoral  muscle  on  which  it  lies.  The 
main  ducts  of  the  gland,  fifteen  to  twenty  in  number,  called  the 
lactiferous  or  galactophorous  ducts,  are  formed  by  the  union  of 
the  smaller  ducts,  and  open  by  small  separate  orifices  through 
the  nipple.  Just  before  they  enter  the  base  of  the  nipple,  these 
ducts  are  dilated  (6,  Fig.  246) ;  and,  during  lactation,  the  period 
of  active  secretion  by  the  gland,  they  form  reservoirs  for  the 
milk,  which  collects  in  them  and  distends  them.  The  walls  of 
the  gland-ducts  are  formed  of  areolar  and  elastic  tissue,  and 
are  lined,  internally  by  a  fine  mucous  membrane,  the  surface 
of  which  is  covered  by  squamous  or  spheroidal  epithelium. 

52 


614 


GENERATION  AND  DEVELOPMENT. 


The  nipple,  which  contains  the  terminations  of  the  lactifer- 
ous ducts,  is  composed  also  of  areolar  tissue,  and  contains  un- 
striped  muscular  fibres.  Bloodvessels  are  also  freely  supplied 


FIG.  246. 


Dissection  of  the  lower  half  of  the  female  mamma  during  the  period  of  lactation 
(from  Luschka).  %. — In  the  left-hand  side  of  the  dissected  part  the  glandular  lobes 
are  exposed  and  partially  unravelled;  and  on  the  right-hand  side,  the  glandular 
substance  has  been  removed  to  show  the  reticular  loculi  of  the  connective  tissue  in 
which  the  glandular  lobules  are  placed :  1,  upper  part  of  the  mammilla  or  nipple ; 
2,  areola ;  3,  subcutaneous  masses  of  fat ;  4,  reticular  loculi  of  the  connective  tissue 
which  support  the  glandular  substance  and  contain  the  fatty  masses  ;  5,  one  of  three 
lactiferous  ducts  shown  passing  towards  the  mammilla  where  they  open  ;  6,  one  of 
the  sinus  lactei  or  reservoirs ;  7,  some  of  the  glandular  lobules  which  have  been  un- 
ravelled ;  7',  others  massed  together. 


to  it,  so  as  to  give  it  a  species  of  erectile  structure.  On  its 
surface  are  very  sensitive  papillae ;  and  around  it  is  a  small 
area  or  areola  of  pink  or  dark-tinted  skin,  on  which  are  to  be 
seen  small  projections  formed  by  minute  secreting  glands. 

Bloodvessels,  nerves,  and  lymphatics  are  plentifully  supplied 
to  the  mammary  glands ;  the  calibre  of  the  bloodvessels,  as 
well  as  the  size  of  the  glands,  varying  very  greatly  under  cer- 
tain conditions,  especially  those  of  pregnancy  and  lactation. 

The  secretion  of  milk,  which  under  ordinary  healthy  cir- 


COMPOSITION    OF    MILK. 


615 


cumstances  only  occurs  after  parturition,  if  we  except  the 
slight  secretion  which  takes  place  in  the  latter  months  of  preg- 
nancy, is  effected  by  the  epithelial  cells  lining  the  ultimate 
follicles  of  the  mammary  gland.  The  process  does  not  differ 
from  secretion  in  glands  generally  (see  p.  321),  and  need  not 
here  be  particularly  described. 

Under  the  microscope,  milk  is  found  to  contain  a  number 
of  globules  of  various   size  (Fig.  247),  the  majority  about 


»$*• 

Microscopic  appearance  of  human  milk  with  an  intermixture  of  colostric 
corpuscles. 


an  nc  n  diameter.  They  are  composed  of  oily 
matter,  probably  coated  by  a  fine  layer  of  albuminous  material, 
and  are  called  milk-globules;  while,  accompanying  these,  are 
numerous  minute  particles,  both  oily  and  albuminous,  which 
exhibit  ordinary  molecular  movements.  The  milk  which  is 
secreted  in  the  first  few  days  after  parturition,  and  which  is 
called  the  colostrum,  differs  from  ordinary  milk  in  containing 
a  larger  quantity  of  solid  matter ;  and  under  the  microscope 
are  to  be  seen  certain  granular  masses  called  colostrum-cor- 
puscles. These,  which  appear  to  be  small  masses  of  albumin- 
ous and  oily  matter,  are  probably  secreting  cells  of  the  gland, 
either  in  a  state  of  fatty  degeneration,  or,  as  Dr.  Gedge  re- 
marks, old  cells  which  in  their  attempts  at  secretion  under  the 
new  circumstances  of  active  need  of  milk,  are  filled  with  oily 
matter ;  which,  however,  being  unable  to  discharge,  they  are 
themselves  shed  bodily  to  make  room  for  their  successors. 

The  specific  gravity  of  human  milk  is  about  1030.     Its 
chemical  composition  has  been  already  mentioned  (p.  200). 


LIST  OF  WORKS  REFERRED  TO. 


PAGE 

23.  SMEE.  Proc.  K.  Soc.     1863. 

25.  PREPONDERANCE  OF  MAGNESIA  OVER  LIME  IN  JUICE  or  MUS- 
CLES.    Liebig.     Chemistry  of  Food.     1847. 
56.   BERNARD.     Le9ons  de  Phys.  Experimentale.     Paris.  1859. 
"     SAVORY.    On  the  Relative  Temperature  of  Arterial  and  Venous 

Blood.     Pamphlet. 

BERNARD.     The  Medical  Times  and  Gazette,  April  21,  1860. 
BARRUEL.    Annales  d'Hygiene  Publique  et  de  Medecine  Legale. 
VALENTIN.     Repert.  f.  Anat.  und  Phys.     Bd.  iii,  p.  281. 
BLAKE.     Prof.  Dunglison  :  Physiol.     7th  ed.,  vol.  ii,  p.  102. 
LEHMANN.     Physiolog.  Chem.     Cavend.  Soc.  Edit  ,  vol.  ii,  p. 

269. 

"     BERNARD.     Le9ons.     1859.     T.  i,  p.  419 

61.  ALEXANDER  SCHMIDT.  Archiv.  fiir  Anatomic,  Physiologie, 
&c.  By  Reichert  and  Du  Bois-Raymond,  being  a  continu- 
ation of  Neil's,  Meckel's,  and  Job.  Miiller's  Archiv.  Leip- 
zig, 1861,  p.  545;  and  1862,  pp.  428  and  583. 

"  ANDREW  BUCHANAN.  Proceedings  of  the  Glasgow  Philosophi- 
cal Society.  Feb.,  1845. 

64.  GULLIVER.     London  Medical  Gazette.     Vol.  xli.  p    1087. 
72.  WHARTON  JONES.     Philosophical  Transactions.     1846. 

75.  LEHMANN.    Dr.  Geo.  E.  Day:  Chemistry,  in  Relation  to  Physi- 

ology and  Medicine,  p.  216.     1860.     Bailliere. 

"  ENDERLIN.  Annalen  der  Chemie  und  Pharmacie.  Von  Liebig 
und  Wohler.  1844. 

76.  DENIS.    F.  Simon:  Animal  Chemistry.    Translated  by  Dr.  Day 

for  the  Sydenham  Soc. 

77.  JOHN  DAVY.     Anat.  and  Phys.  Researches.     Vol.  ii,  p.  28. 

"     POLLI.     Researches  and  Experiments  upon  the  Human  Blood. 

Noticed  in  the  Medico-Chirurgical  Review,  Oct.,  1847. 
"     PROF.  STOKES.     Proceedings  of  the  Royal  Society.     1863-4. 
97.  HARVEY'S  WORKS.     Syd.  Soc   Edition.     1847,  p.  31. 
103.  W.  S.  SAVORY.    Observations  on  the  Structure  and  Connection 

of  the  Valves  of  the  Human  Heart.     Pamphlet,  1851. 
106.  VALENTIN.     De  Functionibus  Nervorum  Cerebralium  et  Nervi 

Sympathetic!.     Berne,  1839.     Bd.  i,  p.  427. 
J07.  DR.    REID.       The   Cyclopaedia   of  Anatomv   and   Physiology. 

Edited  by  Dr.  Todd.     Vol.  ii,  p.  (i06. 

"  KURSCHNER.  R.  Wagner:  Handworterbuch  der  Physiologie. 
Braunschweig.  Art.  Herzthatigkeit. 

108.  MARKY.    Physiologic  Medicale  de  la  Circulation  du  Sang.    1863. 

109.  DR.  GUY.     Guy's  Hospital  Reports.     Nos.  vi  and  vii. 

110.  VALENTIN.     Lebrbuch  der  Physiologie  des  Menschen.     Bd.  i, 

p.  415,  &(.'.     Braunschweig,  1844. 


618  LIST    OF    AUTHORS. 


110.  OESTERREICHER.       Lehre   vom    Kreislauf   des   Blutes,   p.    33. 
Nuremberg,  1826. 

112.  GANGLIA.  IN  THE  SUBSTANCE  OF  THE  HEART.     Remak.     Medi- 

cinische  Zeitung  des  Vereins  fiir  Heilkunde  in  Preussen. 
No.  ii,  1840. 

"  VOLKMANN.  Miiller  :  Archiv.  fiir  Anatomie,  Physiologie,  und 
wissenschaftliche  Medecin.  1844,  p.  424.  Berlin. 

"     DR.  R.  LEE.     Proceedings  of  the  Royal  Society.     1847. 

«'     London  Medical  Gazette.     Vol.  xlv,  p.  224. 

u  PAGET.  Reports  on  the  Use  of  the  Microscope,  and  on  the  Prog- 
ress of  Human  Anatomy  and  Physiology,  in  the  British  and 
Foreign  Medical  Review.  1844-5,  p.  13. 

113.  PAGET.     Proceedings  of  the  Royal  Society.     May,  1857. 

114.  SHARPKY.     Edinburgh  Medical   and   Surgical  Journal.     Vol. 

Ixiii,  p.  10. 

119.  JOHN  HUNTER.     Works  of,  Edited  by  Mr.  Palmer.     Vol.  iii, 

p.  157.     London,  Longmans,  1835. 

120.  E.  H.  WEBER.     Miiller:  Archiv.  fiir  Anatomie,  Physiologie, 

und  wissenschaftliche  Medecin.     1847,  p.  232.     Berlin. 
"     PROF.    KOLLIKKR.       British  and   Foreign   Medico-Chirurgical 

Review.     July,  1850,  p.  241. 

122.  W.  S.  SAVORY.     On  the  Shape  of  Transverse  Wounds  of  Blood- 
vessels.    Pamphlet,  1859. 

129.  THOMAS  YOUNG.     Philosophical  Transactions.     Vol.  xcix. 
11     POISEUILLE.     Magendie :  Journ.  de  Phys.     T.  viii,  p.  272. 

130.  POISEUILLE.       Comptes   Rendus   des    Stances   de   1'Academie 

Royale  des  Sciences  de  Paris.     1860,  p.  238. 

131.  LUDWIG.     Mailer:  Archiv.,  &c.     1847,  p.  242. 

132.  For  instances  of  occasional  direct  communications  between  arte- 

ries and  veins  see  Suchet :  Bulletin  de  1'Acad.  de  Med.  T. 
xxvi,  p.  825. 

136.  MARSHALL  HALL.     Edinburgh  Med.  and  Surg.  Journ.     1843. 

137.  HALES.     Statist.  Essays.     Vol.  ii.     London,  1740. 

u  WEBER.  Miiller:  Archiv.  fiir  Anat.,  Ph3*s.,  und  wissenschaft- 
liche Medecin.  Berlin,  1838,  p.  450. 

"  VALENTIN.  Lehrbuch  der  Phys.  des  Menschen.  Braunschweig, 
1844,  Vol.  i,  p.  4G8. 

138.  BURDON  SANDERSON.     Holmes's  System  of  Surgery.     Vol.  v. 

Art.  Inflammation.     1871 

"     WALLER.     Philosophical  Magazine.     Vol.  xxix,  1846. 
143.  MOGK.     Henle  and  Pfeufer  :  Zeitschrift  fiir  Rationelle  Medizin. 

Heidelberg,  1845,  p.  33. 
11     VALENTIN.    Lehrbuch  der  Phys.  des  Menschen.    Braunschweig. 

1844,  p.  477. 

145.  WHARTON  JONES.     Philos.  Trans.  1852 

"  LUDWIG.  Miiller:  Archiv.  fiir  Anat.,  Phvs.,  und  wissenschaft- 
liche Medecin.  Berlin,  1847,  p.  242.  " 

146.  VALENTIN.    Lehrbuch  der  Phys.  des  Menschen.    Braunschweig, 

1844,  p.  478. 

"  LUDWIG.  Miiller:  Archiv.  fiir  Anat.,  Phys.,  und  wissenschaft- 
liohe  Medecin.  Berlin,  1847,  p.  242.  * 

147.  BURDON  SANDERSON.     Proc.  of  the  Royal  Soc.     1867. 

148.  POISEUILLE.    Annales  des  Sciences  Naturelle*:  Zoologie.    1843. 
"     J.  BLAKE.     Edinburgh   Medical  and  Surgical   Journal.     Oct., 

1841. 


LIST    OF    AUTHORS.  619 


^ 

*152.  KELLIE.     London  Med.  Gaz      May,  1843. 
"     BURROWS.     Disorders  of  the  Cerebral  Circulation.     1846. 

153.  GUENTHER.     Meckel:    Archiv.   fiir.   Anat.    und    Phys.      1828, 

p.  364. 

154.  KOLLIKER.    Das  anatomische  und  physiologische  Verhalten  der 

cavernosen  Korper  der  Sexualorgane. 
"     KOBELT.     Spallanzani  :  Versuch  iiber  das  Verdauungsgesch'aft. 

Leipzig,  1785. 

"     LE  GROS  CLARK.     London  Med.  Gaz.     Vol.  xviii,  p.  437. 
"     KRAUSE      Mtiller  :  Archiv.  fiir  Anat  ,  Phys  ,  und  wissenschaft- 

liche  Medeciri.     Berlin,  1837 

163.  MM.  BEAU  ET  MAISSIAT.     Archives  Generales  de  Medecine. 

1842-3. 

164.  Note,  HUTCHINSON.     Trans  of  the  Royal  Med.-Chir.  Soc.    Vol. 

xxix. 

166.  BOURGERY.    Archives  Generales  de  Medecine.     1843. 
"     E.  SMITH.     Carpenter  :  Princ.  of  Human  Phys.     Edited  by  H. 

Power.     1864. 
•  "     HUTCHINSON.     Trans,  of  the  Royal  Med.-Chir.  .Soc.    Vol.  xxix. 

170.  Rep.  of  Med.-Chir.  Committee.    Trans,  of  the  Royal  Med  -Chir. 

Soc.     1862. 

171.  RADCLYFFE  HALL.     On  the  Action  of  the  Muscular  Coat  of  the 

Bronchial  Tubes.     Pamphlet.  1851. 
"     GAIRDNER.     Monthly   Journ.    of   Med.    Science.     Edinburgh. 

May,  1851. 
u     C.  J.  B.  WILLIAMS.     Carpenter:  Princ.  of  Human  Phys.     3d 

ed.,  p.  588. 
"     VOLKMANN.     R.Wagner:   Handworterbuch  der  Phys.     Braun- 

schweig     Art.  Nervenphysiologie,  p.  586. 

173.  VALENTIN  UND  BRUNNER.    Lehrbuch  der  Phys.  des  Menschen. 

Braunschweig,  1844.     Vol.  i,  p.  547. 

174.  ED.  SMITH.     Philosoph  Trans.     1859. 

';     ANDRAL  ET  GAVARRET.     Recherches  sur  la  quantite  d'Acide 

Carbonique  exhale  par  le  Poumon.     Paris,  1843. 
"     VIERORDT.     Phys.  des  Athmens.     1845. 

175.  LETTELLIER.     Annales  de  Chimie  et  de  Physique.     1845. 
"     ED.  SMITH      Philosoph    Trans.     1859. 

"     ALLEN  AND  PEPYS.     Philos.  Trans.     1808-9. 

176.  LEHMANN.     Dr.  Geo.  E.  Day:  Chemistry  in  Relation  to  Phys. 

and  Med.     1860.     Balliere.     p.  469. 
"     ED.  SMITH.     Philosoph.  Trans.     1859 

177.  VALENTIN  UND  BRUNNER.    Lehrbuch  der  Phys.  des  Menschen. 

Braunschweig,  1844.     Bd.  i. 
"     BENCE  JONES.     Chem.  Gaz.     April,  1851. 
"     BENCE  JONES.     The  Med.  Times.    August  30th,  1851. 
"     REQNAULT  AND  REISET.    Brit,  and  For.  Med.-Chir.  Rev.    July, 

1850,  p   252. 

178.  LIEBIG.    Animal  Chem.    Trans,  by  Dr.  Gregory.    3d  ed.,  p.  184. 

179.  RANSOME.     Cambr.  Jour,  of  Anat  and  Phys.,  May,  1870. 
187.  ECCLES      London  Med.  Gaz.     Vol.  xliv,  p.  657. 

"     Report  of  Med.-Chir.  Committee.     Trans,  of  the  Royal  Med.- 

Chirur.  Soc.,  1862. 
189.  MARSHALL  HALL.     The  Cyclopaedia  of  Anat.  and  Phys.     Ed. 

by  Dr.  Todd.     Vol.  ii,  p.  771. 
"     WUNDERLICH.     Med.  Thermometry.    Transl.  by  B.  Woodman, 

M.D.     New  Syd.  Soc.  Trans.     1871. 


620  LIST    OF    AUTHORS. 

PAGK 

190.  OGLE.     St.  George's  Hosp.  Keports.     Vol.  i. 

191.  GEE.     Gulstonian  Lectures.     Brit.  Med.  Jour.,  1871. 
"     DAVY.     Proceedings  of  the  Royal  Soc.,  June,  1845. 

"     TIEDEMANN  AND   RuDOLPHl.     Tiedemann :    Phys.,  translated 
bv  Gully  and  Lane,  p.  234. 

192.  JOHN"  HUNTER.     Works  of,  Ed.  by  Mr.  Palmer.     1835.     Vol. 

iii,  p.  16,  and  vol.  iv,  p.  131,  et  seq. 
194.  NEWPORT.     Philosoph.  Trans.     1837. 
196.  C.  JAMES.     Gazette  Medicale  de  Paris,  April,  1844. 
198.  EARLE.     Trans,  of  the  Royal  Med.-Chir.  Soc.     Vol.  vii,  p.  173. 
201.  CHOSSAT.     Gaz.  He'd,  de  Paris,  Oct.,  1843 

"     LETTELLIER.     Annales  de  Chimie  et  de  Physique.     1844. 
210.    WRIGHT.     The  Lancet.     1842-3. 

212.  OWEN.     Dr.  Carpenter  :  Princ.  of  Human  Phys.,  5th  ed.     1855, 

p.  76,  note. 

213.  BERNARD.     The  Med.  Times  and  Gaz.,  July  7th,  1860. 
218.   BRINTON.     On  Food  and  its  Digestion,  Churchill,  1861. 

220.  BEAUMONT.    Experiments  and  Observations  on  the  Gastric  Juice, 

and  the  Phys.  of  Digestion,  by  W.  Beaumont.     US,  1834.- 
Reprinted,  with  notes,  by  Dr  A.  Combe.     Edinburgh,  1838. 

"     BLONDLOT.     Traite"  Analytiquede  Digestion.     8vo.,  Paris,  1844. 

"     BERNARD.     Gaz.  Med   de  Paris,  June,  1844. 

221.  Chem   in  relation  to  Phys.  and  Mod.  by  Dr.  G.  E.  Day.     1860. 

Bailliere.     p.  158. 

"     GEO.  E.  DAY.     Chem.,  &c.,  p.  159. 

223.  BEAUMONT.  Experiments  and  Observations  on  the  Gastric  Juice, 
and  the  Phys.  of  Digestion,  by  W.  Beaumont.  U.  S.,  1834. 
Reprinted,  with  notes,  by  Dr.  A.  Combe.  Edinburgh,  1838, 
p.  120. 

227.  GOSSE.     Spallanzani :    Versuch   iiber  das  Verdauungsgeschaft. 

Leipzig,  1785. 

228.  RAWITZ.   Weber :  die  Einfachen  Nahrungsmittel.   Breslau,  1846. 
239.  BERNARD.     Gaz.  Med.  de  Paris,  1850,  p.  889. 

232.  BRINTON.     London  Med.  Gaz  ,  18J9. 

"     BRINTON.     On  Food  and  its  Digestion.     Churchill,  1861,  p.  100. 
236.  BERNARD.     The  Med.  Times  and  Gaz.,  Aug.,  1860. 
11     LONGET.     Anat.  et  Phys  duSysteme  Nerveux,  &c.     Paris,  1842. 

Vol.  i,  p.  323. 

"     BISCHOFF      Muller:  Archiv.  far  Anat,  Phys.  und  wissenschaft- 
liche  Medecin.     Berlin,  1848.     Jahresbericht,  p.  140. 

239.  MEISSNER.     Henleund  Pfeufer:  Zeitschrift  fur  Rationelle  Medi- 

zin.     Heidelberg,  2d  Ser.,  vol.  viii. 

240.  LIEBERKUHN,  J.  N.     Diss.  de  Fabrica  et  Actione  Villorum  In- 

testinorum  tenuium.     1782, 

"     PEYER.     De  Glanduris  Intestinorum.     1682. 
"     BRUNN,  J.  C.     Glandulas  Duodeni  seu  Pancreas  secundarium. 

4to.     1715. 
251    MM.  BOUCHARDAT  ET  SANDRAS.     Gaz.  Mdd.  de  Paris,  Jan., 

1845. 
252.  DISCHARGE  OF  FATTY  MATTERS  FROM  INTESTINE.     Trans,  of 

the  Royal  Med.-Chir.  Soc.     Vol.  xviii,  p.  57. 

f     BERNARD.     Quarterly  Jour  of  Microscop.  Science.     Churchill. 
259.  TABULAR  COMPOSITION  OF  BILE,  by  Frerichs.    V.  Gorup-Besa- 

nez.     Physiologic  Chemie.     1862,  p.  469. 

26,1.  PRESENCE  OF  COPPER  IN  BILE  AND  BILIARY  CALCULI.  Gorup- 
Besanez.  Untersuchungen  iibcr  Galli.  Erlangen,  1846. 


LIST    OF    AUTHORS.  621 

VAGE 

261.  BLONDLOT.     Essai  sur  les  Fonctions  du  Foie.     Paris,  1846,  p.  62. 

"     KEMP.     Chemical  Gaz.     No.  99,  1846. 
263.  SIMON.     Animal  Chem.     Trans,  by  Dr,  Day  for  the  Sydenham 

Soc.     Vol.  ii.  p.  367. 
"     FRERICHS      Ranking:  Half-yearly  Abst.  of  the  Med.  Sciences. 

Churchill.     Vol.  iii,  314. 
268.   PAVY.     Phil.  Trans.     1800,  p.  595. 
"     PAVY.     On  the  Nature  and  Treatment  of  Diabetes.     Churchill. 

1862. 
274.   BRINTON      On  Food  and  its  Digestion,     Churchill.     1861. 

282.  KOLLIKER.    Annales  des  Sciences  Naturelles.    Geologie.     1846, 

p.  99. 

"  RECKLINGHAUSEN.  Art.  Lymphatic  System.  Strieker's  His- 
tology, translated  by  H.  Power.  Vol.  i. 

283.  KOLLIKER.     Brit,  and  For.  Med.-Chir    Rev.     July,  1850. 

286.  GULLIVER     Howson  :  Works,  Ed.  for  the  Syd.  Soc.  by  Mr.  Gul- 

liver, 1846-7,  p.  82,  note. 

287.  ASCHERSON.    Miiller:  Archiv.  fur  Anat.  Phys.  und  wissensehaft- 

liche  Medecin.     Berlin,  1840. 

288.  BOUISSON.     Gaz.  Med.  de  Paris.     1844. 

289.  OWEN  REES.     London  Med.  Gaz      Jan.,  1841. 

"  R.  VIRCHOW.  Die  Cellular  Pathologic  (since  translated  by  Dr. 
Chance).  Berlin,  1858,  s.  143. 

290.  BIDDER.  Miiller  :  Archiv.  fur  Anat.  Phys.  und  wissenschaftliche 

Medecin.     Berlin,  1845. 

"  SCHMIDT.  New  Syd.  Soc.'s  Year-Book  of  Med.,  &c.  London, 
1863,  p.  24. 

292.  HERBST.  Das  Lymphageiass  system  und  seine  Verrichtungen. 

Gottingen,  1844 

"  LYMPH-HEARTS.  J.  MULLER  Elements  of  Phys.,  trans,  by 
Dr.  Baly.  2d  ed.,  1840,  p.  293. 

293.  VOLKMANN.      Miiller:    Archiv.   fur  Anat.   Phys.  und  wissen- 

schaftliche Medecin.     Berlin,  1844. 
297.  BENCE  JONES.     Proceedings  of  the  Royal  Soc.     Vol.  xiv. 

"     SAVORY.     The  Lancet.     1863,  May  9  and  16. 
298     OESTERLEN.      Oesterreichische    Medecinische    Wochenschrift. 

Wien,  Feb.,  1844. 
"     OESTERLEN.     Archiv.  fiir  Phys.  und  Pathol.  Chemie  und  Mikro- 

scopie.     Von  J.  F.  Heller.     Wien,  1847,  p.  56. 

300.  HELMHOLTZ.     Miiller:    Archiv.  fiir  Anat.  Phys.  und  wissen- 
schaftliche Medecin.     Berlin,  1845. 
"     CARPENTER.     Princ.  of  Human  Phys.     3d  ed.,  p.  623. 

308.  BRODIE.     Lectures  on  Pathol.  and  Surg.     1846,  p.  309. 

u  TRAVERS.  Further  Inquiry  concerning  Constitutional  Irrita- 
tion, p.  436. 

"  BALY.  J.  Miiller :  Elements  of  Phys.  Transl.  by  Dr.  Baly.  2d 
ed.,  1840,  p.  396. 

309.  Defective  Nutrition  from  Irritation  of  Nerves  r  London  Med. 

,      Gaz.,  vol   xxxix,  p.  1022. 
315.  BOWMAN.     The  Cyclopaedia  of  Anat.  and  Phys.,  Edited  by  Dr. 

Todd.     Art.  Mucous  Membrane. 

324.  PERISTALTIC  MOVEMENTS  or  LARGE  GLAND-DUCTS.  J.  Muller  : 
Elements  of  Phys.     Translated  by  Dr.  Baly.     2d  ed.,  1840, 
p.  521. 
"     DR.  BROWN-SKQUARD.     Journ.  de  Phys.     1858. 


622  LIST    OF    AUTHORS. 


325.  CARPENTER.     Princ.  of  Human  Phys.    3d  ed.,  p.  476. 

"     SIMON.    A  Physiological  Essay  on  the  Thymus  Gland.    London, 
1845.    4to. 

326.  ECKER.     Der  feinere  Bau  der  Neben-nieren  beim  Menschen  und 

den  Vier  Wirbelthierclassen.     Braunschweig,  1846. 

330.  MEYER.     Boehm,  L.     De  Glandularum  intestinalium  Structura 

penitiori.     Berol.,  1835.     March,  1845. 
11     SIMON.    A  Physiological  Essay  on  the  Thymus  Gland.    London, 

1845.    4to" 

11     FRIEDLEBEN.     Die  Phys.  der  Thymusdriise.     Frankfurt.  1858. 
u     HUTCHINSON.      Funke :    Atlas   der    Phys.   Cheniie.      Leipzig, 

1853-6. 
"     WILKS.     Guy's  Hosp.  Kep.     1862. 

331.  KOLLIKER.    Manual  of  Human  Microscop.  Anat.    Parker,  1860, 

p.  374. 

"     KOLLIKER.     Manual,  &c.     p.  365. 

339.  KRAUSE.      K.    Wagner :    Handworterbueh   der   Phys.    Braun- 
schweig.   Article  Haut. 

"     ERASMUS  WILSON.      A  Practical   Treatise  on   Healthy  Skin. 
Churchill,  1846. 

344.  J.DAVY.   Trans,  of  the  Royal  Med.-Chir.Soc.  Vol.  xxvii,  p.  189. 
"     KRAUSE.     Bulletin  de  1' Academic  Royale  de  Medecine. 

345.  BERZELIUS.     Trait4  de  Chimie,  tradint  par  Esslinger.     8  vols. 

8vo.     Paris.     Vol.  vii  contains  the  Chemistry  of  Animal 

Structures. 
"     ANSELMINO.     Zoochemie,  by  D.  Lehmann.     Heidelberg,  1858, 

p.  301. 

"     GORUP-BESANEZ.     Lehrbuch  der  Phys.  Chemie.     1862,  p.  504. 
"     LAVOISIER  ET  SEQUIN.     Memoires  de  1'Acad  des  Sciences  de 

Paris.     1790. 

346.  KRAUSE.     Paget :  Reports  on  the  use  of  the  Microscope,  and  on 

the  Progress  of  Human  Anat.  and  Phys.  ;  in  the  Brit,  and 

For.  Med.  Rev.     1843-4,  p.  40. 
"     MILNE-EDWARDS.     Influence  des  Agens  Physiques  sur  la  Vie. 

Trans,  by  Dr.  Hodgkin. 
"     REQNAULT  ET  REISET.     Annales  de  Chimie  et  de  Pharmacie. 

1849. 
"     EDWARD  SMITH.     Dr.  Carpenter :  Princ.  of  Human  Phys.    5th 

ed.,  1855.    6th  ed.,  p.  293. 

347.  MILNE-EDWARDS  AND  MULLER.    J.  Mviller:  Elements  of  Phys. 

Trans,  by  Dr.  Baly.     2d  ed.,  1840,  p.  328. 
"     MAGENDIE.     Gaz.  Med.  de  Paris,  Dec.,  1843. 
"     MILNE-EDWARDS.     Influence  des  Agens  Physiques  sur  la  Vie. 

Translated  by  Dr.  Hodgkin. 

348.  MADDEN.     Experimental  Inquiry  into  the  Phys.  of  Cutaneous 

Absorption.     Edinburgh,  1835. 

"     BERTHOLD.     Miiller:    Archiv.  for  Anat.,   Phys.,  und  wissen- 
gchaftliche  Medecin.     Berlin,  1838,  p.  177. 

355.  ERICHSEN.     London  Med.  Gaz.     1845. 

356.  BERNARD.     Comptes  Reridus  des  Seances  de  1' Academic  Royale 

des  Sciences  de  Paris.     1846. 
358.  PROUT.     On  the  Nature,  &c. 

"     GOLDINQ  BIRD.     Urinary  Deposits.     1844.     p.  31. 

"     PARKES.     On  the  Composition  of  the  Urine.     1866. 
360.  WOHLER.     Annales  de  Chirnie  et  de  Pharmacie.     xxvii,  196. 


LIST    OF    AUTHORS.  623 

PAGE 

360.  LECANU.     Bulletin  de  1'Acad.  Royale  de  Med.     T.  xxv,  p.  261. 

361.  LEHMANN.     F.  Simon:   Animal  Chem.     Trans,  by  Dr.  Davy 

for  the  Syd.  Soc.     Vol.  ii,  p.  163. 
u     LASSIGNE.     Journal  de  Chimie  Medicale.     p.  272. 
"     MILLON.     Comptes  Rendus  des  Seances  de  1'Acad.  Royale  des 

Sciences  de  Paris.     1843. 

362.  G.  BIRD.     London  Med.  Gaz.     Vol.  xli,  p.  1106. 
"     LIEBIG.     The  Lancet,  June,  1844. 

363.  LIEBIG.     The  Lancet,  June,  1844. 

"     WEISMANN.     Henle   und   Pfeufer:    Zeitschrift   fur   Rationelle 

Medizin.     Heidelberg.     3  ser.,  p.  837. 
"     URE.  Transac.  of  the  Royal  Med. -Chir.  Soc.     Vol.  xxiv. 

364.  LIKBIG.  Chem.  of  Food.     Walton  and  Maberly,  1847. 

"     HEINTZ.     Canstatt:  Jahresbericht  uber  die  Fortschritte  in  der 
Biologie.     Erlangen,  1847,  p.  105. 

365.  RONALDS.     Philosophical  Mag.     1846. 

370.  LISTER  AND  TURNER.    Quar.  Jour,  of  Microscop.  Science.    1850. 
"     LOCKHART  CLARKE.     Philosoph.  Transac.     1859. 
"     STILLING.     Ueber  den  Bau  der  Nerve n-primitivfaser  und  der 

Nerven-zelle.     1856. 
873.  GULL.     The  Med.  Times.     1849. 
"     KOLLIKER.      Manual  of  Human  Microscopic  Anat.      Parker, 

1860,  p.  248. 

PACINI.    AnnaliUniversalidi  Medicini.    Luglio.     1845,  p.  208. 
379.  HELMHOLTZ  AND  BAXT.     Camb.  Journ.  of  Anat.  and  Phys. 

P.  i,  new  series,  p.  190. 
"     RUTHERFORD.     Lancet,  April  1st,  1871. 
382.  SAVORY.     Lancet,  August  1st,  1868. 

389.  LOCKHART  CLARKE.     Philosoph.  Transac.     1851  to  1859. 
391.   KOLLIKER.     Manual   of  Human   Microscopic   Anat.     Parker. 

1860.     p.  244. 
393.  BROWN-SEQUARD.     On  the  Phys.  and  Pathol.  of  the  Cerebral 

Nervous  System.     Philadelphia,  1860. 
401.  VOLKMANN.     Miiller:  Archiv.  fur  Anat.,  Phys.,  und  wissen- 

schaftliche  Medecin.     Berlin,  1844. 
408.  J.  REID.     Edinburgh  Med.  and  Surg.  Journ.     1838. 

415.  LONGET.      Anat.  et  Phys.  du  Systeme  Nerveux,  &c.      Paris, 

1842.     T.  i,  p.  733,  and  others. 

"     FLOURENS.     Recherches  Experimentales  sur  les  Fonc.  du  Sys- 
teme Nerveux,  &c.     Paris. 

"     MAGENDIE.     Le9ons  sur  les  Functions  du  Systeme  Nerveux. 

416.  BOUILLAUD.     Recherches  Cliniques  et   Experimentales  sur   le 

Cervelet.     Referred  to  by. 

"     LONGET.     Anat.   et  Phys.   du  Systeme  Nerveux,   &c.     Paris, 
1842.     T.  i,  p.  740. 

417.  LONGET.     Anat.   et   Phys.    du  Systeme  Nerveux,   &c.     Paris, 

1842.     T.  i,  p.  762. 
"     COMBIETTE.     Revue  Medicale. 
426.  GRANT.     See  Longet,  1.  c.     T.  ii,  p.  388. 
430.  VALENTIN.    Lehrbuch  der  Phys.  des  Menschen.    Braunschweig, 

1844.     Vol.  ii,  p.  666. 

436.  RKID.     Edinburgh  Med.  and  Surg.  Journ.     1838. 
439.  BIDDER  UND  VOLKMANN.     R.  Wagner:  Handworterbuch  der 

Phys.      Braunschweig.     Art.  Nervenphysiologie 
"     REID.     Edinburgh  Med.  and  Surg.  Journ.     Vols.  xlix  and  Ii. 


624  LIST    OF     AUTHORS. 

PAGE 

441.  REID.     Edinburgh  Med.  and  Surg.  Journ.     Vols.  xlix  and  li. 
11     LEGALLIOS.     (Euvres  Completes,  Edited  by  M.  Poriset.     Paris, 

1830 
u     TRAUBE.     Beitrage  zur  Experimentellen  Pathologie  und  Phys. 

Berlin,  1840. 

443.  BERNARD.     Archives  Generales  de  Me"decine.     1844. 
454.  KUHNE.     Canib.  Journ.  of  Anat.  and  Phys.     Part  ii. 
456.  KOLLIKER.     Manual  of  Human  Microscopic  Anat.       Parker, 

1860.     p.  63. 
459.  SHARPEY.     Quain  :  Anat.     7th  ed. 

461.  SEGALAS.     J.  Muller:  Elements  of  Phys.     Trans,  by  Dr.  Baly. 

2d  ed  ,  1840,  p.  895. 

462.  BOWMAN.     Phil.  Trans.     1840,  1841. 

"  No  DIMINUTION  IN  BULK  or  CONTRACTING  MUSCLE.  Mayo, 
J.  Muller:  Elements  of  Phys.;  Trans,  by  Dr.  Baly. 
2d  ed.,  1840,  p.  886.  Valentin:  Lehrbuch  der  Phys.  des 
Menschen.  Braunschweig,  1844.  Matteucci :  Erdmann's 
Jour. 

463.  ED.  WEBER.    R.  Wagner :  Handworterbuch  der  Phys.    Braun- 

schweig.    Art.  Muskelbewegung. 

464.  ED.  WEBER.    K.  Wagner :  Handworterbuch  der  Phys.    Braun- 

schweig.    Art.  Muskelbewegung. 

465.  SCHIFFER:  Camb.  Journ.     Part  ii,  new  series,  p.  416  ;  Part  iii, 

new  series,  p.  236. 

466.  BROWN-SEQUARD.     Proc.  of  the  Royal  Soc.     1862,  p.  204. 
"     BROWN-S£QUARD.     London  Med.  Gaz.     May  16,  1851. 

"  VALENTIN.  Lehrbuch  der  Phys.  des  Menschen.  Braunschweig, 
1844.  Bd.  ii,  p.  36. 

485.  PETREQUIN  ET  DIDAY.     Gaz.  M6d.  de  Paris. 

488.  MULLER  UND  COLOMBAT.  Froriep :  Neue  Notizen  aus  dem 
Gebiete  der  Natur.  Weimar,  1840. 

491.  MAGENDIE.     Journ.  de  Phys.     T.  iv,  p.  180. 

513.  VOLKMANN.  R.  Wagner :  flandworterbuch  der  Phys.  Braun- 
schweig. Art.  Sehen,  p.  286. 

538.  Note.  ED.  WEBER.  Archives  d'Anat.  Generale  et  de  Phys. 
1846. 

555.  SCHIFF  AND  BROWN-S^QUARD.     The  Lancet,  1858. 

"  SIEVEKIVG.  Brit,  and  For.  Med.-Chir.  Rev.,  1858.  Vol.  ii, 
p.  501. 

556.  VALENTIN.    Lohrbuch  der  Phys.  des  Menschen.    Braunschweig, 

1844.     Vol.  ii,  p.  566.  * 
566.  VALENTIN.     Muller:    Archiv.   fur  Anat.   Phys.,  und  wissen- 

schaftliche  Medecin.     Berlin,  1838. 
572,  DALTON.     Phys.     1864,  p.  585. 
579.  BISCHOFF.     Entwickelungs-Geschichte  der  Saugethierc  und  des 

Menschen.     1842. 

589.  H.  MULLER.    Brit,  and  For.  Med.-Chir.  Rev.    Vol.  xiii,  p.  546. 
592.  HARVEY.     On  a  remarkable  Effect  of  Cross-Breeding.     By  Dr. 

Alex.  Harvey.     Blackwood  &  Sons,  1851. 
"     HUTCHINSON.     Med.  Times  and  Gaz  ,  Dec.,  1856. 
"     SAVORY.     On  Effects  upon  the  Mother  of  Poisoning  the  Foetus. 

Pamphlet,  1858. 
599.  KOLLIKER.    Annales  des  Sciences  Naturelles :  Zoologie.    Aug., 

1846. 


INDEX. 


Abdominal  muscles,  action  of  in  res- 
piration, 165 

type  of  respiration,  163 
Aberration,  chromatic,  510 

spherical,  509 

Absorbents.     See  Lymphatics. 
Absorption,  277 

by  bloodvessels,  293 

of  gases  by  blood,  296 

by  lacteal  vessels,  248,  290 

by  lymphatics,  291 

of  oxygen  by  lungs,  177 

process  of  by  osmosis,  294 

purposes  of,  277 

rapidity  of,  297 

from  rectum,  rapidity  of,  297 

by  the  skin,  347 

from  stomach,  preparation  of  food 
for,  229 

See   Chyle,  Lymph,  Lymphatics, 

Lacteals. 
Accessory  nerve,  443 

distribution  of,  443 

roots  of,  444 
Accidental   elements  in  human  body, 

26 
Accidents,  involuntary  movements  in, 

400 

Acetic  acid  in  gastric  fluid,  222 
Acids,  strong,  prevent  coagulation,  64 
Acini  of  secreting  glands,  319 
Adaptation  of  the   eye   to   distances, 

510 

Adenoid  tissue.    See  Retiform  Tissue. 
Adipose  tissue,  40 

situations  of,  40 

structure  of,  41 

See  Fat. 
Afferent  arteries  of  kidney,  352 

lymphatics,  286 

nerve-fibres,  376 
After-birth,  593 
After-sensations  of  taste,  553 

of  touch,  558 

of  vision,  517 


Age,  in  relation  to  blood,  76 
to  capacity  of  chest,  168 
to  excretion  of  urea,  360 
to  exhalation  of  carbonic  acid,  173 
to  heat  of  body,  189 
to  mental  faculties,  422 
to  pulse,  109 
to  respiration,    168 
to  voice,  484 
Aggregated  glands,  319 
Agminate  glands,  241 
Air,  atmospheric,  composition  of,  173 
changes  by  breathing,   173 
favors  coagulation  of  blood,  63 
quantity  breathed,  166 
states  of  influencing    production 

of  carbonic  acid,  175,  176 
transmissions  of  sonorous   vibra- 
tions through,  536 
in  tympanum,  necessary  for  hear- 
ing, 538 

undulations  of,  conducted  by  ex- 
ternal ear,  534 
by  tympanum,  537 
Air-cells.  158 
Air-tubes.     See  Bronchi. 
Albinos,  imperfect  vision  in,  501 
Albumen,  action  of  gastric  fluid  on, 

229 

characters  of,  22 
chemical  composition  of,  23 
coagulated,  properties  of,  22 
coating  oily  matter,  287 
relation  to  fibrin,  22 
tissues  and  secretion  in  which  it 

exists,  22 
of  blood,  74 

uses  of,  86 
vegetable,  202 
Albuminose,  229 

action  of  liver  on,  266 
Albuminous  substances,  21 
absorption  of,  271 
action  of  gastric  fluid  on,  229,  271 
of  liver  on,  229 
of  pancreas  on,  252,  271 


626 


INDEX. 


Alcoholic  drinks,  effect  on  respiratory 

changes,   176 
Aliments.     See  Food. 
Alimentary  canal,    development     of, 
606.       See  Stomach,    Intestines, 
Ac. 
Alkalies,  caustic,  prevent  coagulation, 

64 
Alkaline  and  earthy  salts,  influence  of 

on  coagulation,  63 
Allantois,  585,  586 
Aluminium,  an  accidental  element  in 

tissues,  26 
Amoeba,  72 

Amoeboid  movements  of  white  corpus- 
cles, 72 
Amaurosis,  action  of  iris  in,  425 

after  injury  of  the  fifth  nerve,  432 
Ammonia  in  blood,  76 

cyanate   of,  identical  with   urea, 

360 
exhaled  from  lungs,  179 

from  skin,  345 
urate  of,  363 
Amnion,  585 
Ampulla,  531 

Amputations,  sensations  after,  381 
Amylaceous  principles,  action  of  gas- 
tric fluid  on,  230 
of  pancreas  and  intestinal  glands 

on,  250,251,  271 
of  saliva  on,  213 
Amyloid  substance  in  liver,  267 
Amyloids,  200 
Anastomoses   of    muscular   fibres   of 

heart,  460 
of  nerves,  372 
of  veins,  144 
in  erectile  tissues,  153 
Anatomical  elements  of  human  body, 

26-33 

Angle,  optical,  514 
Angulus  opticus  seu  visorius,  514 
Ani  sphincter.     See  Sphincter. 
Animal  fats,  20 

food,  digestion  of,  228 

in  relation  to  urea,  361 

in  relation  to  uric  acid,  362 

in    relation    to    reaction    of 

urine,  356 

heat,  189.     See  Heat  and   Tem- 
perature, 
life,  muscles  of,  458 

nervous  system  of,  368 
starch.  267 
Animals,  their  distinction  from  plants, 

15 
Anterior  pyramids,  403 

roots  of  spinal  nerves.  391 
Antihelix,  527 
Antitragus,  527 


Anus,  249 
Aorta,  91 

development  of,  599 
elasticity  of,  117 
pressure  of  blood  in.  131 
valves  of,  96 

action  of,  101 
Apnoea,  force  of  inspiratory  efforts  in, 

170.     See  Asphyxia. 
Apoplexy,  effects  of,  420 

with  cross  paralysis,  405 
Appendices  epiploicae,  249 
Appendix  vermiformis,  249 
Aqugeductus  cochleae,  532 

vestibuli,  530 
Aqueous  humor,  505 
Arches,  visceral,  596 
Area  germinativa,  581 
pellucida,  580 
vasculosa,  587 
Areola  of  nipple,  614 
Areolar  tissue,  38 
functions  of,  40 
situations  where  found,  39 
Arteries,  88,  115 

calibre  of,  how  regulated,  118, 121 

coats  of,  115 

muscular  contraction  of,  118 

effect  of  cold  on,  119 

effect  of  division,  119 

of  electro-magnetism,  120 
elasticity  of,  116,  117 

purposes  of,  1 16 
elongation  and  dilatation  in  the 

pulse,  123 

force  of  blood  in,  130,  131 
muscularity  of,  115 

evidence  of,  118 
governed  by  nervous  system,  121, 

122,  451 
purpose  of,  121 
nerves  of,  121 
office  of,  116 

pulse  in,  123.     See  Pulse, 
structure  of,  115 
distinction   in    large   and    small 

arteries,  115 
systemic,  91 

velocity  of  blood  in,  131 
Articular  cartilage,  43 
Articulate   sounds,    classification  of, 

487.     See  Vowels  and  Consonants 
Artificial  digestive  fluid,  224 
Arytenoid  cartilages,  478 

effect  of  approximation,  481 
movements  of,  478 
muscle,  478,  479 
Asphyxia,  186 

cause  of  death  in,  186 
experiments  on,  186 
essential  cause  of,  188 


INDEX. 


627 


Assimilation  or  maintenance  of  blood, 
84 

nutritive,  299 
Atmospheric  air.      See.  Air. 

pressure  in  relation  to  respiration, 

161 
Atrophy,  from  deficient  blood,  307 

from  disensed  nerves,  309 
Attention,  influence  of,  on  sensations, 
493 

on  special  senses,  516 
Auditory  canal,  527 

function  of,  534 
Auditory  nerve,  533 

distribution  of,  533,  541 

effects  of  irritation  of,  546 

fibres  of.  377 

sensibility  of,  543 
Auricle  of  ear,  527 
Auricles  of  heart,  91 

action  of,  96 

capacity  of,  111 

development  of,  599 

dilatation  of,  99 

force  of  contraction  of,  110 
Axis-cylinder  of  nerve-fibre,  370 
Azote.     See  Nitrogen. 
Azotized  principles,  21 


Baritone  voice,  483,  484 

Basement-membrane,  of  mucous  mem- 
branes, 318 
of  secreting  membranes,  314 

Bass  voice,  483 

Benzoic    acid,    relation    to   hippuric 
acid,  363 

Bicuspid  valve,  92 

Bile,  259 

antiseptic  power  of,  265 
coloring  matter  of,  260 
coloring  serous  secretions,  316 
composition  of.  259 

elementary,  261 
digestive  properties  of,  265 
excrementitious,  262 
fat  made    capable  of  absorption 

by,  265 

functions  of  in  digestion,  265 
mixture  with  chyme,  270 
mucus  in,  260 
a  natural  purgative,  265 
process  of  secretion  of,  262 
purposes  of,  262 

in   relation  to  animal   heat, 

264 

quantity  secreted,  262 
reabsorption  of,  263,  265 
saline  constituents  of,  260 
secretion  and  flow  of,  262 
secretion  of  in  foetus,  263 


Bile,  tests  for.  261 
Bilin,  259    , 

reabsorption  of,  263 
Biliverdin  and  bilifulvin,  260 
Bipolar  nerve-corpuscles,  375 
Birds,  their   high  temperature,   191, 

192 

Birth,  13 

Bladder,  urinary.      See  Urinary  Blad- 
der. 

Blastema,  27 

Blastoderuiic  membrane,  581 
Bleeding,  effects  of  on  blood,  76 
Blood,  55-87 

adaptation  of  to  tissues,  306 
adequate    supply    necessary    for 

nutrition,  307 
albumen  of,  74 
use  of,  86 

alteration  of  by  disease,  84 
ammonia  in.  76 
animal  poisons,  how    affected  by, 

306 
arterial   and   venous,    differences 

between,  77,  81,  180 
assimilation  of,  84 
casein  in,  75 

changes  in  by  respiration,  179 
chemical  composition  of,  64 
circulation  of,   88.     See  Circula- 
tion, 
coagulation  of,  58-62 

circumstances  influencing,  62 
color  of,  56 

changed  by  respiration,  179 
differences  in,  77 
coloring  matters  in,  76 
coloring  matter,  relation  to  that 

of  bile,  260 
compared    with    lymph    and 

chyle,  286 
composition  of,  chemical,  64 

physical,  56 
'  variations  in,  76-80 
conditions  necessary  to  nutrition, 

306 
corpuscles  or  cells  of,  65-72.     See 

Blood-corpuscles, 
red,  67 
white,  71 

creatin  and  creatinin  in,  75 
crystals  of,  69 
development  of,  81 

from  lymph  or  chyle,  83 
exposure  to  air  in  lungs,  159 
extractive  matters  of,  75 
fatty  matters  in,  74 

use  of.  86 
fibrin  of,  74 

separation  of,  22,  23,  62 
use  of,  86 


628 


INDEX. 


Blood,  force  of  in  arteries,  131 
formation  of  in  liver,  83 

in  spleen,  327 
gases  in,  81 

changed  by  respiration,  180 
of  gastric  and  mesenteric  veins,  79 
globulin  of,  68,  69 
glucose  or  grape-sugar  in,  75 
growth  and  maintenance  of,  85 
haematin  or  cruorin  of.  71 
hepatic,  characters  of,  80 
hippuric  acid  in,  76 
inorganic  constituents  of,  75 
lactic  acid  in,  76 
menstrual,  56,  569 
molecules  or  granules  in,  72 
movement  of,  in  capillaries,  137 

in  lungs,  172 
odoriferous  matters  in,  76 
odor  or  halitus  of,  56 
portal,  characters  of,  80 

purification  of  by  liver,  264 
quantity  of,  56 
reabsorption  of  bile  into,  263 
reaction  of,  56 
relation  of  to  lymph,  289 

to  secretions,  319,  321,  323 
of  rennl  vein,  80 
saline  constituents  of,  75 

uses  of,  86 
serum  of,  72 

compared    with   secretion  of 

serous  membrane,  316 
specific  gravity  of,  56 
splenic,  characters  of,  80 
structural  composition  of,  56 
supply  of,  adapted  to  each  part, 

122 

to  brain.  151 

necessary  for  nutrition,  307 
necessary  to  secretion,  323 
temperature  of,  56 
urea  in,  76 
uric  acid  in,  76 
uses  of,  85 

variations  of  in  different  circum- 
stances, 76 

in  different  parts  of  body,  77 
water  in,  73 
Blood-corpuscles,'   red,  characters    of, 

65 

chemical  composition  of,  68 
development  of,  81-83,  304 
in  liver,  83 
in  spleen,  327,  328 
disintegration  and  removal  of,  329 
diversities  of,  67 
movement  of  in  capillaries,  138 
sinking  of,  59 
tendency  to  adhere,  60,  68 
uses  of,  87 


Blood-corpuscles,  white,  71 

amoeboid  movements  of,  72 
formation  of  in  spleen,  328 
Blood-crystals,  69 

Bloodvessels  absorption  by,  29,3-298 
circumstances    influencing,    297, 

298 

difference  from  lymphatic  absorp- 
tion, 293,  294 

osmotic  character  of,  294,  296 
rapidity  of,  297 
area  of,   137 
communication  with  lymphatics, 

282 

development  of,  598 
influence   of  nervous   system  on, 

452 

of  placenta,  589 
relation  to  secretion,  324 
share  in  nutrition,  306 
Bone,  46 

canaliouli  of,  48 
cancellous  structure  of,  46 
composition  of,  46 
development  of,  49 
Haversian  canals  of,  48 
lacunae  of,  48 
lamellae  of,  48 
periosteum  of,  47 
structure  of,  46 
Bone-earth,  composition  of,  26 
Bones  or  ossicles  of  ear,  529 
Bones,  growth  of,  299 

nutrition  of,  305 
Boys,  voice  of,  484 
Brain.       See   Cerebellum,    Cerebrum, 

Pons,  &c. 
capillaries  of,  134 
circulation  of  blood  in,  150 
development  of,  582,  605 
disease  of,  with  atrophy,  307 
influence  on  heart's  action.  Ill 
quantity  of  blood  in.  152 
Breathing-air,  166 
Breathing.     See  Respiration. 
Bronchi,   arrangement  and   structure 

of,  157 

muscularity  of,  171 
Bronchial  arteries  and  veins,  172,  173 
Brunn's  glands,  245 
Buccinator  muscle,  nervous  supply  of, 

428 

Buflfy  coat,  formation  of,  59,  68 
Bulbus  arteriosus,  599 
Bursae  mucosse,  315 


Caecum,  250 

changes  of  food  in,  273 
Calcium,  salts  of  in  human  body,  25 


INDEX. 


629 


Calculi,     biliary,    containing   choles- 

terin,  20 

containing  copper,  261 
Calculus,  radiation  of  sensation  from, 

385,  395 

Calorifaeient  food,  202 
Calyces  of  the  kidney,  350 
Calyciform  papillae  of  tongue,  548 
Canal,  alimentary.     See  Stomach,  In- 
testine, &G. 
external  auditory,  527 
function  of,  534 
oral,  488 

of  spinal  cord,  390 
spiral,  of  cochlea,  531 
Canaliculi  of  bone.  48 
Canals,  Haversian,  48 
portal,  254 
semicircular,  530 
function  of,  541 
Cancellous  texture  of  bone,  46 
Capacity  of  chest,  vital,  167 

how  increased  or  diminished,  162- 

165 

of  heart,  109 
Capillaries,  88,  131 

circulation  in,  135 

rate  of,  137 
contraction  of,  138 
development  of,  599 
diameter  of,  132 
influence  of  on  circulation,  139 
lymphatic,  280 
network  of,  133 
number  of,  134 
passage    of     corpuscles    through 

walls  of,  138 

resistance  to  flow  of  blood  in,  136 
still  layer  in,  137 
structure  of,  132 
systemic,  91 
of  lungs,  159,  160,  172 
of  muscle,  460 
of  stomach,  219 
Capsule  of  Qlisson,  254 
Capsules,  Malpighian,  351 
Carbon,    union   of  with   oxygen,  pro- 
ducing heat,  192,  193 
Carbonic  acid  in  atmosphere,  173 
in  blood,  79,  80,  180 
effect  of  in  producing  asphyxia, 

188,  189 

exhaled  from  skin,  345 
increase  of  in  breathed  air,  173 
in  lungs,  171 
in  relation  to  heat  of  body,  192, 

193 

Cardiac  orifice,  action  of,  231 
sphincter  of,  183 

relaxation  in  vomiting,  233 


Cardiac    branches    of    pneumogastric 

nerve,  439 
Cardiograph,  108 
Jarnivorous  animals,  food  of,  202 

sense  of  smell  in,  498 
!artilage,  43 
articular,  44 
cellular,  44 

chondrin  obtained  from,  21 
elastic,  43 

fibrous,  45.     See  Fibro-cartilage. 
hyaline,  44 
matrix  of,  44 
ossification  in,  50 
perichondrium  of,  43 
permanent,  43 
structure  of,  43 
temporary,  43,  44 
uses  of,  46 
varieties  of,  43 

Cartilage  of  external  ear,  use  in  hear- 
ing, 535 

Cartilages  of  larynx.  477,  478 
of  ribs,  elasticity  of,  164 
Casein  in  blood,  76 
Catalytic  process,  225 
Cauda  equina,  388 
Caudate  ganglion-corpuscles,  375 
Cells,  primary  or  elementary,    defini- 
tion of,  31 
contents  of,  32 
shape  of,  31 
structure  of,  31 

blood,  65.     See  Blood-corpuscles, 
cartilage,  43 
embryonic,  81 

epithelium,  34,  38.     See  Epithe- 
lium, 
of  glands,  35,  322 

action  of  in  secretion,  323 
lacunar  of  bone,  48 
mastoid,  528 
nerves  ending  in,  373 
olfactory,  495 
pigment,  42 
of  stomach,  216 
Cellular  cartilage,  44 
Cellular    tissue,     38.        See    Areolar 

Tissue. 

Cement  of  teeth,  51,  53 
Centres,  nervous.     See  Nervous  Cen- 
tres. 

of  ossification,  50 
Centrifugal  nerve-fibres,  377 
Centripetal  nerve-fibres,  376 
Cerebellum,  414 

co-ordinate  function  of,  415 

cross-action  of,  418 

effects  of  injury  of  crura,  418 

of  removal  of,  416 
functions  of,  415 


53 


630 


INDEX. 


Cerebellum,  in   relation  to  sensation, 

415 

to  motion,  415 
to  muscular  sense,  416 
to  sexual  passion,  417 
structure  of,  414 
Cerebral  circulation,  150 

ganglia,  function  of.  412,  413 
hemispheres.     See  Cerebrum. 
Cerebral  nerves,  424 

arrangement  of,  424 
third,  425 

effects  of  irritation  and  injury 

of,  425 

relation  of  to  iris,  425 
fourth,  426 
fifth,  428 

a  conductor  of  reflex  impres- 
sions, 430 

distribution  of,  428,  429 
effect  of  division  of,  309,  431 
influence  of  on  iris,  430 

on   muscles  of  mastica- 
tion, 428 
on  muscular  movements, 

430 
on  organs  of  special  sense, 

431,  433 

relation  of  to  nutrition,  431 
resemblance  to  spinal  nerves,  428 
sensitive  function  of  greater 

division  of,  429 
sixth,  426 

communication  of,  with  sym- 
pathetic, 427 
seventh.    See  Auditory  Nerve  and 

Facial  Nerve. 

eighth.      See  Glosso-pharyngeal, 
Pneumogastric,    and    Spinal 
Accessory  Nerves, 
ninth,  444 
Cerebro-spinal   nervous  system,    637, 

386 
influence    on   organic    life,    453. 

See  Brain,  Spinal  Cord,  Ac. 
Cerebro-spinal   fluid,  relation  to  cir- 
culation, 152 

Cerebrum,  its  structure,  419 
convolutions  of,  420 
crura  of,  409 
development  of,  603 
effects  of  injury  of,  420 
functions  of,  420 
in  relation  to  speech,  422 
relation  to  mental  faculties,  421 
Cerumen,  or  ear-wax,  339.  527 
Chalkstones,  362 
Chambers  of  eye,  505 
Charcoal,  absorption  of,  298 
Chemical  actions,  how  perceived,  493 


Chemical  composition   of  the  human 
body,  18 

distinctions  between  animals  and 
vegetables,  15 

sources  of  heat  in  the  body,  192, 
193 

stimuli,  action  of  nerves   excited 

by,  378 
Chest,  its  capacity,  167 

contents  of,  88,  162 

contraction  of  in  expiration,  163 

enlargement  of  in  inspiration,  162 
Chest-notes,  485 
Children,  respiration  in,  163 
Chlorine,  action  on  negro's  skin,  348 

in  human  body,  25 

in  urine,  366 

Chloroform,  effects  of,  408 
Cholesterin,  properties  of,  20 

in  bile,  260 

in  blood,  74 

Chondrin,  properties  of,  21 
Chorda  dorsalis,  582 
Chorda  tyrapani,  433 
Chordae  tendineae,  94 

action  of.  101 
Chorion,  588 

villi  of,  588 
Choroid  coat  of  eye,  500.  501 

use  of  pigment  of,  501 
Chromatic  aberration,  510 
Chyle,  279,  286 

absorption  of,  290 

analysis  of,  289 

bile  essential  to,  265 

coagulation  of,  287 

compared  with  lymph,  289 

corpuscles    of,    288.     See   Chyle- 
corpuscles. 

course  of,  278 

fibrin  of,  287 

forces  propelling,  282 

molecular  base  of,  287 

properties  of,  286 

quantity  found,  290 

relation  of  to  blood,  289,  290 
Chyle-corpuscles,  288 

development    into    blood-corpus- 
cles. 83,  288 
Chyme,  225.  270 

absorption  of  digested  parts  of, 
270 

changes  of  in  intestines,  270 
Cicatrix,  effect  of  nutrition  on,  310 
Cilia,  36,  37.  454 
Ciliary  epithelium,  36 

of  air-passages,  157 

function  of,  38 
Ciliary  motion,  37,  454 

action  of  in  bronchial  tubes,  172 


INDEX. 


631 


Ciliary    motion,   independent   of  ner- 
vous system,  454 
nature  of,  455 
Ciliary  muscle,  507 

action    of  in  adaptation   to    dis- 
tances, 511 
Ciliary  processes,  501 
Circulation  of  blood,  83 

action  of  heart  on,  96-104 
agents  concerned  in,  145 
in  arteries,  115 
force  of,  129 
velocity  of,  131 
in  brain.  150 
in  capillaries,  135 

rate  of,  137 
course  of,  89,  91 
in  erectile  structures,  152 
in  foetus,  601 

forces  acting  in,  90,  91,  145 
influence  of  respiration  on,  145 
peculiarities  of  in  different  parts, 

150 

portal,  90 

pulmonary,  89,  172 
systemic,  89.,  92 
in  veins,  141 

affected    by    muscular    pres- 
sure, 143 
by    respiratory    movements, 

146 

velocity  of,  147 
velocity  of,  147 
Circulus  venosus,  588 
Circumferential  fibro-cartilages,  45 
Circumvallate  papillee,  548 
Cleaving  of  yelk,  process  of,  579 
Cleft,  ocular,  604 
Clefts,  visceral,  596 
Climate,  relation  of  to  heat  of  body, 

191 
Clitoris,  562 

development  of,  612 
an  erectile  structure,  153 
Clot  or  coagulum  of  blood,  58 

contraction  of,  59.     See  Coagula- 
tion. 

of  chyle,  287 

Coagulation  of  albumen,  22 
of  blood,  58 

conditions  affecting,  62 
influence  of   respiration  on, 

179,  180 
theories  of,  61 
of  chyle,  288 
of  lymph,  289 
Cochlea  of  the  ear,  530,  531 

office  of,  542 
Cold-blooded  animals,  192 

extent  of  reflex  movements  in,  397 


Cold-blooded    animals,    retention     of 

muscular  irritability  in,  464 
Collateral  circulation  in  veins,  143 
Colloids,  295 
Colon,  248 
Colostrum,  615 
Coloring  matters,  24 
Coloring  matter  of  bile,  260 

of  blood,  68,  69 

of  urine.  364 

Colors,  optical  phenomena  of,  517 
Columnao  carnese,  94 

action  of,  98 
Columnar  epithelium,  35 

layer  of  retina,  502 
Columns  of  medulla  oblongata,  402 
Columns  of  spinal  cord,  388 

functions  of,  393 

Combined   movements,  office  of  cere- 
bellum in,  416 

Commissure  of  spinal  cord,  388 
Complemental  air,  166 

colors,  518 
Concha,  527 

use  of,  534 

Conduction  of  impressions,  in  medulla 
oblongata,  405 

in  or  through  nerve-centres,  383 

in  nerve-fibres,  376 

in  spinal  cord,  392 

in  sympathetic  nerve,  449 
Conductors,  nerve-fibres  as,  376 
Conglomerate  glands,  319 
Coni  vasculosi,  573 
Conical  papillae.  550 
Conjunctiva,  500 

Connective    tissue,   38.     See   Areolar 
Tissue. 

corpuscles,  40 
Consonants,  487 

varieties  of,  488 
Contractility,  of  arteries,  118 

of  bronchial  tubes,  171 

of  muscular  tissue,  461 

of  influence  of  nerves  on,  461 
Contraction,  of  coagulated  fibrin,  59 

of  muscular  tissue,  mode  of.  462 
Contralto  voice,  483 
Convoluted  glands,  321 
Convolutions,  cerebral,  420 
Co-ordination  of  movements,  office  of 

cerebellum  in,  416 
office  of  sympathetic  ganglia  in, 

451 

Copper,  an  accidental  element  in  the 
body,  26 

in  bile,  261 
Cord,  spinal.     See  Spinal  Cord. 

umbilical,  593 
Cords,  tendinous,  in  heart,  94 

vocal.     See  Vocal  Cords. 


632 


INDEX. 


Corium,  323,  324 
Cornea,  500 

action  of  on  rays  of  light,  505 
nutrition  of,  309 
protective  function  of,  507 
ulceration  of,  in  imperfect  nutri- 
tion, 309 

after  injury  of  fifth  nerve,  309,  431 
Corpora  Arantii,  96,  104,  105 
geniculata,  409 
quadrigeinina,  409 

their  function,  411 
stria ta,  409 

their  function,  411 
Corpus  callosum,  office  of,  422 
cavernosum  penis,  153 
dentatum,  415 
luteum,  570 

of  human  female,  570 
of  mammalian  animals,  571 
of    menstruation    and    preg- 
nancy compared,  572 
spongiosuui  urethrae,  153 
Corpuscles  of  blood.     See  Blood-cor- 
puscles, 
of  chyle,  288 
of  connective  tissue,  40 
of  lymph,  286 

nerve.     See  Nerve-corpuscles. 
Pacinian,  373 
Cortical  substance  of  kidney,  350 

of  lymphatic  glands,  283 
Corti's  rods,  532 
office  of,  543 

Costal  types  of  respiration,  163 
Coughing,  influence  on  circulation  in 

veins,  146 
mechanism  of,  182 
sensation  in  larynx  before,  384 
Cowper's  glands,  573 

office  uncertain,  577 
Cracked  voice,  484 
Cramp,  383,  392 
Cranium,  development  of,  595 
Crassamentum,  58 
Creatin  and  Creatinin,  24 
in  blood,  75 
in  urine,  364 

Crico-arytenoid  muscles,  479,  480 
Cricoid  cartilages,  478 
Cross  paralysis,  405 
Crura  cerebelli,  414 

effect  of  dividing,  418 
of  irritating,  415 
cerebri,  409 

effects  of  dividing,  411 
their  office,  411 
Crusta  petrosa,  51,  53 
Cryptogamio    plants,    movements    of 

spores  of,  16 
Crystalline  lens,  506 


Crystalline  lens,  in  relation  to  vision 
at  different  distances,  511 

masses  in  ear,  541 
Crystalloids,  295 
Crystals,  growth  of,  14 

in  blood,  69 

Cupped  appearance  of  blood-clot,  59 
Curves  of  arteries,  123 
Cuticle.     See  Epidermis,  Epithelium. 

of  hair,  340 

thickening  of,  311 
Cutis  anserina,  457 

vera,  333,  334 
Cyanate  of  ammonia,  360 
Cylindrical  epithelium,  36 
Cystic  duct,  252,  262 
Cystin  in  urine,  367 
Cytoblasts,  29 

in  developing  and  growing  parts, 
305 


Day,  time  of,  influence  on  exhalation 

of  carbonic  acid,  176 
Decapitated   animals,  reflex    acts  in, 

396,  397 

Decay  of  blood-corpuscles,  83 
Decidua,  591 

reflexa,  591 

serotina,  591 

vera,  591 
Decomposition,    tendency   of   animal 

compounds  to,  20 

Decussation  of  fibres  in   medulla  ob- 
longata,  404,  405 

in  spinal  cord,  394 

of  optic  nerves,  524 
Defecation,  mechanism  of,  183 

influence  of  spinal  cord  on,  401 
Degeneration  of  tooth-fangs,  303 
Deglutition,  213 

connection  with   medulla  oblon- 
gata,  408 

a  reflex  act,  396 

relation   of  pneumogastric   nerve 

to,  439 

Dental  groove,  primitive,  53 
Dentine,  51 
Depressor  nerve,  442 
Derma,  333 

Descendens  noni  nerve,  444 
Development,  15,  578 

relation  to  growth,  311 

of  organs,  593 

of  alimentary  canal,  606 

of  blood,  81 

of  bone,  49 

of  embryo,  578,  e.  s. 

of  extremities,  596 

of  face  and  visceral  arches,  595 

of  heart  and  vessels,  597 


INDEX. 


633 


Development  of  nervous  system,  603 
of  organs  of  sense,  603 
of  respiratory  apparatus,  608 
of  teeth,  53 

of  vascular  system,  597 
of  vertebral  column  and  cranium, 

594 

of  Wolffian  bodies,  urinary  appa- 
ratus and  sexual  organs,  609 
Dextrin,  formation  of  in  digestion,  230 
Diabetes,  269,  359 
Diaphragm,  88 

action  of  on  abdominal  viscera, 

182 

in  inspiration,  162 
in  various  respiratory  acts,  180, 

184 

in  vomiting,  232,  233 
Dicrotous  pulse,  129 
Diet,  influence  of  on  blood,  76 
Diffusion  of  gases  in  respiration,  171 

of  impressions,  385 
Digestion,  general  nature  of,  199 
of  food  in  the  intestines,  238 
of  food  in  the  stomach,  214,  222, 

223 
influence  of  nervous   system 

on,  234 

of  stomach  after  death,  236 
See  Gastric  Fluid,  Food,  Stomach. 
Digestive  fluid.     See  Gastric  Fluid, 
artificial,  224 

tract  of  mucous  membrane,  317 
Direction  of  sounds,  perception  of,  544 

of  vision,  515 
Discus  proligerus,  564 
Disease  in  relation  to  assimilation  and 

nutrition,  307 

in  relation  to  beat  of  body,  191 
Diseased  parts,  assimilation  in,  310 
Diseases,  alteration  of  blood  produced 

by, 307 
maintenance    of    alterations   by, 

310 

reflex  acts  in,  400 
Distance,  adaptation   of  eye  to,  510— 

512 

of  sounds,  how  judged  of,  544 
Distinctness  of    vision,  how  secured, 

508 

Dorsal  laminse,  582,  595 
Dorsum  of  tongue,  548 
Double  hearing,  545 

vision,  521 

Dreams,  phenomena  of,  422 
Dropsy,  serous  fluid  of,  contains  albu- 
men, 22 

Drowning,  cause  of  death  in,  187 
Duct,  cystic,  252,  262 
hepatic,  252,  257 
thoracic,  279,  286 


Duct,  vitelline,  584 

Ductless  glands,  325 

Ducts  of  glands,  arrangement  of,  319 

contraction  of,  324 
lactiferous,  613 
Ductus  arteriosus,  601 
venosus,  601 

closure  of,  602,  603 
Duodenum,  239 

Duration  of  impressions  on  retina,  517 
Duverney's  glands,  563 
Dysphagia,  absorption  from  nutritive 
baths  in,  348 


Ear,  527 

bones  or  ossicles  of,  529 
function  of,  538 

development  of,  605 

external,  527 

function  of,  534 

internal,  529 

function  of,  541 

middle,  527 

function  of,  536 

Ectopia  vesicse,  observations  on,  355 
Efferent  nerve-fibres,  376 

lymphatics,  286 

vessels  of  kidney,  352 
Eggs  as  articles  of  food,  201 
Eighth  cerebral  nerve,  435 
Elastic  cartilage,  43 

coat  of  arteries,  115 

fibres,  39 

recoil  of  chest  and  lungs,  165 

tissue  in  arteries,  115 
in  bronchi,  156 

tissues,  heat  developed  in,  190 
Elasticity,  of  arteries,  116 

employed  in  expiration,  165 
Electricity,  effect  on  nerves,  378 
Electro-magnetism,  effect  on  arteries, 
120 

on  rigor  mortis,  466 

on  voluntary  muscles,  464 
Elementary  substances  in  the  human 
body, 18 

accidental,  26 
Embryo.    See  Development  and  Foetus. 

formation  of  blood  in,  81 
Emission  of  semen  a  reflex  act,  399 
Emotions,  connection  of  with  cerebral 

hemispheres,  420 
Enamel  of  teeth,  51,  52 
End-bulbs,  337,  373 
End-plates,  motorial,  373 
Endolyrnph,  530,  533 

function  of,  541 
Endosmometer,  294 
Epidermis,  35,  333 

development,  <fcc. ,  of,  304 


634 


INDEX. 


Epidermis,  functions  of,  338 

hinders  absorption,  297 

nutrition  of,  308 

pigment  of,  333 

relation  to  sensibility,  338 

structure  of,  28,  35.  338 

thickening  of,  334 
Epididymis,  573 

Epiglottis,  action  in  swallowing,  213, 
214 

influence  of  on  voice,  481 
Epilepsy,  reflex  acts  in,  386 
Epithelium,  34 

ciliated,  38 

parts  occupied  by,   38.     See 
Ciliary  Motion. 

cylindrical  or  columnar,  35 

glandular,  35 

relation  to  gland-cells,  35,  319 

spheroidal,  35 

squaraous  or  tessellated,  34 

uses  of,  37 

of  air-cells,  159 

of  arteries,  115 

of  bronchi,  157 

of  bronchial  tubes,  358 

of  Fallopian  tubes,  561 

of  Graafian  follicles,  563 

of  hepatic  duct,  257 

of  intestinal  villi,  246 

absorption  by,  271,  291 

of  Lieberkuhn's  glands,  240 

of  mucous  membranes,  316 

of  olfactory  region,  495 

of  salivary  glunds,  209 

of  secreting  glands,  319 

of  serous  membranes,  315 

of  the  tongue,  551 

of  tubular  glands  of  stomach,  217 

of  tympanum,  528 

of  urine-tubes,  350 

in  bile.  260 

in  mucus,  24 

in  saliva,  209 

in  urine.  364 
Erect  position  of  objects,   perception 

of,  513 

Erectile  structures,  circulation  in,  152 
Erection,  153 

cause  of,  1 53 

influence  of  muscular  tissue  in, 
153 

of  penis,  connection  of  with  cere- 
bellum, 417 

a  reflex  act,  399 
Eunuchs,  voice  of,  484 
Eustachian  tube,  development  of,  606 

function  of,  540 

Excito- motor  and  sensori-motor  acts, 
398,  note 


Excreta  in  relation  to  muscular   ac- 
tion, 473 
Excretin.  274 
Excretoleic  acid,  274 
Excretion,  direct  ;md  indirect,  of  bile, 

264 

general  nature  of,  314 
Excretory    organs,     influence    of    on 

blood,  85,  155 

Exercise,  effects  of  on  muscles,  300 
on  nervous  tissue,  300 
on    production    of    carbonic 

acid,  176 

on  temperature  of  body,  197 
on  venous  circulation,  144 
undue,  increased  growth  from, 309 
Expansion  and  contraction  of  chest, 

162-165 
Expiration,  162 

influence  of  on  circulation,  146 
mechanism  of,  163 
muscles  concerned  in,  164 
relative  duration  of,  166 
Expired  air,  properties  of,  173 
Expression,    loss    of    in    paralysis    of 

facial  nerve,  434 

Expulsive  actions,  mechanism  of,  183 
Extractive  matters,  in  blood,  75 

in  urine,  364 

Extremities,  development  of,  596 
Eye,  499,  e.  s. 

adaptation  to  vision  at  different 

distances,  510-512 
capillary  vessels  of,  134 
development  of,  603 
effect  on,  of  injury  of  facial  nerve, 

434 

of  fifth  nerve,  309,  431 
movements  of,  427 
nerves,     supplying     muscles     of, 

425-427 

optical  apparatus  of,  507 
refracting  media  of,  505 
structure  of,  500 
Eyelids,  development  of,  605 
Eyes,    simultaneous  action   of   in  vi- 
sion, 521 


Face,  development  of,  595 

effect  of  injury  of  seventh  nerve 
on,  434 

influence  of  fifth  nerve  on,  429 
Facial  nerve,  433 

effects  of  paralysis  of,  434 

relation  of  to  expression,  434 
Faeces,  composition  of,  274 

quantity  of,  273 

result  of  examination  of,  228 
Fallopian  tubes,  560 

ciliated  epithelium  in,  37 


INDEX. 


635 


Fallopian-tubes,    opening    into  abdo- 
men. 315 

reflex  action  of,  400 
Falsetto  notes,  485 
Fasciae,  40 

Fasciculi  of  muscles,  458 
Fasciculus,  olivary,  404 

teres,  404 
Fasting,  influence  on  secretion  of  bile, 

261,262 

saliva  during,  2]0 
Fat,  action  of  bile  on,  265,  270 

of   pancreatic    secretion    on, 

251,  270 

of  small  intestine  on,  271 
situations  where  found,  40 
structure  of,  40 
uses  of,  41 

Fatty  acid,  volatile,  in  blood,  75 
Fatty  substances,  composition  and  de- 
scription of,  20 
absorbed  by  lacteals,  271 
in  relation  to  heat  of  body,  197 
of  bile,  259 
in  blood,  74 

use  of,  86 
of  chyle,  286 
Female  generative  organs,  560 

voice,  483 
Fenestra  ovalis,  530 

office  of,  540 
rotunda,  532 

office  of,  540 
Fermentation,     digestion      compared 

with,  225 
Ferments,  24 

Fibre-cells  of  involuntary  muscle,  456 
Fibres  of  MiilJer,  502,  504 

of  muscle,  involuntary,  456 

voluntary,  458.   See  Muscular 

Tissue. 

of  nerves.     See  Nerve-fibres, 
various  forms  of,  33 
Fibrils  or  filaments,  33 

muscular,  459 
Fibrin  in  blood,  74 

coagulating  principle  in,  58 
use  of,  86 
in  chyle.  288 

compared  with  albumen,  23 
formation  of,  6 1 
artificial,  23 
in  lymph,  286,  289 
sources  and  properties  of,  22 
vegetable,  202 
weight  in    blood  includes    white 

corpuscles,  74 

Fibrinopliistic  and  fibrinogenous  mat- 
ter, 62 

Fibrinoplastin,  62,  69 
Fibro-cartilage,  43 


Fibro-cartilage,  white,  45 

yellow,  45 
Fibrinogen,  62 
Field  of  vision,  actual  and  ideal  size 

of,  513 
Fifth     nerve,     428.       See     Cerebral 

Nerves. 
Filaments,  33 

seminal,  574 

Filiform  papillae  of  tongue,  548,  550 
Fillet,  404 

|  Filum  terminale,  388,  424 
Fimbriae  of  Fallopian  tube,  561 
Fingers,  development  of,  596 
Fish,  cerebella  of,  417 

temperature  of,  192 
Fissure  of  spinal  cord,  388 
Fistula,  gastric,   experiments  in  cases 

of,  220,  221,  223 
|  Flesh  compared  with  blood,  65 
Fluids,  passage  of  through  membranes, 

294 

Fluorin  in  animal  body,  25 
Focal  distance,  510 
Foetus,  blood  of,  81 

circulation  in,  601 
communication  with  mother,  591- 

593 

fseces  of,  263 
office  of  bile  in,  263 
pulse  in,  109 
Follicles,  Graafian,  563.   See  G-raafian 

Vesicles, 
of  hair,  340 
of  Lieberkiihn,  240 
Food,  199-205 

action  of  bile  on,  264 

of  gastric    fluid,    222,    223, 

225,  226 

of  pancreatic  secretion,  251 
of  pepsin,  mode  of,  225 
of  saliva,  211-213 
of  stomach,  231 
albuminous,  changes  of,  229,  251, 

271 
amylaceous,  changes  of,  212,  230, 

251,  271 

animal,  digestion  of,  226 
of  animals,  200 

calorifacient  or  respiratory,  202 
of  carnivorous  animals,  202 
changes  of  by  digestion,  chemi- 
cal. 229 
structural,  229 
in  large  intestines,  272 
in  mouth,  209 
in  small  intestines,  270-272 
in  stomach,  225-230 
classification  of,  199-200 
digestibility  of  articles  of,  228 
value  dependent  on,  207 


636 


INDEX. 


Food,  digestion  of,  in  intestines,  238 

in  stomach,  214 

eggs,  an  example  of  mixed,  201 
fatty  elements  of,  changes  of,  252, 

265 

general  purposes  of,  199 
of  herbivorous  animals,  202 
liquid,  absorption  of,  226.  271 
of  man,  202 
milk,  a  natural,  200 
mixed,  the  best  for  man,  205-207 
mixture  of,  necessary,  199-202 
nitrogenous  and  non-nitrogenous, 

199,  200 
oleaginous  principles  of,  changes 

in  stomach,  230 
passage   of    through    alimentary 

canal,  207 
into  stomach,  213 
relation  of  to  carbonic  acid  pro- 
duced, 176 

to  excretion,  205-207 
to  heat  of  body,  197 
to  muscular  action,  474 
of  gastric  fluid,  219 
of  saliva,  210 

relation  of  to  urea,  360,  361 
to  urine,  357 
phosphates  in,  365 
sulphur  in,  365 
saccharine  principles  of.  changes 

in  stomach,  230 
solid,  action   of  gastric  fluid  on, 

226 

swallowing  of,  213 
time  occupied  in  passage  of,  274 
vegetable,    contains    nitrogenous 

principles,  202 
changes  of  in  digestion,  225 
Foramen  ovale,  601 
Form  of  bodies,  how  estimated,  515 
Fornix,  office  of,  424 
Fourth  ventricle,  404,  419 

cerebral  nerve,  426 
Fovea  centralis,  501,  504 
Freezing,  effect  of  on  blood,  63 
Frequency  of  heart's  action,  108 
Functions  of  parts,  discharge  of,    at- 
tended   with     impairment    of 
tissue,  299,  300 
growth  from  undue  exercise  of, 

312 

Fundus  of  uterus,  562 
Fungiform  papillae  of  tongue,  548,  549 


Galactopborous  ducts,  613 
Gall-bladder,  passage  of  bile  into  and 

from,  262 
Ganglia,  mode  of  action.   See  Nervous 

Centres 


Ganglia,   cerebral    or   sensory,    func- 
tions of,  411 

of  spinal  nerves,  391,  444 
of  the  sympathetic,  445 
structure  of,  447 
action  of,  450 

as  co-ordinators  of  involun- 
tary movements,  451 
in  heart,  114 

in  substance  of  organs,  451 
Ganglion,  Gasserian,  428,  445 

corpuscles,  375,  447.     See  Nerve- 
corpuscles. 

Ganglionic  fibres,  391 
Ganglionic  nervous  system.    See  Sym- 
pathetic Nerves. 

Gases,  absorption  of  by  blood,  296 
absorbed  by  the  skin,  348 
in  blood,  81 

in  stomach  and  intestines,  274 
in  urine,  367 
Gastric  fluid,  219 
acid  in,  222 

action    of    on   albuminous    prin- 
ciples, 229 
on  food,  226-230 
favored  by  division,  226 
nature  of,  225 

on  saccharine  and  amylace- 
ous principles,  230 
artificial,  224 
characters  of,  221 
composition  of,  222 
digestive  power  of,  222 
experiments  with,   223-224,  226- 

230 

pepsin  in,  222 
quantity  of,  220 
secretion  of,  220 

how  excited,  220,  221 
influence  of  nervous  system 

on,  235 

Gastric  veins,  blood  of,  79 

Gelatinous  substances,  21 

Gelatin,  digestion  of,  229 

insufficient  as  food,  202 

properties  of.  21 

Generation  and  development,  559 
Generative  organs  of  the  female,  560 
Genito-urinary  tract  of  mucous  mem- 
brane, 317 
Germinal  area,  581 
matter,  27 
membrane,  581 
spot,  565 

development  of,  565 
vesicle,  565 

development  of,  566 
disappearance  of,  579 
Gizzard,  action  of,  231 
Gland,  pineal,  424 


INDEX. 


637 


Gland,  pituitary,  424 

prostate,  573,  577 
Gland-cells,  agents  of  secretion,  319 

relation  to  epithelium,  35,  319 
Gland-ducts,  arrangement  of,  321 

contractions  of,  323 
Glands,  aggregated,  319 

Brunn's,  245 

ceruminous,  339 

conglomerate,  319 

Cowper's.  573,  577 

ductless,  325,  326 

Duverney's,  563 

of  large  intestine,  249 

lenticular  of  intestine,  249 
of  stomach,  219 

of  Lieberkuhn,  240 

lymphatic.         See        Lymphatic 
Glands. 

of  Peyer,  241 

mammary,  613 

salivary,  209 

sebaceous,  339 

secreting.     See  Secreting  Glands. 

of  small  intestine,  239 

of  stomach,  217 

sudoriparous,  338 

tubular,  319 

of  large  intestine,  249 
of  stomach,  217 

vascular,      325.     See      Vascular 
Glands. 

vulvo-vaginal.  563 
Glandulse  Nabothi,  562 
Glandular  epithelium,  35 
Glisson's  capsule,  253 
Globulin,  69 

Globus  major  and  minor,  573 
Glosso-pharyngeal  nerve,  435 

communications  of,  435 

motor  filaments  in,  436 

a  nerve  of  common  sensation  and 

of  taste,  437,  553 

Glottis,  action   of  laryngeal  muscles 
on,  479,  480 

closed  in  vomiting,  183,  232 

effect  of  division  of  pneumogastric 
nerves  on,  441 

forms  assumed  by,  480 

narrowing    of,     proportioned    to 
height  of  note,  481 

respiratory  movements  of,  166 
Glucose  in  blood.  75 
Gluten  in  vegetables,  202 
Glycocholic  acid,  259 
Glycogen  orglycogenic  substance,  267 
Glucose,  268 
Graafian  vesicles,  563 

formation    and   development    of, 

563,  567,  570 
•     constant,  567 


Graafian  vesicles,  relation  of  ovum  to, 
563,  566 

rupture  of,  changes  following,  570 
Granular  layer  of  retina,  502 
Granules,  29.      See  Molecules. 
Grape-sugar  in  blood,  75 
Gray  matter  of  cerebellum,  415 

of  cerebral  ganglia,  412 

of  cerebrum,  420 

of  crura  cerebri,  409 

of  medulla  oblongata,  402 

of  pons  Varolii,  409 

of  spinal  cord,  388 

functions  of,  393,  394 
Groove,  primitive,  582 

primitive  dental,  53 
Growth,  311 

coincident  with  development,  14, 
311 

compared  with  common  nutrition, 
313 

conditions  of,  313 

continuance  of,  311 

as  hypertrophy.  312 

increased  by  increase  of  function, 
312 

not  peculiar  to  living  beings,  14 
Gum,  insufficient  as  food,  201 
Gustatory  nerves,  437,  552 


Habitual  movements,  400 
Hsetnatin,   71 
Haemadynamometer,  129 

experiments  on  respiratory  power 

with,  169 

Hsemodrometer,  131 
Haemoglobin,  68,  77,  180 
Hair,  340 

casting  of,  302 

chemical  composition  of,  24 

development  and  growth  of,  301 

growth  near  old  ulcers,  313 

structure  of,  340 
Hair-follicles,  340 

their  secretion,  343 
Halitus  or  odor  of  blood,  56 
Hamulus,  532 
Hand,  principal  seat  of  sense  of  touch, 

555 

Haversian  canals,  48 
Hearing,  anatomy  of  organs  of,  527 

double,  545 

impaired  by  lesion  of  facial  nerve, 
434 

influence  of  external  ear  on,  540 
of  labyrinth,  541-543 
of  middle  ear,  536-541 

physiology  of,  534 

See  Sound,  Vibrations,  Ac. 
Heart,  91-114 


54 


638 


INDEX. 


Heart,  action  of,  96 

effects  of,  114 
force  of,  110 
frequency  of,  108 
after  removal,  112 
rhythmic,  111 
weakened  in  asphyxia,  186 
auricles  of,  91 

their  action,  96 

See  Auricles, 
chordae  tendineae  of,  94 
columnse  carneoe  of,  94 
course  of  blood  in,  91 
development  of,  597 

of  cavities  and  septa,  599 
fleshy  columns  of,  94 

action  of,  98 
ganglia  of,  112 
hypertrophy  of,  312 
impulse  of,  108 
influence  of  pneumogastric  nerve, 

111,  438,  439 
of   sympathetic  nerve,  112,   451, 

452 

muscular  fibres  of,  461 
nervous   connections  with    other 

organs,  114 
sounds  of,  105 
first,  105 

in  relation  to  pulse,  135 
second,  106 
structure  of,  91 
tendinous  cords  of,  94 
valves  of,  their  action,  99 
arterial  or  semilunar,  96 

action  of,  102 
auriculo-ventricular,  94 

action  of,  100 
ventricles  of,  their  action,  97 

capacity,  111 

Hearts,  lymphatic.   See  Lymph-hearts. 
Heat,  action  of  on  nerves,  378 

animal,  189.     See.  Temperature, 
adaptation  to  climate,  191 
connection   of   with   respira- 
tion, 192-196 
influence  of  age  on,  189 
of  exercise,  190 

of    external     coverings, 

197 

of  food,  197 
of  nervous  system,  198 
losses  by  radiation,  &c.,  194 
in  relation  to  bile,  263 
sources  and  modes  of  produc- 
tion, 192 

developed  in  contraction  of  mus- 
cles, 190,  463 
perception  of,  559 
Heat  or  rut,  568 

analogous  to  menstruation,  569 


Height,  relation  to  respiratory  capa- 
city, 167 
Helicotrema,  532 
Helix  of  ear,  527 

Hemispheres,  cerebral.   See  Cerebrum. 
Hepatic  cells,  253 

ducts,  252,  257 

veins,  255 

characters  of  blood  in,  80 

vessels,  arrangement  of,  253 
Hepatin,  267 
Herbivorous    animals,    perception    of 

odors  by,  498 

Henna phroditism,  apparent,  613 
Hibernation,  retarded  respiration,  <fec., 
during,  189 

state  of  thymus  in,  330 

temperature  in,  194 
Hiccough,  mechanism  of,  182 
Hilus  of  kidney,  350 

spleen.  327 

Hip-joint,  pain  in  its  diseases,  384,  395 
Hippuric  acid  in  blood,  76 

in  urine,  463 
Horny  matter,  chemical   composition 

of,  24 

Horse's  blood,  peculiar  coagulation  of, 
68 

cerebellum,  417 
Hunger,  sensation  of,  234 
Hyaline  cartilage,  44 
Hydrochloric  acid  in  gastric  fluid,  222 
Hydrophobia,  spasms  of,  386 
Hygrometric    conditions    influencing 

respiration,  176 
Hymen,  562 
Hypertrophy,  312 
Hypoglossal  nerve,  444 
Hypospadias,  613 


Ideas,  connection  of  with    cerebrum, 

420 

Ileum,  239 
Ileo-csecal  valve,  238,  248 

structure  and  action,  250,  276 
Image,  formation  of  on  retina,  507 
distinctness  of,  508 
inversion  of,  512 
Impressions,  retained  and  reproduced 

in  cerebrum,  420 
Impulse  of  heart,  107 
Incus,  529 

function  of,  539 
Inflammatory  blood,  coagulation  of, 

64 

corpuscles  in,  68 
Infundibulum,  158 
Inhibitory  influence  of  pneumogastric 

nerve,  113 
Inhibitory  nerves,  377 


INDEX. 


639 


Inorganic  elements  in  human  body,  25 
Insects,  temperature  of,  193 
Inspiration,  162 

elastic  resistance   overcome    by, 

170 

force  employed  in,  169 
during  apnoea,  170 
influence  of  on  circulation,  146 
mechanism  of,  162 

Instability  of  organic  compounds,  19 
Intellectual  faculties,  relation  to  cer- 
ebrum, 420 

Interarticular  fibro-cartilage,  45 
Intercellular  substance,  32 
Intercostal  muscles,  action  in  inspira- 
tion, 162 

in  expiration,  165 
Interlobular  veins,  254 
Intestinal  canal,  development  of,  585, 

605 

Intestines,  digestion  in,  238 
fatty  discharges  from,  252 
gases  in,  274 
large,  digestion  in.  272 
glands  of,  249 
structure  of,  248 
movements  of,  275 
small,  changes  of  food  in,  270 
glands  of,  240 
structure  of,  238 
valvulae  conniventes  of,  240 
villi  of,  246 
Intonation,  488 
Intralobular  veins,  254 
Inversion  of  images  on  retina,  512 

correction  of,  513 
Involuntary  movements  originated  by 

will,  413 
muscles,  action  of,  473 

structure  of,  456 
Iris;  506 

action  of,  426,  509 

in   adaptation  to    distances, 

511 

capillaries'of,  134 
development  of,  605 
influence  of  fifth  nerve  on,  430 
of  sixth  nerve,  427 
of  third  nerve,  426,  note. 
relation  of  to  optic  nerve,  425 
structure  and  function  of,  507 
Iron  in  parts  of  body  in  which  found, 

26 

Irritability  of  muscular  tissue,  461 
Iter  a  tertio  ad  quartum  ventriculum, 

419 
Ivory  of  teeth,  51 


Jacob's  membrane,  502 
Jacobson's  nerve,  435 


Jejunum,  239 

Jetting  flow  of  blood  in  arteries,  118 

Jumping.  472 


Keratin,  24 

Kidney,    increased   function    of    one, 

324 
Kidneys,  their  structure,  349 

bloodvessels  of,  how   distributed, 

352 

capillaries  of,  135,  353 
development  of,  609 
function  of,  354.     See  Urine. 
Malpighian  bodies  of,  352 
tubules  of.  350 

Knee,   pain  of,   in   diseased  hip,  384, 
395 


Labia  externa  and  interna,  563 
Labyrinth  of  the  ear.  529 

membranous,  532 

osseous,  529 

function  of,  541 
Lacteals,  279 

absorption  by,  290 

contain  lymph  in  fasting,  288 

origin  of,  280 

structure  of,  282 

in  villi,  248,  291 
Lactic  acid  in  blood,  76 

in  gastric  fluid,  222 
Lactiferous  ducts,  613 
Lacunae  of  bone,  48 
Lamellae  of  bone,  48,  49 
Lamina  spiralis,  532 

use  of,  542 
Laminae  dorsales,  582,  595 

viscerales  or  ventrales,  582,  595 
Language,  how  produced,  486 
Large  intestine.     See  Intestine. 
Laryngeal  nerves,  438 
Larynx,  construction  of,  476 

influence  of  pneutnogastric  nerve 
on,  439-441 

irritation  referred  to,  384 

muscles  of,  479 

variations  in  according  to  sex  and 
age,  484 

ventricles  of,  486 

vocal  cords  of,  476,  479 
Laws  of  functions  of  nerves,  382 
Laxator  tympani  muscle,  529 
Lead  an  accidental  element,  26 
Leaping,  472 

Legumen  identical  with  casein,  203 
Lens,  crystalline,  506 
Lenticular  ganglion,  relation  of  third 

nerve  to,  425 
Lenticular  glands  of  stomach,  219 


640 


INDEX. 


Lenticular  glands  of  large  intestine, 

249 

Leucocytes,  71 
Leucocytbaemia,    state    of     vascular 

glands  in,  331 
Levator    palpebrae    superioris,    nerve 

supplying,  425 

Levers,  different  kinds  of,  467 
Lieberkuhn's    glands,     in    large    in- 
testines, 249 
in  stomach,  240 
Life,  animal,  367 

dependence  of  on  medulla  oblon- 

gata,  405 
natural  term  of,  for  each  particle, 

304 

organic,  368 

simplest  manifestation  of,  13 
Lightning,   condition    of  blood    after 

death  by,  64 

Lime,  salts  of,  in  human  body,  26 
phosphate  of,  in  albumen,  22 
in  blood,  26 

in  bones  and  teeth,  26,  46 
in  tissues,  26 
Lingual    branch  of  fifth   nerve,    431,  j 

432,  437,  553 
Lips,  influence  of  fifth  nerve  on  move-  j 

ments  of,  429 
Liquid    part    of  food,    absorption  of, 

226,  271 

Liquor  ainnii.  586 
Liquor  sanguinis,  55,  58 

lymph  derived  from,  291 
still  layer  of  in  capillaries,  137 
Lithium,  absorption  of  salts  of,  297 
Liver,  252 

action  of  on  albuminous  matters, 

266 

on  saccharine  matters,  266 
a  blood-making  organ,  90 
bloodvessels  of,  255-258 
capillaries  of,  134,  135 
cells  of,  254 
circulation  in,  90 
development  of,  607 
ducts  of,  258 
functions  of,  259 

in  foetus,  263 

glycogenic  function  of,  267 
secretion  of,  259.     See  Bile, 
structure  of,  252 
sugar  formed  by,  267-269 
test  for  presence  of  sugar  in,  267 
Living  bodies,  properties  of,  13 

tissues,   contact  with  retards  co- 
agulation, 62 
Lobes  of  lungs,  158 
Lobules  of  liver,  258 

of  lungs,  158 
Locus  niger,  411 


Love,  physical,  cerebellum,   in   rela- 
tion to, 417 

Luminous  circles   produced   by  pres- 
sure on  eyeball,  522 
impressions,  duration  of,  517 
Lungs,  155,  159 

capillaries  of,  134 
cells  of,  158-161 
changes  of  air  in,  171 
circulation  in,  89,  172 
congestion  of,  in  asybyxia,  187 
after  division  of  pneumogas- 

tric  nerve,  441 
contraction  of,  165 
coverings  of,  156 
development  of,  609 
elasticity  of,  165 
intercellular  passages  in,  159 
lobes  of,  158 
lobules  of,  158 
movements  of  in  respiration,  161— 

166 

nutrition  of,  172 
position  of,  155 
structure  of,  155,  158 
supplied  by  pneumogastric  nerve, 

438,  439 
Lymph,  analysis  of,  288 

compared  with  chyle,  288 

with  blood,  289 
general  characters  of,  286 
quantity  formed,  290 
relation  to  blood,  289,  292 
Lymph-corpuscles,  structure  of,  286 
in  blood,  83 

development    into    blood-corpus- 
cles, 83 
Lymph-hearts,  structure   and    action 

of,  292  . 

relation   of  to  spinal  cord,  293, 

401 
Lymphatic  glands,  structure  of,  283 

function  of,  286 
Lymphatic    vessels,     absorption    by, 

291 

communication  with  serous  cavi- 
ties, 280 
communication  with  bloodvessels, 

286 

contraction  of,  283 
course  of  fluid  in,  278  ' 
distribution  of,  280 
origin  of,  280 

propulsion  of  lymph  by,  282 
structure  of.  277,  282 
valves  of,  282 

Lymphoid  tissue.     See  Betiform  Tis- 
sues. 

Macula  germinativa,  565 
Magnesium  in  human  body,  26 


INDEX. 


641 


Maintenance  or  assimilation,    nature 

of  the  process.      See  Growth, 
nutritive,  299 
of  blood,  84 
Male  sexual  functions,  573 

voice.  483 
Malleus,  529 

function  of,  539 
Malpighian  bodies,  350,  352 

capsules.  350-353 
Mammary  glands,  613 
Manganese,  an  accidental  element,  26 
Marginal  fibro-cartilages,  45 
Marrow  of  bone,  46 
Mastication,  209 

fifth    nerve   supplies  muscles    of, 

428 

Mastoid  cells,  528 
Matrix  of  cartilage,  43 

of  nails,   341 
Meatus  of  ear,  527 

urinarius,   opening  of  in  female, 

563 
Mechanical  irritation,  violent,   effect 

on  nerves,  378 

Meconium,  biliary  principles  in,  263 
Medulla  of  bone,  46 

of  hair,  340 

Medulla  oblongata,  402,  409 
analogy  to  spinal  cord,  405 
columns  of,  403 

distribution  of  fibres  of,  404 
conduction  of  impressions  in,  405 
congested  in  asphyxia,  186 
decussation  of  fibres  in,  404,  405 
development  of,  603 
effects   of  injury  arid   disease   of, 

406 

fibres  of,  how  distributed,  404 
functions  of,  405 
important  to  maintenance  of  life, 

405 
influence  on  deglutition,  407 

on  respiration,  185,  406,  408 
on  speech,  408 

maintenance  of  power  in,  408 
as  a  nerve-centre,  405 
pyramids  of,  anterior,  404 

posterior,  405 
reflecting  power  of,  406 
sensation    and    voluntary    power 

not  seated  in,  408 
structure  of,  402 
Medullary  portion  of  kidney,  350 

substance    of  lymphatic    glands. 

283 

substance  of  nerve -fibre,  369 
Membrana  decidua,  591 
granulosa.  563 

development  of   into  corpus 
luteum,  672 


Membrana  lituitanp,  502 

propria.        See      Basement-mem- 
brane. 

pupillaris,  605 
capsulo-pupillaris,  605 
tympani,  527 

office  of,  537,  539 
Membrane,   blastodermic,  581 
Jacob's,  502 
ossification  in,  50 
primary  or  basement.     See  Base- 
ment-membrane, 
vitelline,  564,  579 
Membranes,     mucous.       See.    Mucous 

Membranes. 
Membranes,     serous.        See      Serous 

Membranes. 
Membranes,  passage  of  fluids  through, 

294 

secreting,  314 

Membranous  labyrinth,  529,  532 
Memory,    relation   to  cerebral   hemi- 
spheres, 420 
Menstruation,  568 

analogous  with  heat,  569 
coincident  with  discharge  of  ova, 

568 

corpus  luteum  of,  571 
phenomena  of,  569 
time  of  appearance  and  cessation, 

569 
Menstrual  discharge,  composition  of, 

569 
Mental  derangement,  421 

exertion,  effect   on  heat  of  bod}', 

198 

on  phosphates  in  urine,  366 
faculties,  development  of  in  pro- 
portion to  brain,  420 
theory  of  special  localization 

of,  421-424 
field  of  vision,  514 
Mercury,  absorption  of,  298,  347 
Mesenteric    arteries,    contraction    of, 

120 

veins,  blood  of,  79 
Meshes  of  capillary  network,  134 
Mesocephalon,  409 
Metallic  substances,  absorption  of  by 

skin,  347 

Mezzosoprano  voice,  483 
Micturition,  action  of  spinal  cord  in, 

399 
Milk,  as  food,  200 

properties  of.  615 
secretions,  614 
Milk-globules.  615 
Milk-teeth,  54 
Mind,  cerebral  hemisphere  the  organs 

of,  420-422 
influence  on  action  of  heart,  111 


642 


INDEX. 


Mind,  influence  on  animal  heat,  198 
on  digestion,  228,  236 
on  hearing,  544 
on  movements  of  intestines, 

277 

on  nutrition,  306 
on  respiratory  acts,  185,  236 
on  secretion,  324 
on  secretion  of  saliva,  211 
in  taste,  553 
in  touch,  555 
in  vision,  513-518 
perception   of  special    sensations 

by,  489 

independently  of  organs,  491 
perception  of  transferred  impres- 
sions, 384,  385 
power   of    concentration   on    the 

senses,  516 

of  exciting  sensations,  559 
reflex  movements  independent  of, 

395 
sensitive  impressions  referred  to 

parts  by,  381 
Mitral  valve,  92 
Mixed  food  for  man,  205 

necessity  of,  200 
Modiolus,  531 
Molecules,  or  granules,  29 
in  blood,  72 
in  milk,  615 
movement  of  in  cells,  32 
Molecular  base  of  chyle,  287 

motion,  29 

Monotonous  voice,  483 
Mortification   from    deficient    blood, 

307 

Motion,  causes  and  phenomena  of,  454 
ciliary,  454.     See  Cilia, 
molecular,  29 
muscular,  456 

action  on  bones  as  levers,  467 
nerves  of,  377 

of  objects,  how  judged,  516 
power  of,  not  essentially  distinc- 
tive of  animals,  16 
sensation  of,  492 
Motor   impulses,   transmission    of   in 

cord,  395 
nerve-fibres,  377 
nerves,  cranial,  425 

laws  of  action  of,  382 
roots  of  spinal  nerves,  390,  444 
Motor  linguae  nerve,  444 

oculi,  or  third  nerve,  425 
Motorial  end-plates,  373 
Mouth,  changes  of  food  in,  207 
moistened  with  saliva,  211 
Movements  of  intestines,  275 
of  muscles,  467 

habitual,  400,  413 


Movements   of  muscles,    reflex.     See 

Reflex  Actions, 
sensation  of,  557 
symmetrical,  427 
produced  by  irritation  of  auditory 

nerve,  446 
of  respiration,  166 
of  stomach,  231 

Mucous  layer  of  blastodermic   mem- 
brane, 581 
Mucous  membranes,  316 

basement-membrane  of,  318 
capillaries  of,  134 
component  structures  of,  318 
epithelium-cells  of,  318.     See  Epi- 
thelium. 

gland-cells  of,  318 
tracts  of,  317 
of  intestines,  239,  249 
of  stomach,  215 
of  tongue,  548 

of   uterus,    changes    of   in    preg- 
nancy, 589 
Mucus,  nature  of,  24 
acid,  of  vagina,  56 
in  bile,  259 

of  mouth,  mixed  with  saliva,  209 
in  urine,  364 

Multipolar  nerve-cells,  375 
Muscles  of  animal  life,  458 
assisting  erection,  154 
assisting  vomiting,  232 
changes  in,  by  exercise,  300 
contraction  of,  461 
effect  of  pressure  of,  on  veins,  143 
heat  developed  in  contraction  of, 

463 

involuntary,  456 
moving  eyeball,  425 

larynx,  479 
nerves  of,  461 
nutrition  of,  308 
of  organic  life,  458 
sensibility  of,  461 
sound    developed   in    contraction 

of,  464 

source  of  action  of,  473 
striated,  458,  461 
voluntary,  458 
action  of,  467 
bloodvessels   and    nerves   of, 

461 

work  of,  how  estimated,  474 
Muscular  coat  of  arteries,  115,  118 
of  large  intestine,  249 
of  small  intestine,  238 
of  stomach,  215 
fibres,  involuntary,  456 
voluntary,  458 
of  stomach,  action  of,  231 
of  villi  in  intestines,  248 


INDEX. 


643 


Muscular  force,  idea  of,  how  derived, 

557 

motion,  456 

movements.     See  Movements, 
sense,  461,  556 

cerebellum  the  organ  of,  416 
strength    tested     by    respiratory 

efforts,    169 

tissue,  of  animal  life,  458 
in  arteries,  115 
contractility  of,  461 
contraction  of,  462 

heat  developed  in,  463 
sound  in, 463 

effect  of  stimuli  on,  377,  463 
of  heart,  460 
involuntary,  456 
irritability  of,  461 

duration  of,  after  death, 

464 

of  organic  life,  458 
properties  of,  461 
rigidity  of,  after  death,  465 
sensibility  of,  461 
striped,  458 

structure  of,  458-460 
unstriped,  456,  457 

situations  where  found, 

457 

structure  of,  457 
in  veins,  141 
tone,  402 

Muscularis  mucosae,  216,  239.  247,  248 
Muscularity,  of  arteries,  119 
evidence  of,  120 
purposes  of,  121 
of  lymphatics,  282 
of  lymph-hearts,  293 
Musical  sounds,  483 
Myopia  or  short-sigh  tadness,  512 
Myosin,  23 


Nabothi  glandulae,  562 

Nails,  chemical  composition  of,  24 

structure  of,  341 

growth  of,  343 

Narcotic  poisons  in  stomach,   experi- 
ments on, 235 

Nasal  cavities  in  relation  to  smell. 496 
Nates  (brain),  409 
Natural  organic  compounds,  19 

classification  of,  20 
Nerve,  depressor,  442 
Nerve-centres,  368.     See  Cerebellum, 
Cerebrum,  &c. 

conduction  in  or  through,  383 

congestion  of  in  asphyxia,  188 

diffusion  or  radiation  in,  385 

functions  of,  382 

perception  in,  383 


Nerve-centres,  reflection  in,  385 

conditions  of,  385 
transference  of  impressions  in, 384 
vaso-motor,  452 
Nerve-corpuscles,  375 

caudate  or  stellate,  375 
of  retina,  504 
simple,  375 
•  Nerve-fibres,  369-382 

axis-cylinder  of,  370 
cerebro-spinal,  369 
conduction  of  impressions  by,  378 
of  one  kind  only,  379 
rate  of,  479 
continuity  of,  372 
course  of,  372 

difference  in  function  not  attended 

by  difference  of  structure,  377 

effects  of  injury  and  division,  380, 

382 

fasciculi  of,  372 
force  not  generated  by,  377 
functions  of,  376 

effect   of   chemical   stimula- 

tion,  378 
of  mechanical  irritation, 

378,  380 

of  temperature,  378 
impressions  on,  referred  to  periph- 
ery, 381 
kinds  of,  369 
laws  of  action,  378 

of  motor  nerves,  382 
of  sensitive  nerves,  379 
medullary  or  white  substance  of, 

370 

plexuses  of,  372 
of  retina,  504 
size  of,  370 
structure  of,  369 
sympathetic,  271 
terminations  of,  373 
in  cells,  373 
in  free  ends,  373 
in  motorial  end -plates,  373 
in  networks  or  plexuses,  373 
in  special    terminal    organs, 

373 

Nerves,  action  of  stimuli  on,  377,  378 
afferent,  376 
centrifugal,  376 
centripetal,  376 
cerebral,  physiology  of,  424.    See 

Cerebral  Nerves. 
efferent,  376 
excito-vaso-motor,  453 
inhibitory,  113,  377 
of  motion,  or  motor,  377 

laws  of  action  in,  382 
respiratory,  185 
of  sensation  or  sensitive,  377 


644 


INDEX. 


Nerves   of  sensation,  laws   of  action 

in,  379 

of  special  sense,  424 
secretory,  325,  377 
spinal,  390.     See  Spinal  Nerves, 
stimuli  of,  377 
structure  of,  269 
sympathetic.       See    Sympathetic 

Nerve. 

trophic,  310,  377 
ulnar,  effect  of  compression  of,  380 

of  division  of,  382 
vaso-inhibitory.  453 
vaso-motor,  121,  452 
Nervi-nervorum,  381 
Nervous  force,  velocity  of,  386 

layer  of  retina,  504 
Nervous  substance,  chancres  in  from 

mental  exertion,  377 
fibrous,  369 

phosphorus  in  urine  from,  365 
vesicular,  368,  375 
Nervous  system,  367 

eerebro-spinal,  367.  386 
development  of,  582,  603 
elementary  structure  of.  368.   See, 
Nerve-corpuscles    and    Nerve- 
fibres. 

influence  of  on  animal  heat,  198 
on  arteries,  122 
on  contractility,  461 
on   contraction   of  bloodves- 
sels, 122,  453 
on  erection,  153 
on  gastric  digestion,  234 
on  the  heart's  action,  112 
on  movements  of  intestines, 

376 

of  stomach,  236 
on  nutrition,  307 
on  respiration,  185 
on  secretion,  324 
on  sphincter  ani,  376 
of  organic  life,  368,  445 
sympathetic,  368 
Nervus    abducens    seu    ocularis    ex- 

ternus,  426 

patheticus  seu  trochlearis,  426 
vagus,  438.     See  Pneumogastric. 
Networks,  capillary,  133.      See  Capil- 
laries. 

Neuralgia,  division  of  nerves  for,  380 
New-born  animals,  heat  of,  190 
Ninth  cerebral  nerve,  544 
Nipple,  an  erectile  organ,  153 

structure  of,  614 
Nitrogen  in  blood,  81 

influence  of  in  decomposition,  20 
in  relation  to  food,  205 
in  respiration,  177 
Nitrogenous  food,  199,  202 


Nitrogenous  food,  in  relation  to  mus- 
cular work,  474 
in  relation  to  urea,  361 

to  uric  acid,  362 
principles,  21 
N*oise,  how  produced,  543 
Noises  in  ears,  546 
Nose.     See  Smell. 

irritation  referred  to,  384 
restoration  of,  sensitive  phenom- 
ena in,  381 
Non-azotized  or  non-nitrogenous  food, 

200 

organic  principles.  20 
Non-vascular  parts,  nutrition  of,  307 
Nuclei,  description  of,  29 

in  developing  and  growing  parts, 

305 

Nucleoli  or  nucleus-corpuscles,  29 
Nutrition   compared    with    secretion, 

322 

conditions  necessary  to,  306 
exiimples  of,  300 
general  nature  of,  299 
influence  of   conditions  of  blood 

on,  306 
of  nervous   system   on,   308, 

431 

of  state  of  part  on,  310 
of  supply  of  blood  on,  307 
of  sympathetic  nerves  on,  452 
in  paralyzed  parts,  308 
in      vascular     and    non-vascular 

parts,  307 
Nutritive,  repetition,  305 

reproduction,  305 
Nymphse,  563 


Oblique  muscles  of  the  eye,  action  of, 

427 
Ocular  cleft,  604 

spectrum,  517 
Odors,  causes  of,  495 

different  kinds  of  498 
perception  of,  494 

varies  in  different  classes,  498 
relation  to  taste,  553 
(Esophagus,  action  of  in  deglutition, 

214 

reflex  movements  of,  395 
Oil,  absorption  of,  291,  298 
Oily  matter,  20 

coated  with  albumen,  314 
Oleaginous    principles,    digestion   of, 

230,  251,  265,  270 
Olein,  20 
Olfactory  cells,  495 

lobes,  functions  of,  411 
nerve.  495 

subjective  sensations  of,  498 


INDEX. 


645 


Olivary  body,  403 

fasciculus,  404 
Ophthalmic  ganglion,  relation  of  third 

nerve  to,  425 
Optic   lobes,    corpora    quadrigemina, 

hoiuologues  of,  411 
functions  of,  411 
nerve,  decussation  of,  524 
fibres  of,  377 
point  of  entrance  insensible 

to  sight,  520 

thalamus,  function  of,  411 
vesicle,  primary,  603 

secondary,  604 
Optical  angle,  514 
Ora  serrata  of  retina,  501 
Oral  canal  and  oral  opening,  488 
Organic  compounds,  instability  of,  19 
peculiarities  of  some,   18 
processes,     influence    of    sympa- 
thetic nerve  upon,  450 
Organization,  definition  of,  18 
Organs,  plurality  of  cerebral,  421 
Organs  of  sense,  development  of,  603 
Os  orbiculare,  529 
Os  uteri,  562 
Osmosis,  294 
Osseous  labyrinth,  529 
Ossicles  of  the  ear,  529 

office  of,  537 
Ossification,  50 
Ossicula  auditus,  529 
Otoconia  or  Otolithes,  533 

use  of,  541 
Ovaries,  560 

enlargement  of  at  puberty,  567 
Graafian  vesicles  in,  563 
Ovisacs,  563 
Ovula  Nabothi,  562 
Ovum,  564 

action  of  seminal  fluid  on,  578 
changes  of  in  ovary,  566 

previous  to  formation  of  em- 
bryo, 578 

subsequent  to  cleaving,  581 
in  uterus,  581 
cleaving  of  yelk,  579 
connection  of  with  uterus,  588 
discharge  of  from  ovary,  567 
formation  of,  566 
germinal  membrane  of,  581 
germinal  vesicle  and  spot  of,  565 
impregnation  of,  573 
structure  of,  564 

Oviduct,  or  Fallopian  tube,  560,  561 
Oxalic  acid  in  urine,  367 
Oxygen,  in  blood,  81,  180 

consumed  in  breathing,  173,  177 
effects  of  on  color  of  blood,  77 
on     pulmonary    circulation, 
140 


Oxygen,  proportion  of  to  carbonic  acid, 

177 

union  with  carbon  and  hydrogen, 
producing  heat,  192 


Pacinian  bodies  or  corpuscles.  373 
Pain  excited  by  the  mind,  559 

in  paralyzed  parts,  380 
Palate  in  relation  to  deglutition,  213 

nerves  of,  439 
Palate  and  uvula  in  relation  to  voice, 

486 

Palmitin,  20 
Pancreas,  250 

development  of,  607 
functions  of,  250 
Pancreatic  fluid,  250 
Pa,ncreatin,  251 
Papilla},  of  the  kidney,  350 

of  skin,  distribution  of,  334 
end-bulbs  in,  337,  338 
epithelium  of,  337 
nerve-fibres  in,  336 
supply  of  blood  to,  336 
touch  corpuscles  in,  336 
of  teeth,  53 
of  tongue,  548 

circumvallate  or  calyciform, 

548 

of  tongue,  conical  or  filiform,  550 
fungiform,  549 
use  of,  552 
Paraglobulin,  69 
Par     vagum.        See     Pneumogastric 

Nerve. 
Paralyzed  parts,  pain  in,  380 

nutrition  of,  308 
limbs,  temperature  of,  198 
preservation  of  sensibility  in,  381 
Paralysis,  cross,  405 

seat  of,  according  to  part  of  cere- 

bro-spinal  axis  injured,  392 
Paraplegia,  delivery  in,  400 

influence  of  spinal  cord  shown  in, 

392 

reflex  movements  in,  396 
state  of  intestines  in,  277 
Parotid  gland,  saliva  from,  210 
Particles,  changes  of  in  nutrition,  299 
duration  of  life  in  each,  304 
natural  decay  and  death,  300 
process  of  forming  new,  305 
removal  when  impaired  or  effete, 

300 

Parturition,  mechanism  of,  183 
Patheticus,  or  fourth  nerve,  426 
Pause  in  heart's  action,  105,  106 

respiratory,  166 

Peduncles  of  the  cerebellum,  414 
of  the  cerebrum,  419 


646 


INDEX. 


Pelvis  of  the  kidney,  350 
Penis,  corpus  cavernnsum  of,  153 

development  of,  613 

erection  of,  explained,  153 

reflex  action  in,  153,  399 
Pepsin,  23,  222 
Peptone,   229 
Perception  of  sensations   by  cerebral 

hemispheres,  383,  420 
Perichondriuin,  43 

Perilymph,  or  fluid  of   labyrinth   of 
ear,  533 

use  of,  541 
Periosteum,  47 

Peristaltic  movements  of   intestines, 
376 

of  stomach,  231 
Permanent  cartilage,  43 

teeth,  52 
Perspiration,  cutaneous,   344 

insensible  and  sensible,  344 

ordinary  constituents  of,  345 
Peyer's  glands,  241 

functions  of,  243 

patches,  241 

resemblance  to  vascular  glands, 
245,  326 

structure  of,  243 

Pharynx,  action  of  in  swallowing,  213, 
396,  440 

influence     of    glosso-pharyngeal 

nerve  on,  428 
of  pneumogastric   nerve   on, 

439,  440 
Phosphates  in  tissues,  25 

present  in  albumen,  22 
in  blood,  73,  75 
in  urine,  366 
Phosphorus  in  human  body,  25 

union  of  with  oxygen  producing 
heat,  193,  note. 

in  urine,  source  of,  366 
Phrenology,  422 
Physiology,  definition  of,  13 
Pia  mater,  circulation  in,  151 
Pigment,  42 

of  choroid  coat  of  eye,  500 

composition  of,  43 

of  hair,  302,  340 

of  skin,  333 

uses  of,  43 

Pigment-cells,  form  of,  31,  42 
Pineal  gland,  424 
Pinna  of  ear,  527 

"  Pins  and  needles,"  sensation  of,  380 
Pitch  of  voice,  486 
Pith  of  hair,  340 
Pituitary  gland,  424 
Placenta,  587,  589 

formation  of,  591 

foetal  and  maternal,  593 


Placenta,  relation  of  to  the  liver,  263 

structures  composing,  593 
Plants,  distinctions  from  animals,  15 
Plexuses  of  nerves,  372 

terminal,  373 
of  spinal  nerves,  relation  to  cord, 

390 

Pneumogastric  nerve,  438 
distribution  of,  438 
mixed  function  of,  438 
influence  on  action  of  heart,  113 
on  deglutition,  214 
on  digestion,  235 
on  functions  of  larynx,  438, 

439 

of  oesophagus,  440 
of  lungs,  440 
of  pharynx,  439 
on   movements   of   stomach, 

236 

on  respiration,  406,  441 
on  secretion  of  gastric  fluid, 

236 
on  sensation  of  hunger,  234 

of  thirst,  234,  235 
origin  of  from  medulla  oblongata, 

406 
Poisoned    wounds,    absorption    from, 

298 

Poisons,  narcotic,  introduced  in  stom- 
ach, 235 

Polarity  of  muscles,  467,  note. 
Polygamous  birds,  their  cerebella,  417 
Pons  Varolii,  its  structure,  409 
Portal  blood,  characters  of,  79 
canals,  254 
circulation,  90 

function  of  spleen   with    re- 
gard to,  332 

veins,  arrangement  of,  254 
Portio  dura,  of  seventh  nerve,  433 

mollis,  of  seventh  nerve,  533 
Post-mortem     rigidity.       See     Rigor 

Mortis. 

Posture,  effect  of  on  the  heart's   ac- 
tion, 109 

Potassium,  salts  of,  in  fluids  and  tis- 
sues, 25 
Pregnancy,  absence  of    menstruation 

during,  569 
corpus  luteum  of,  572 
influence  on  blood,  76 
Presbyopia,  or  long-sightedness,  512 
Pressure  on  eye,  effects  of,  522 
Primary  membrane,  314,  318 
Primitive  dental  groove,  53 

fasciculi    and   fibrils  of    muscle, 

458,  459 

groove  in  embryo,  581 
Principles,  nitrogenous,  21 
non-nitrogenous,  20 


INDEX. 


647 


Process,  vermiform,  414 
Processus  gracilis,  529 

a  cerebello  ad  testes,  419 
Prostate  gland,  573 

functions  of  secretion  unknown, 

577 

Protagon,  69 
Proteids,   199 
Protein-compounds,  22 
Protoplasm,  27,  71 
Ptyalin,  action  of,  212 
Puberty,  changes  at  period  of,  567 
indicated  by  menstruation,  569 
Pudenda,  563 

Pulmonary  artery,  valves  of,  94,  105 
capillaries,   159 
circulation,  89 

influence  of  carbonic  acid  on, 

187 
of  pneumogastric   nerve 

on,  44J 

velocity  of.  149 
Pulp  of  hair,  302 

of  teeth,  51 
Pulse,  arterial,  123 
cause  of,  123 
dicrotous,  129 
difference  of  time  in,  124 
explanation  of,  126 
frequency  of,  108 
influence  of  age  in,  109 

of  food,  posture,  &c.,  109 
observations   on    with    sphygmo- 

graph,  124-126 
relation  of  to  respiration,  110 
tracings  of,  126,  129 

in  large  arteries,  128 
in  radial  artery,  128 
variations  in,  109,  110 
in  capillaries,  135,  136 
Pupil  of  eye,  office  of,  506 

relation  of  third  nerve  to,  426 
Purgative  action  of  bile,  262,  263 
Pus,  contains  albumen,  22 
Putrefaction.     See  Decomposition. 

arrested  by  gastric  fluid,  221 
Pylorus,  structure  of,  215 

action  of,  231,  232 
Pyramidal  portion  of  kidney,  350 
Pyramids  of  medulla  oblongata,  404, 
405 


Quadrupeds,  retinae  of,  523 


Radiation  of  impressions,  385,  395 
Rectum,  248 

evacuation  of,  a  reflex  act,  399 

mechanism  of,  234 
Reflexion  of  impressions,  285 


Reflexion  by  medulla  oblongata,  406 

by  spinal  cord,  395 
Reflex  actions,  385,  399 
in  accidents,  400 
conditions  necessary  to,  386 
in  disease^  400 
examples  of,  396,  399 
excito-motor   and  sensori-motor, 

398,  note. 

general  rules  of,  385 
independent  of  mind,    386,   396- 

399 

influence  of  cord  on,  396,  400 
irregular  in  disease,  386 

after  separation  of  cord  from 

brain,  396-399 
purposive  in  health,  386 
relation  of  fifth  nerve  to,  430 
relation  to  volition,  399 

to    walking,     running,     Ac., 

400 

sustained,  386 
in  tetanus,  Ac.,  401 
Reflex  functions  of  medulla  oblongata, 

406 

of  spinal  cord,  396 
Refraction,  laws  of,  505 
Refracting  media  of  eye,  505 
Renal  arteries,  arrangement  of,  352 

veins,  blood  of,  80 
Repair.     See  Nutrition. 

retarded  in  paralyzed  parts,  308 
Repetition,  nutritive,  305 
Reproduction,  nutritive,  305 
Reserve  air,  167 
Residual  air,  167 
Respiration,  155 

abdominal  type  of,  163 
ammonia  and  other  products  ex- 
haled by,  179 

carbonic  acid  increased  by,  173 
changes  of  air  in,  173 

of  blood  in,  179 
costal  types  of,  163 
force  of,  168-171 
frequency  of,  168 
influence  of  brain  on,  398 

of  medulla   oblongata,    185- 

186,  405-408 
of  pneumogastric  nerve,  406, 

440 

mechanism  of,  161 
movements  of,  162.     See  Respira- 
tory Movements. 
of  air  in,  171 
of  blood  in,  172 
nitrogen  in  relation  to,  177 
oxygen  diminished  by,  177 
quantity  of  air  changed  in,  166 
relation  of  to  the  pulse,  110 
structure  of  organs  of,  156-161 


648 


INDEX. 


Respiration,  suspension  and  arrest  of, 

186 
temperature  of  air  increased  by, 

173 

types  of,  163 

watery  vapor  exhaled  in,  177 
Respiratory  capacity  of  chest,  167 
function  of  skin,  346 
movements,  162-166 
of  air-tubes,  171 
centre  of  the  medulla  oblon- 

gata,  406 

effect  of  on  circulation,  145 
excited  through  nerves,  406 
by  various  stimuli,  407 
of  expiration,  164 
of  glottis,  166 

influence  on  amount  of  car- 
bonic acid,  174 
of  inspiration,  162 
relation  to  will,  398 
various,  mechanism  of,  166 
muscles,  162,  165 
power  of,  169 
secondary,  186 
nerves,  186 
rhythm,  165 

tract  of  mucous  membrane,  317 
Rest,  favorable  to  coagulatioji,  62 
Restiform  bodies,  403,  404 
Retching,  explanation  of,  233 
Rete  mucosum,  333 

testis,  573 

Retiform  tissue,  216,  239,  285 
Retina,  501 

duration  of  impressions  on,  517 

of  after-sensations,  517 
effect  of  pressure  on,  522 
focal  distance  of,  510 
function  of,  504 
image  on,  how  formed  distinctly. 

508 
inversion  of,  how  corrected, 

513 
insensible    at   entrance    of  optic 

nerve,  520 
insufficient     alone     for     distinct 

vision,  505 
in  quadrupeds,  523 
reciprocal  action  of  parts  of,  519 
in  relation  to  direction  of  vision, 

515 

to  motion  of  bodies,  516 
to  single  vision,  521 
to  size  of  field  of  vision,  513 
structure  of,  501 
Rhythm  of  heart,  cause  of,  111.     See 

Heart. 

respiratory,  165 
Rigor  mortis,  465 

affects  all  classes  of  muscles,  466 


Rigor  mortis,  phenomena  and  causes 

of,  465 

Rima  glottidis,  movements  of  in   res- 
piration, 166 
RodsofCorti,  532 

use  of,  543 
Root  of  nail,  341 
Root-sheath  of  hair,  341 
Roots  of  spinal  nerves,  388,  390 

anterior    and    posterior,    special 

properties  of,  391 
Rotation,   following    injury  of  crura 

cerebelli,  418 
produced  by  dividing   the  crura 

cerebri,  4  1 1 
Rouleaux,  formation  of  in  blood,  60, 

68 

Rubbing,  influence  on  cutaneous  ab- 
sorption, 347 

Rugae  or  folds  of  stomach,  215 
Rumination,  233 
Running,  mechanism  of,  473 
Rut  or  heat,  568 


Saccharine  principles  of  food,   diges- 
tion of,  230 

action  of  bile  on,  266 

absorption  of,  271 
Sacculus,  533 
Safety-valve  action  of  tricuspid  valve, 

101 

Saline  constituents  of  bile.  260 
Saline  constituents  of  blood,  75 

use  of,  86 
of  urine,  288 

matters,  absorption  of,  295 
Saliva,  action  of  on  food,  212 
on  starch,  213 

composition  of,  210 

digestive  properties  of,  212 

mechanical  purposes  of,  211 

organs  for  production  of,  209 

physical  properties  of,  210 

purposes  of,  211 

quantity  secreted,  211 

rate  of  secretion,  210 

reaction  of,  210 

relation  to  gastric  fluid,  212 
Salivary  glands,  209 

development  of,  607 
Salts,  alkaline  and  earthy,   influence 

on  coagulation,  62 
Sarcode,  27 
Sarcolernma,  458 
Sarcous  elements,  459 
Scala  media,  532 

tympani,  532 

vestibuli,  532 
Sclerotic,  500,  507 
Scurvy  from  want  of  vegetables,  207 


INDEX. 


649 


Season,  influence  on  carbonic  acid  ex- 
pired, 1 75 
Sebaceous  glands,  339 

their  secretion,  344 
Secreting  glands,  319 
aggregated,  319 
convoluted  tubular,  321 
tubular  or  simple,  319 
Secreting    membranes.     See   Mucous 

and  Serous  Membranes. 
Secretion,  313 

action  of  cells  snd  nuclei  in,  322 
apparatus  necessary  for,  314 
circumstances  influencing,  324 
discharge  of,  323 
general  nature  of,  313 
influence  of  nervous  system  on, 

324 

of  sj'inpathetic  nerve,  450 
of  quantity  of  blood,  324 
process  of,  313 

relation  or  antagonism  of,  325 
resemblance  to  nutrition,  322 
by  membrance,  314 
mucous,  316 
serous,  315 
synovia!,  316 
in  vascular  glands,  324 
Selection  of  materials  for  absorption, 

290 

Semicircular  canals  of  ear,  530 
development  of,  606 
use  of,  54 1 
Semilunar  valves,  96 

action  of,  102 
Seminal  fluid,  574 

composition  of,  577 
corpuscles    and   granules  of, 

574 

emission  of,  a  reflex  act,  599 
influence  on  ovum  and  em- 
bryo, 578 
filaments,  574 

purpose  of,  574 
tubes,  573 
vesicles,  576 

Sensation  attended  by  ideas,  558 
cerebral  nerves  of,  524 
common,  489 

conditions  necessary  to,  558 
conduction  of  in  spinal  cord,  393 
contrasts  in,  558 
definition  of,  489 
excited  by  mind,  559 

by  internal  causes,  491 
of  hunger,  234 

influence  of  attention  on,  494,  516 
influence    of  mind   necessary  to, 

558 

of  motion,  how  perceived,  492 
muscular,  461,  557,  558 


Sensation  of  necessity  of  breathing, 

235 
nerves  of,  377 

convey  impressions  to  centres 

only,  379 
impressions   on    referred    to 

periphery,  380,  381 
laws  of  action  of,  386 
perceived  in  cerebrum,  419,  420 
preservation    of     in      paralyzed 

nerves,  382 

referred  to  exterior,  382 
special,  489 
stimuli  of,  377,  378 

of  special,  490-492 
in  stumps,  381 
subjective,  558 
of  thirst,  234 
sympathetic,  385 
touch  a  modification  of,  554 
transference    and    radiation     of, 

385,  395 

two  kinds  of,  489 
of  volatile  bodies,  493 
of  weight,  557 
Sense,  of  hearing,  527.     (See  Hearing, 

Sound. 

of  sight,  499.     (See  Vision, 
of  smell,  494.     See  Smell, 
of  taste,  547.     See  Taste, 
of  touch.     See  Touch, 
muscular,  416,  557,  558 
special,  nerves  of,  424 
organs  of,  development  of,  603 
Senses,  special,  general  properties  of, 

489 
action  of    external   and   internal 

stimuli  on,  491 
impairment  of   from    division   of 

the  facial  nerve,  434 
from  division  of  the  fifth  nerve, 

431 
influence  of  attention  on,  494 

of    internal    impressions    on 

nerves  of,  491 

qualities  of  external  matter  per- 
ceived by,  490,  492 
special  nerves  of,  490 
stimulus  excites  in  each  nerve  its 

own  sensation,  490 
Sensitive  impressions,  conduction  of, 

380 

by  spinal  cord,  392,  393 
reference  of,  380-382 
nerves,  378 
Sensory  ganglia,  413 
Septum    between   auricles,  formation 

of,  600 
between  ventricles,  formation  of, 

600 
Serosity  of  blood,  73 


650 


INDEX. 


Serous   layer    of  blastodermic    mem-  j 

brane,  581,  582 
Serous  membranes,  315 
arrangement  of,  315 
communication      of     lymphatics 

with,  280,  282 
epithelium  of,  315 
fluid  secreted  by,  316 
lining  joints,  &c.,  315 

visceral  cavities,  315 
purpose  of,  315 
stomata,  282 
structure  of.  315 
Serum,  of  blood,  72 

chief  source  of  albumen,  22 
separation  of,  58,  72 
Seventh  cerebral  nerve,  auditory  por- 
tion, 533,  543 
facial  portion,  433 
Sex,  influence  on  blood,  76 

influence  on    production  of  car- 
bonic acid,  174 
relation  of  to  capacity  of    chest, 

168 

to  respiratory  movements,  163 
Sexual  organs  and  functions   in   the 

female,  560,  572 
in  the  male,  573,  578 
Sexual    passion,   connection  of    with 

cerebellum,  417 
Sighing,  mechanism  of,  181 
Sight.      See  Vision. 
Silica,  parts  in  which  found,  25 
Singing,  mechanism  of,  483 
Single  vision,  conditions  of,  421 
Sinus  terminalis,  588 
urogenitalis,  610 
Sinuses  of  dura  mater,  151 
Sixth  cerebral  nerve,  426 
Size  of  field  of  vision,  436-438 
Skin,  332 

absorption  by,  347 
of  gases,  348 

of  metallic  substances,  347 
of  water,  347 
capillaries  of,  136 
cutis  vera  of,  334 
epidermis  of,  333 
evaporation  from,  349 
excretion  by,  344-348 
exhalation  of  carbonic  acid  from, 

346 

of  watery  vapor  from,  345 
functions  of,  332 

respiratory.  346 
papilla  of,  336-338 
perspiration  of,  344 
rete  mucosum  of,  333 
sebaceous  glands  of,  339 
structure  of,  333 
sudoriparous  glands  of,  338 


Sleep,  influence  of  on    production   of 

carbonic  acid,  177 
Smell,  sense  of,  494 
conditions  of,  494 
different  kinds  of  odors,  498 
impaired  by  leeion  of  facial  nerve, 

434 
impaired  by  lesion  of  fifth  nerve, 

431 

internal  excitants  of,  498 
limited  to  olfactory  region,  496 
relation   to   common    sensibility, 

496 

structure  of  organ  of,  495 
subjective  sensations  of,  498 
varies  in  different  animals,  498 
Sneezing,  caused  by  sun's  light,  384 

mechanism  of,  182 
Sniffing,  mechanism  of,  184 

smell  aided  by,  495 
Soda,  salts  of  in  blood,  74 
in  solids  and  fluids,  25 
Sodium  in  human  body,  25 

chloride  of,  in  albumen,  22 
Solid  food,  action  of  gastric  fluid  on, 

222 

Solitary  glands,  241 
Sonorous    vibrations,  how    communi- 
cated in  ear,  536,  e.  s. 
in  air  and  water,  537.    Se-e  Sound. 
Soprano  voice,  483 
Sound,  conduction  of  by  ear,  533 
by  external  ear,  534-536 
by  internal  ear,  540-543 
by  middle  ear,  536-541 
movements   and   sensations   pro- 
duced by,  546 
perception  of,  543 

of  direction  of,  544 
of  distance  of,  544 
a  state  of  the  auditory  nerve, 

545 

permanence  of  sensation  of,  545 
produced  by  contraction  of  mus- 
cle, 463 

production  of,  543 
subjective,  546 

Sounds  as  expressions  of  passion,  483 
classified,  483 
of  heart,  105 

causes  of,  106 

Sources  of  nervous  force,  383 
Spasms,  reflex  acts,  400 
Speaking,  483 

mechanism  of,  184 
Special  sense.     See  Senses. 
Spectrum  analysis,   78 

of  blood,  78 
ocular,  517-519 
Speech,  486 

function  of  tongue  in,  489 


INDEX. 


651 


Speech,  influence  of  medulla  oblongata 

on.  408 

Sperinatozoids,  development  of,  574 
form  and  structure  of,  574 
function  of,  574 
motion  of,  574 
Spherical   aberration,  how  corrected 

in  the  eye,  509 
Spheroidal  epithelium,  35 
Sphincter  ani,  external,  276 
internal,  249,  276 
influence  of  soinal  cord  on,  396, 

401 

Sphygmograph,  124 
Spinal  accessory  nerve,  443.     See  Ac- 
cessory Nerve. 
Spinal  cord,  386 
canal  of,  388 
a  collection  of  nervous   centres, 

401 

columns  of,  391 
commissure  of,  391 
conduction    of    impressions    by, 

392-395 

course  of  fibres  in,  389 
decussation   of  sensitive   impres- 
sions in.  394 
effect  of  injuries  of,  on  conduction 

of  impressions.  393 
on  nutrition,  308-310 
enlargement  of  parts  of,  390 
fissures  and  furrows  of,  388 
functions  of,  393-402 

of  columns,  392 

influence  of  on  heart's  actions,  112 
on    lymph-hearts,    293, 

401 
on    sphincter    ani,    396, 

401 

on  tone,  402 

morbid  irritability  of,  401 
nerves  of,  390-392 
reflex  function  of,  395.     See  Re- 
flex Action, 
size  of  parts  of,  390 
structure  of,  388  . 
transference   and    radiation    in, 

384,  395 
Spinal  nerves,  origin  of,  390 

physiology  of,  443 
Spiral  canal  of  cochlea,  531 
lamina  of  cochlea,  532 

function  of,  542 

Spleen,  as  a  blood-forming  organ,  331 
in  relation  to  digestion,  332 

to  portal  circulation,  332 
hilus  of,  327,  328 
Mulpighian  corpuscles  of,  328 
pulp,  328 
structure  of,  327 
trabeculae  of,  327 


Spleen,  stroma  of,  327 
Splenic  vein,  blood  of.  79 
Spontaneous  decomposition,  19 
Spot,  germinal,  565 
Squamous  epithelium,  34 
Stapediu-s  muscle,  529 

function  of,  540 
Stapes,  529,  530 
Starch,  action  of  cooking  on,  230 

of  pancreatic  secretion,  251 
of  saliva,  212 
of  various  substances,  212 
animal,  267 
digestion  of   in  small   intestine, 

271 

in  stomach,  230 
Starvation,  203 

loss  of  weight  in,  203 
effect  on  temperature,  204 
symptoms,  204 
period  of  death  in,  204 
appearances  after  death,  204  f 

Statical  pressure  of  blood.  129 
Stature,  relation  to  capacity  of  chest, 

167 

Stearin,  20 

Sellate  nerve-corpuscles,  375 
Stercorin,  274 

allied  to  cholesterin,  260 
Stereoscope,  526 
Still  layer  in  capillaries,  137 
Stimuli,  as  excitants  of  contractility, 

463-465 

of  sensation,  377,  379 
of  special  senses,  491,  492 
St.  Martin,  Alexis,  case  of,  220,  223, 

227 

Stomach,  bloodvessels  of,  219 
development  of,  607 
digestion  in,  225-230 

influence  of  nervous  system 

on,  234 

digestion  of  after  death,  236 
examined   through   fistulse,    220, 

226 
glands  of,  216 

lenticular,  219 
tubular,  216 
movements  of,  231 

influence  of  nervous  system 

on,  236 

in  vomiting,  232 
mucous  membrane  of,  215 
muscular  coat  of,  215 
passage    of    substances   from    to 

urine.  354 

presence    of   not  absolutely  dis- 
tinctive of  animals,  17 
in  relation  to  hunger,  234 
secretion    of,    219.     See    Gastric 
Fluid. 


652 


INDEX. 


Stomach,  structure  of,  214 

temperature  of,  220 
Striped  muscular  fibre,  458-460 
Stroma  of  ovary,  561 
Structural   changes  of  food   in   stom- 
ach, 228 
Structural     composition     of     human 

body,  26 

Stumps,  sensations  in,  381 
Subjective  sensations,  558 
of  sound,  546 
of  taste,  554 
Sublobular  veins,  255 
Sucking,  mechanism  of,  184 
Sudoriparous  glands/  338 
their  distribution,  339 
number  of,  339 
their  secretion,  344 
Suflbcation,  186-189 
Sugar,  digestion  of,  230,  266 

as  food,  experiments  with,  201 
formation  of  in  liver,  267-272 
Sulphates  in  urine,  365 
Sulphur,  in  bile,  261 
in  human  body,  25 
union  of  with  oxygen  producing 

heat,  177,  193,  note. 
in  urine,  365 

Suprarenal  capsules,  326,  327 
development  of,  609 
disease  of,  relation  to  discolora 

tion  of  skin,  330,  note. 
Swallowing,  213 
Sweat,  344 
Sympathetic  nerve,  445 

character  of  movements  executed 

through,  451 
communication     of     with     fifth 

nerve,  432,  445 
with  glosso-pharyngeal  nerve, 

445 
with    pneumogastric    nerve, 

439,  445 

with  sixth  nerve,  426 
with  spinal  nerves,  445 
conduction  of  impressions  by,  450 
divisions  of,  445 
fibres  of,  course  of,  447 

differences   of  from   cerebro- 

spinal  fibres,  371,  445 
mixture  with   cerebro-spinal 

fibres,  448 

relation  to  cerebro-spinal  sys- 
tem, 453 
ganglia  of,  445 
action  of,  451 
co-ordination  of  movements 

by,  451 

in  substance  of  organs,  451 
influence  of  on  bloodvessels,  122, 
453 


Sympathetic   nerve,    influence   of  on 

heart's  action,  111 
on  involuntary  motion,  450 
on  nutrition,  386,  452 
on  secretion.  324,  452 
physiology  of,  447-453 
structure  of,  445-447 
Synovial  fluid,  secretion  of,  316 

membranes,  315 
Syntonin,  23 

Systemic  circulation,  89.     See  Circu- 
lation. 
vessels,  91 


Tact,  489.     Sett  Touch. 
Tannic  acid,  test  for  gelatin,  21 
Tanno-gelatin,  21 
Taste,  547 

conditions  for  perception  of,  547 

connection  with  smell,  553 

impaired  by  injury  of  facial  nerve, 

434 
of  fifth  nerve,  431 

nerves   on    which   the   sense  de- 
pends, 437,  552,  553 

permanence  of  impressions,  553 

seat  of,  548 

subjective  sensations,  554 

variations  of,  553 
Taurin,  sulphur  combined  with,  261, 

note. 

Taurocholic  acid,  259 
Teeth,  51 

development   and   casting  of,  53, 
303 

parts  of,  51 

structure  of,  51 

temporary  and  permanent,  54 
Temperament,  influence  on  blood,  76 
Temperature,  average  of  body,  189 

changes  of,  effects  of,  191 

circumstances  modifying,  189 

of  cold-blooded  and  warm-blooded 
animals,  192 

in  diseases,*  191 

increased  power  of  supporting,  196 

influence  on  amount  of  carbonic 
acid  produced,  175 

on  nerves,  378 

loss  of,  194 

maintenance  of)  192,  193 

of  Mammalia,  birds,  Ac.,  191 

modified  by  age,  &c.,  189 

of  paralyzed  parts,  198 

regulation  of,  194 

relation  of  to  combustion  of  car- 
bon and  hydrogen,  192 

of  respired  air,  173 

sensation   of  variations  of,    558. 
See  Heat. 


INDEX. 


653 


Temporary  cartilage,  43,  44 

teeth,  54 

Tendinous  cords,  94 
Tendons,  structure  of,  40 
Tenor  voice,  483 
Tensor  tympani  muscle,  529 

office  of,  540 

Tessellated  epithelium,  34 
Testicle,  573 

development  of,  609 

structure  of,  573 

Tetanus,  reflex  movements  in,  401 
Thalami  optici,  function  of,  411 
Third  cerebral  nerve,  425 
Thirst,  allayed  by  cutaneous  absorp- 
tion, 348 

cause  of,  77 

sensation  of,  234 
Thoracic  duct,  279 

its  contents,  289 
Thorax,  88 
Thymus  gland,  327 

function  of,  328 
Tbyro-arytenoid  muscles,  481 
Thyroid  gland,  326 

function  of,  330 

Thyroid  cartilage,  structure  and  con- 
nections of,  478 
Timbre  of  voice,  484 
Tissue,  adipose,  40 

areolar,    cellular,    or  connective, 
38 

fatty,  40 

muscular,  456 
Tissues,  absorption  of,  292 

elementary,  structure  of,  34 

decay  and  removal  of,  300 

erectile,  152 

mutually  excretory,  85 

nitrogenous,    urea  derived  from, 
361 

nutrition  of.     See  Nutrition. 

relation  to  blood,  140 

vascular  and  non-vascular,  307 
Tone  of  bloodvessels,  122 

of  muscles,  402 

of  voice,  483 
Tongue,  548 

action  of  in  deglutition,  214 
in  sucking,  184 

epithelium  of,  521 

function  of  in  speech,  489 

influence  of  facial  nerve  on  mus- 
cles of,  434 

motor  nerve  of,  444 

an  organ  of  touch,  552 

papillae  of,  548 

parts  most  sensitive  to  taste,  552 

structure  of,  548 

Toothache,  radiation  of  sensation  in, 
385 


Tooth-fang,  51 

absorption  of,  303 
Tooth-pulp,  51,  52,  54 
Touch,  554 

after-sensation  of,  558 

characters  of  external  bodies  as- 
certained by,  555 

conditions  for  perfection  of,  556 

connection     of     with     muscular 
sense,  557 

co-operation  of  mind  with,  558 

function  of  cuticle  with  regard  to, 
338 

of  papillae  of  skin  with  regard  to, 
337 

the  hand  an  organ  of,  555 

modifications  of,  556 

a  modification  of  common  sensa- 
tion, 489,  554 

special  organs  of,  555 

subjective  sensations  of,  558 

the  tongue  .an  organ  of,  552 
Touch-corpuscles,  336,  373 
Trachea,  88 

structure  of,  157 
Tracts  of  medulla  oblongata,  402 

of  mucous  membrane,  317 

of  spinal  cord,  388 
i  Tradescantia    Virginica,     movements 

in  cells  of,  27 
!  Tragws,  527 

|  Transference  of  impressions,  384,  395 
Transplanted  skin,  sensation  in,  381 
Tricuspid  valve,  92 

safety-valve  action  of,  101 
Trigerninal  or  fifth  nerve,  428 

effects  of  injury  of,  309,  430 
Trochlearis  nerve,  426 
Trophic  nerves,  310,  377 
Tube,  Eustachian,  540 
Tubes,  Fallopian.  See  Fallopian  Tubes. 

looped,  of  Henle,  351 
[  Tubular  glands,  319 

convoluted,  321 

simple,  319 

of  intestines,  249 

of  stomach,  217 

Tubules,  general  structure  of,  33 
Tubuli  setniniferi,  573 

uriniferi,  350 

Tunica  albuginea  of  testicle,  573 
Tympanum  or  middle  ear,  527 

development  of,  605 

functions  of,  536 

membrane  of,  527 

structure  of,  528 

use  of  air  in,  538 
Types  of  respiration,  164 


Ulceration  of  parts  attending  injuries 
of  nerves,  308,  431,  432 


55 


654 


INDEX. 


Ulnar  nerve,  effects  of  compression  of, 

379 

of  division  of,  382 
Umbilical  arteries,  contraction  of,  119 

vesicle,  582 

Understanding,    relation    of   to    cere- 
brum, 420 

Unstriped  muscular  fibre,  456 
Urachus.  587 
Urate  of  ammonia,  363 

of  soda,  362,  363 
Urea,  359 

in  blood,  76,  361 

chemical  composition  of,  360 

identical    with    cyanate   of   am- 
monia, o60 

properties  of,  360 

quantity  of,  360 

in  relation  to  muscular- exertion, 
361,  474 

sources  of,  361 
Ureter,  350 

arrangement  of,  355 
Urethra,  development  of,  613 
Uric  acid,  362 

in  blood.  76 

condition    in    which    it  exists  in 
urine,  362 

forms   in  which    it   is  deposited, 
363 

proportionate  quantity  of,  362 

source  of,  363 

Urina  sanguinis,  pottis,  et  cibi,  357 
Urinary  bladder,  action  of,  355 

development  of,  610 

evacuation  of,  a  reflex  act,  399 

hypertrophy  of,  312 

regurgitation  from  prevented,  355 
Urine,  354-367 

analyses  of,  358 

animal  extractive  in,  364 

chemical  composition  of,  357 

chlorine  in,  366 

color  of,  356 

coloring  matter  of,  364 

creatin  and  oreatinin  in,  364 

cystin  -in,  367 

decomposition  of  by  mucus,  364 

expulsion  of,  356 

flow  of  into  bladder,  355 

gases  in,  367 

general  properties  of,  356 

hippuric  acid  in,  363 

mucus  in,  364 

oxalic  acid  in,  367 

phosphorus  in,  365 

quantity  secreted,  357 

reaction  of,  356 

made  alkaline  by  diet,  356 

saline  matters  in,  365 

secretion  of,  354 


Urine,  secretion  of,  effects  of  posture, 

&c.,  on,  355 
rate  of,  355 
specific  gravity  of,  356 
sulphur  in,  365 
urea  in,  359 
uric  acid  in,  362 
variations  of,  356 

of  water  in,  359 
Uterus,  562 

changes  of  mucous  membrane  of, 

591 
contractions  of  its  arteries,  119, 

120 

development  of  in  pregnancy,  312 
follicular  glands  of,  589 
reflex  action  of,  400 
simple  and  compound  glands  of, 

589 

structure  of,  562 
Utriculus  of  labyrinth,  533 
Uvula  in  relation  to  voice,  486 


Vagina,  structure  of,  562 
Vaginal  veins  of  liver,  255 
Vagus  nerve.     See  Pneumogastric. 
Valve,  ileo-caecal,  structure  of.  250 

of  Vieussens,  419 
Valves  of  heart,  92 

action  of,  99-105 

bicuspid  or  mitral,  92 

semilunar,  96 

tricuspid,  92 

of  lymphatic  vessels,  282 

of  veins,  142 
Valvulae  conniventes.  240 
Vas  deferens,  573 
Vasa  efferentia,  354,  573 

recta,  354,  573 

vasorum,  115 
Vascular  area,  588 
Vascular  glands,  325 

analogous   to    secreting    glands, 
326 

in  relation  to  blood,  329 

several  offices  of,  330-332 
Vascular  parts,  nutrition  of,  307 

system  development  of,  597 
Vaso-motor  nerves,  121,  452 
Vaso-motor  nerve-centre,  452 

reflection  by,  453 
Vascularity,  degrees  of,  134 
Vegetable  matters,  absorption  of,  347 
Vegetable    substances,    digestion    of, 

228 
Vegetables  and  animals,  distinctions 

between,  15 
Veins,  88,  141 

absorption  by,  293 

anastomoses  of,  144 


INDEX. 


655 


Veins,  circulation  in,  142 
coats  of,  141 
of  cranium,  151 
effects  of  muscular  pressure  on, 

143 

of  respiration  on,  146 
in  erectile  tissues,  152 
foice  of  heart's  action  remaining 

in,  143 

influence  of  gravitation  in,  142 
muscular  pressure  in,  144,  145 
rhythmical  action  in,  145 
structure  of,  141 
systemic,  92 
valves  of,  142 
velocity  of  blood  in.  147 
Velocity  of  blood  in  arteries,  147 
in  capillaries,  137 
in  veins,  147 
of  circulation,  147 
of  nervous  force,  379 
Vena  portae,  its  arrangement,  89,  90, 

254 

Venous  blood,  characters  of,  77-80 
Ventilation,  necessity  of,  176 
Ventricle,  fourth,  of  brain,  404,  419 
Ventricles  of  heart,  91 
capacity  of,  111 
contraction  of,  98 

effect    on    arteries, 

123,  127 

on  circulation,  114 
on  veins,  143 
force  of,  110 
development  of,  599 
dilatation  of,  99 
of  larynx,  office  of,  486 
Ventriloquism,  544 

mechanism  of,  544 
Vermicular   movement  of  intestines, 

276 

Vermiform  process,  414 
Vertebrae,  development  of,  582,  594 
Vesicle,  germinal,   565 
Graafian,  561,  563 

bursting  of,  567-568 
umbilical,  582 

Vesicles  of  vascular  glands,  326 
Vesicula  germinativa,  565 
Vesiculae  seminales.  576 
functions  of,  576 
reflex  movements  of,  399 
Vesicular  nervous  substance,  375 
Vestibule  of  the  ear,  530 

of  vagina,  562 
Vibrations,  conveyance  of  to  auditory 

nerve.  536 
perception  of,  492 
of  vocal  cords,  485 
Vidian  nerve,  433 
Villi  of  intestines,  246 


Villi  of  intestines,  action  in  digestion, 

270 

on  intestinal  glands,  241 
Villi  of  chorion,  588 
in  placenta,  592 

Visceral  arches,  development  of,  596 
cavities,    serous    membranes    of, 

315 

laminae,  582,  595 
layer  of  pleura,  157,  note. 
Vision,  499 

angle  of,  514 

at  diiferent  distances,  adaptation 

of  eye  to,  510,  511 
contrasted  with  touch,  515 
corpora  quadrigemina  the  princi- 
pal nerve-centres  of,  411 
correction  of  aberration,  509,  510 

of  inversion,  513 
direction  of,  515 

direction   of  rays   in,   how  regu- 
lated, 505 

distinctness  of,  how  secured,  508 
double,  523 

duration  of  sensation  in,  517 
estimation  of  the  form  of  objects, 

515 

of  their  motion,  516 
of  their  size,  513 
field  of,  size  of,  513 
focal  distance  of,  510 
impaired  by  lesion  of  fifth  nerve, 

430,  431 

influence  of  attention  on,  516 
modified  by  different  parts  of  the 

retina,  519 

organ  of,  499.     See  Eye. 
phenomena  of,  506 
in  quadrupeds,  523 
single,  with  two  eyes,  521 

its  cause,  524-526 
structures  essential  for,  507 
Visual  direction,  515 
Vital  capacity  of  chest,  167 

motions,  454 
Vitality.     See  Life. 
Vitelline  duct,  584 

membrane.  564,  579 
spheres,  579   . 

Vitellus,  or  yelk,  564.     See  Yelk. 
Vitreous  humor,  506 
Vocal  cords,  action  of  in  respiration, 

166,  182 
approximation  of,  effect  on  height 

of  note,  481 
attachment  of,  478 
elastic  tissue  in,  40 
longer  in  males  than  in  females, 

484 

position  of,  how  modified,  481 
vibrations  of,  cause  voice,  475,  485 


656 


INDEX. 


Voice,  474 

of  boys,  484 
compass  of,  483 

conditions  on  which  strength  de- 
pends, 485 
human,  produced  by  vibration  of 

vocal  cords,  474,  485 
impaired  by  destruction  of  acces- 
sory nerve,  443 
in  eunuchs,  484 
influence  of  age  on,  484 

of  arches  of  palate  and  uvula, 

486 

of  epiglottis,  481 
of  sex,  483 

of  ventricles  of  larynx,  486 
of  vocal  cords,  476,  481 
in  male  and  female,  483 

cause  of  different  pitch,  484 
modulations  of,  485 
natural  and  falsetto,  485 
peculiar  characters  of,  484 
varieties  of,  483 
Volatile  bodies,  influence  of  on  sense 

of  smell,  496,  497 
Voluntary  muscles.     See  Muscles. 
Vomiting,  action  of  stomach  in,  232 
mechanism  of,  183 
influence  of  spinal  cord  in,  399 
voluntary  and  acquired,  233 
Vowels  and  consonants,  487 
Vulvo-vaginal  glands,  563 


Walking,  muscular  action  in,  469,  472 
Warm-blooded  animals,  192 
Water,  absorbed  by  skin,  347 

by  stomach,  226 
in  blood,  variations  in,  73 
conduction  of  sound  through,  537 


Water  deficient  in  thirst,  77 

exhaled  from  lungs,  178,  346 

from  skin,  344 
forms  large  part  of  human  body, 

25 

influence    of   on    coagulation    of 
blood,  63 

on  decomposition,  20 
in  urine,  excretion  of,  354 

variations  in,  359 
vapor  of  in  atmosphere,  1 73 
Wave  of  blood  in  the  pulse,  127 
Weight,  relation  to  capacity  of  chest, 

167 

sensation  of,  557 

White  corpuscles.  See  Blood-corpus- 
cles, White  ;  and  Lymph-cor- 
puscles. 

fibro-cartilage,  43-45 
White  substance  of  nerve-fibre,  370 
Will,  reflex  actions  amenable  to,  398, 

399 

transmission  of  through  cord,  394 
Willis,  circle  of,  151 
Wolffian  bodies,  609 


Yelk,  or  viteilus,  564 

changes  of,  in  Fallopian  tube,  579 
in  uterus,  581 

cleaving  of,  579 

constriction  of  by  ventral  lamina, 

583 

Yelk-sac,  585 
Yellow  elastic  fibre,  40 

fibro-cartilage,  43,  45 

spot  of  Sommering,  501,  504 


Zona  pellucida,  564,  579 


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HEATH  (CHRTSTOPHEB).  PRACTICAL  ANATOMY  ;  A  MANUAL 
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CONSPECTUS  OF  THE  MEDICAL   SCIENCES.      Comprising 

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TTOBLYN  (RICHARD  D.)     A  DICTIONARY  OF  THE  TERMS  USED 
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HOLLAND  (SIR  HENRY).  MEDICAL  NOTES  AND  REFLECTIONS. 
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HILLIER  (THOMAF).  HAND-BOOK  OF  SKIN  DISEASES.  Second 
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TONER  (1.  HANDFIELD).     CLINICAL  OBSERVATIONS  ON  FUNC- 
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KIRKES  (WILLIAM  SENHOTJSE).  A  MANUAL  OF  PHYSIOLOGY. 
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KNAPP  (F.)  TECHNOLOGY  ;  OR  CHEMISTRY,  APPLIED  TO  THE 
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STUDIES  IN  CHURCH  HISTORY.     The  Rise  of  the  Temporal 

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AN  HISTORICAL   SKETCH   OF   SACERDOTAL  CELIBACY 

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T  ATTRENCE  (J.  Z.)   AND   MOON  (ROBERT  C.)     A  HANDY-BOOK 

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T  EHMANN  (C.  G.)     PHYSIOLOGICAL  CHEMISTRY.    Translated  by 
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T  AWSON  (GEORGE).   INJURIES  OF  THE  EYE,  ORBIT,  AND  EYE- 
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T  UDLOW  (J.  L.)     A  MANUAL  OF  EXAMINATIONS  UPON  ANA- 
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OBSTETRICS,  MATERIA  MEDICA,  CHEMISTRY,  PHARMACY, 

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MARSHALL  (JOHN).  OUTLINES  OF  PHYSIOLOGY,  HUMAN 
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WOMAN  :  HER  DISEASES  AND  THEIR  REMEDIES.     Fourth 

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-ON  THE  NATURE,  SIGNS,  AND  TREATMENT  OF  CHILD-BED 


FEVER      In  one  Svo.  vol.  of  365  pages,  extra  cloth,  $2. 

TV/TILLER  ( JAMES).    PRINCIPLES  OF  SURGERY     Fourth  American, 
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DRLAND  (W.  W.)  DISEASES  OF  THE  URINARY  ORGANS.  With 
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JRL<VND  (W.  W.)  ON  THE  RETENTION  IN  THE  BLOOD  OF  THE 
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AN  ATLAS  OF  CUTANEOUS  DISEASES.     In  one  handsome 

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•M-IEBUHR   (B.  G.)     LECTURES   ON    ANCIENT    HISTORY;    com- 
•*-*     prising     the     history    of    the     Asiatic     Nations,    the     Egyptians, 

Greeks,   Macedonians,   and  Carthagenians.     Translated  by  Dr.  L. 

Schmitz.     In  three  neat  volumes,  crown  octavo,  cloth,  $5  00. 

ODLING  (WILLIAM).  A  COURSE  OF  PRACTICAL  CHEMISTRY 
FOR  THE  USE  OF  MEDICAL  STUDENTS.  From  the  fourth 
revised  London  edition.  In  one  12mo.  vol.  of  261  pp.,  with  75  illus- 
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P.WY  (F.  W.)  A  TREATISE  ON  THE  FUNCTION  OF  DIGESTION  : 
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p  \RRISH  (EDWARD).     A  TREATISE  ON  PHARMACY.    With  many 
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vol.  of  850  pages,  with  several  hundred  illustrations,  extra  cloth,  $5  ; 

strongly  bound  in  leather,  $6. 

pIRRIE  (WILLIAM)      THE  PRINCIPLES  AND  PRACTICE  OF  SUR- 
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(JONATHAN).     MATERIA  MEDIC  A  AND  THERAPEU- 
-      TICS.     An  abridged  edition.     With  numerous  additions  and  refe- 
rences to  the  United  States  Pharmacopoeia.      By  Horatio  C.    Wood, 
M.  D.     In  one  large  octavo  volume,  of  1040  pages,  with  236  illustra- 
tions, extra  cloth  $7  00;  leather,  raised  bands,  $8  00. 

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PA.GET'8  HUNGARY  AND  TRANSYLVANIA.  In  two  royal  12mo. 
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ROBERTS  (WILLIAM).  A  PRACTICAL  TREATISE  ON  URINARY 
AND  RENAL  DISEASES.  A  second  American,  from  the  second 
London  edition.  With  numerous  illustrations  and  a  colored  plate. 
In  one  very  handsome  8vo.  vol.  of  616  pages.  (Now  ready.)  Extra 
cloth,  $4  50. 

RA.MSBOTHAM  (FRANCIS  H.)  THE  PRINCIPLES  AND  PRAC- 
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perial 8vo.  vol.  of  650  pages,  with  64  plates,  besides  numerous  wood- 
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RIGBY  (EDWARD).  A  SYSTEM  OF  MIDWIFERY.  Second  Ameri- 
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$2  50. 

•DANKE'S  HISTORY  OF  THE  TURKISH  AND  SPANISH  EMPIRES 
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—  HISTORY  OF  THE  REFORMATION  IN  GERMANY.     Parts  I. 
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EOYLE  (  J.  FORBES).  MATERIA  MEDIC  A  AND  THERAPEUTICS. 
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pages,  with  98  illustrations,  extra  cloth,  $3. 

EADCLIFFE,  AINSTIE,  AND  OTHERS,  ON  DISEASES  OF  THE 
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SMITH  (EUSTACE).  ON  THE  WASTING  DISEASES  OF  CHILDREN. 
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$2  50.  (Just  issued.) 


10  HENRY  C.  LEA'S  PUBLICATIONS. 


SARGENT  (?.  W.)  ON  BANDAGING  AND  OTHER  OPERATIONS 
OF  MINOR  SURGERY.  New  edition,  with  an  additional  chapter 
on  Military  Surgery.  In  one  handsome  royal  12mo.  vol.  of  nearly 
400  pages,  with  184  wood-cuts,  extra  cloth,  $1  75. 

SMITH  (J.  LEWIS.)  A  TREATISE  ON  THE  DISEASES  OF  IN- 
FANCY AND  CHILDHOOD.  Second  edition.  (Now  ready.)  In 
one  large  Svo.  volume  of  over  700  pages,  cloth,  $5  ;  leather,  $6. 

SHARPEY  (WILLIAM)  AND  QUAIN  (IONES  AND  RICHARD). 
HUMAN  ANATOMY.  With  notes  and  additions  by  Jos.  Leidy, 
M.D.,  Prof,  of  Anatomy  in  the  University  of  Pennsylvania.  In  two 
large  Svo.  vols.  of  about  1300  pages,  with  51 1  illustrations,  extra  cl.  $6. 

SKEY  (FREDERIC  C.)  OPERATIVE  SURGERY.  In  one  Svo.  vol. 
of  over  650  pages,  with  about  100  wood-cuts,  cloth,  $3  25. 

SLADE  (D.  D.)  DIPHTHERIA  ;  ITS  NATURE  AND  TREATMENT. 
Second  edition.  In  one  neat  royal  12mo.  vol.,  extra  cloth,  $1  25. 

OMITH  (HENRY  H.)  AND  HORNER  (WILLIAM  E.)     ANATOMICAL 

^     ATLAS.  Illustrative  of  the  structure  of  the  Human  Body.  In  one  large 

imperial  Svo.  vol.,  with  about  650  beautiful  figures,  extra  cloth,  $4  50. 

SMITH  (EDWARD).  CONSUMPTION;  ITS  EARLY  AND  REME- 
DIABLE STAGES.  In  one  Svo.  vol.  of  254  pp.,  extra  cloth,  $2  25. 

STILLE  (ALFRED).  THERAPEUTICS  AND  MATERIA  MEDIC  A. 
Fourth  edition,  revised  and  enlarged.  In  two  large  and  handsome 
volumes  Svo.  (Preparing.) 

S  \LTER  (H.  H.)  ASTHMA  ;  ITS  PATHOLOGY,  CAUSES,  CONSE- 
QUENCES, AND  TREATMENT.  In  one  volume  Svo.,  extra  cloth, 
$250. 

SCHMITZ  AND  ZTTMPT'S  CLASSICAL  SERIES.  In  royal  18mo. 
CORNELII  NEPOTIS  LIBER  DE  EXCELLENTIBUS  DUCIBUS 
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bound,  70  cents. 

C.  C.  SALLUSTII  DE  BELLO  CATILINARIO  ET  JUGURTHINO. 

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70  cents. 
Q.  CURTII  RUFII  DE  GESTIS  ALEXANDRI  MAGNI  LIBRI  VIII. 

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90  cents. 
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85  cents;  half  bound,  $1. 
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ADVANCED    LATIN    EXERCISES,     WITH     SELECTIONS    FOR 

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half  bound,  70  cents. 

qWAYNE   (JOSEPH  GRIFFITHS).     OBSTETRIC  APHORISMS.     A 
O     new  American,  from  the  fifth  revised  English  edition.     With  addi- 
tions by  E.  R.  Hutchins,  M.  D.     In  one  small  12mo.  vol.  of  177  pp., 
with  illustrations.     Extra  cloth.  $1  25.     (Just  issued.) 


HENRY  C.  LEA'S  PUBLICATIONS.  11 


OCHOEDLER  (FREDERICK)  AND  MEDLOCK  (HENRY).   WONDERS 

^     OF  NATURE.   An  elementary  introduction  to  the  Sciences  of  Physics, 

Astronomy,     Chemistrj',    Mineralogy,    Geology,    Botany,     Zoology, 

and  Physiology.     Translated  from  the  German  by  H.  Medlock.     In 

one  neat  8vo.  vol.,  with  679  illustrations,  extra  cloth,  $3. 

SMALL  BOOKS  ON  GREAT  SUBJECTS.  Twelve  works;  each  one  10 
cents,  sewed,  forming  a  neat  and  cheap  series  ;  or  done  up  in  3  vols., 
extra  cloth,  $1  50. 

QTRICKLAND    (AGNES).     LIVES  OF  THE  QUEENS   OF   HENRY 
£     THE  VIII.  AND  OF  HIS  MOTHER.     In  one  crown  octavo  vol., 

extra  cloth,  $1 ;  black  cloth,  90  cents. 
MEMOIRS  OF  ELIZABETH,  SECOND  QUEEN  REGNANT  OF 

ENG  LAND  AND  IRELAND.     In  one  crown  octavo  vol.,  extra  cloth, 

$1  40;  black  cloth,  $1  30. 

rpANNER  (THOMAS  HAWKES).  A  MANUAL  OF  CLINICAL  MEDI- 
-L  CINE  AND  PHYSICAL  DIAGNOSIS.  Third  American  from  the 
second  revised  English  edition.  Edited  by  Tilbury  Fox,  M.  D.  In 
one  handsome  12mo.  vol.  of  366pp.,  cloth,  $1  50.  (Lately published.) 
-  ON  THE  SIGNS  AND  DISEASES  OF  PREGNANCY.  First 
American  from  the  second  English  edition.  With  four  colored  plates 
and  numerous  illustrations  on  wood.  In  one  vol.  8vo.  of  about  500 
pages,  extra  cloth,  $4  25. 

rKE  (DANIEL  HACK)      INFLUENCE  OF  THE  MIND  UPON  THE 
BODY.     In   one  handsome  8vo.  vol.  of  416  pp.,  extra  cloth,  $3  25 
(Now  ready.) 

rp A YLOR    (ALFRED    S.)     MEDICAL    JURISPRUDENCE.     Seventh 
J-      American  edition.     (Preparing.) 

PRINCIPLES  AND  PRACTICE  OF  MEDICAL  JURISPRU- 
DENCE. From  the  Second  English  Edition.  In  one  large  8vo. 
vol.  (Nearly  ready.) 

ON  POISONS  IN  RELATION  TO  MEDICINE  AND  MEDICAL 

JURISPRUDENCE.  Third  American  from  the  Third  London  Edi- 
tion. 1  vol.  8vo.  (Preparing.) 

rpHOMAS  (T.  GAILLARD).    A   PRACTICAL   TREATISE  ON   THE 

J-     DISEASES  OF  FEMALES.     Third  and  enlarged  edition.     In  one 

large  and  handsome  octavo  volume  of  784  pages,   with   about  250 

illustrations.      Extra  cloth,  $5  00 ;     leather,  $6  00.     (Jnst  issued.) 

T3DD  (ROBERT  BENTLEY).  CLINICAL  LECTURES  ON  CERTAIN 
ACUTE  DISEASES.  In  one  vol.  8vo.  of  320  pp.,  extra  cloth,  $2  50. 

THOMPSON  (SIR  HENRY).  CLINICAL  LECTURES  ON  DISEASES 

J-  OF  THE  URINARY  ORGANS.  In  one  8vo.  volume  of  204  pages, 
with  illustrations,  extra  cloth,  $2  25.  (Lately  issued.) 

THE   PATHOLOGY  AND  TREATMENT  OF  STRICTURE  OF 

THE  URETHRA  AND  URINARY  FISTULA.  From  the  third 
English  edition.  In  one  8vo.  vol.  of  359  pp.,  with  illustrations,  extra 
cloth,  $3  50.  (Lately  issued.) 

WALSHE  (W.  H.)  PRACTICAL  TREATISE  ON  THE  DISEASES 
OF  THE  HEART  AND  GREAT  VESSELS.  Third  American  from 
the  third  revised  London  edition.  In  one  8vo.  vol.  of  420  pages 
extra  cloth,  $3. 

WOHLER'S  OUTLINES  OF  ORGANIC  CHEMISTRY.  Translated 
from  the  8th  German  edition,  by  Ira  Remsen,  M.D.  In  one  neat 
12mo.  vol.,  extra  cloth,  $3  00.  (Now  ready.) 


12  HENRY  C.  LEA'S  PUBLICATIONS. 


WALES  (PHILIP  S.)  MECHANICAL  THERAPEUTICS.  In  one 
large  8vo.  vol.  of  about  700  pages,  with  642  illustrations  on  wood, 
extra  cloth,  $5  75 ;  leather,  $6  75. 

WELLS  (J.  SOELBERG).  A  TREATISE  ON  THE  DISEASES  OF 
THE  EYE.  Edited  with  additions  by  I.  Minis  Hays,  M.  D.  In  one 
large  and  handsome  octavo  vol.  of  736  pp.,  with  6  colored  plates  and 
216  wood-cuts,  also  selections  from  the  teat-types  of  Jaeger  and  Snel- 
len,  extra  cloth,  $5;  leather,  $6. 

Tin-HAT  TO   OBSERVE  AT  THE   BEDSIDE  AND  AFTER   DEATH 
VV   IN  MEDICAL  CASES.    In  one  royal  12mo.  vol.,  extra  cloth,  $1. 

WATSON  (THOMAS).  LECTURES  ON  THE  PRINCIPLES  AND 
PRACTICE  OF  PHYSIC.  A  new  American  from  the  fifth  and  en- 
larged English  edition,  with  additions  by  H.  Hartshorne,  M.D.  In 
two  large  and  handsome  octavo  volumes.  (Now  ready.)  Extra 
cloth,  $9  ;  leather,  $11. 

(CHARLES).  LECTURES  ON  THE  DISEASES  PECULIAR 
TO  WOMEN.  Third  American  from  the  Third  English  edition.  In 
one  octavo  volume  of  550  pages,  extra  cloth,  $3  75;  leather,  $4  75. 

LECTURES  ON  THE  DISEASES  OF  INFANCY  AND  CHILD- 

HOOD.  Fourth  American  from  the  fifth  revised  English  edition.  In 
one  large  8vo.  vol.  of  656  closely  printed  pages,  extra  cloth,  $4  50  ; 
leather,  $5  50. 

ON   SOME   DISORDERS    OF    THE   NERVOUS   SYSTEM   IN 

CHILDHOOD.     From  the  London   Edition.     In  one   small  12mo. 
volume,  extra  cloth,  $1.      (Now  ready.) 

AN  ENQUIRY  INTO  THE  PATHOLOGICAL  IMPORTANCE 

OF  ULCERATION  OF  THE  OS  UTERI.     In  one  vol.  8\ro.,  extra 
cloth,  $1  25. 

WILLIAMS  (CHARLES  J.  B.)  PRINCIPLES  OF  MEDICINE.  A 
new  American  from  the  third  revised  London  edition.  In  one  8vo. 
vol.  of  about  500  pages,  extra  cloth,  $3  50. 

PULMONARY  CONSUMPTION  :  ITS  NATURE,  VARIETIES. 

AND  TREATMENT.     In  one  neat  octavo  volume.     Cloth,  $2  50. 
(Now  ready.) 

WILSON  (ERASMUS).  A  SYSTEM  OF  HUMAN  ANATOMY.  A 
new  and  revised  American  from  the  last  English  edition.  Illustrated 
with  397  engravings  on  wood.  In  one  handsome  8vo.  vol.  of  over 
600  pages,  extra  cloth,  $4  ;  leather,  $5. 

ON  DISEASES  OF  THE  SKIN.     The  seventh  American  from 

the  last  English  edition.     In  one  large  8vo.  vol.  of  over  800  pages, 
extra  cloth.  $5. 

Also,  A  SERIES  OF  PLATES,  illustrating  "Wilson  on  Diseases  of  the 
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colored,  representing  about  one  hundred  varieties  of  Disease.  $5  50. 

Also,  the  TEXT  AND  PLATES,  bound  in  one  volume,  extra  cloth,  $10. 

THE  STUDENT'S  BOOK  OF  CUTANEOUS  MEDICINE.     In 

one  handsome  royal  12mo.  vol.,  extra  cloth,  $3  50. 

TfiriNSLOW  (FORBES).    ON  OBSCURE  DISEASES  OF  THE  BRAIN 
VY  AND  DISORDERS  OF  THE    MIND.     In  one  handsome  8vo.  vol. 
of  nearly  600  pages,  extra  cloth,  $4  25. 

WINCKEL  ON  DISEASES  OF  CHILDBED.  Translated  by  Chad- 
wick.  (Preparing  ) 

I7EISSL     ON    VENEREAL     DISEASES.       Translated     by    Sturgis. 
£-1    (Preparii)g.) 


DATE   DUE   SLIP 

UNIVERSITY  OF  CALIFORNIA  MEDICAL  SCHOOL  LIBRARY 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


KIrkes,  ^547 

K59b    Handbook  of  physiology 
1873    £$•.  by  W.M.fcaker.   A. 


new  America]}!  from  the 
8lh  enl.  English  ed. 


-V. 


-rtARY 


